Small grains — wheat, rye, oats, barley, and triticale — are important agricultural crops in Georgia, South Carolina, Alabama and northern Florida. Winter wheat is a significant cash grain crop in the Southeast, and rye, oats and wheat are planted on hundreds of thousands of acres in each state for winter grazing. Currently, winter barley production is limited, and triticale is a potential cash crop but is not grown extensively in the Southeast.

Small grains are adaptable to multiple-cropping systems, and high grain and forage yields under dry land conditions are attractive features. Wheat is the most important winter grain crop in the southern United States and is typically grown in a doublecrop system with soybean or cotton. Wheat grain acreage in the four southeastern states has been as high as 2+ million acres but currently is about 0.5 to 0.7 million acres, with an estimated gross value of $120 million per year. Furthermore, Georgia is the No. 1 producer of rye in the country.

State average wheat yields have gradually increased over the past 15 years from about 30 to 35 bushels per acre (bu/A) to 45 to 50 bushels per acre. However, a disparity exists between state average yields and yields achieved by top producers, who often reach 80 to 100+ bu/A. The potential for greatly increasing production of small grains exists, but better use of management technologies in needed to realize this potential.

The objective of this handbook is to provide rapid and extensive transfer of modern management technologies for small grain production. The intended audience includes Extension agents, industry personnel and dedicated producers. It is multidisciplinary in scope and includes extension and research scientists from agronomy, agricultural economics, agricultural engineering, animal science, entomology and plant pathology from four southeastern states: Georgia, Alabama, South Carolina and Florida.

This is a revision of the Small Grain Handbook originally published by the University of Georgia College of Agriculture in 1989. This handbook revision was developed by the Southeastern Small Grains Team and is jointly published by the University of Georgia and Auburn University Agricultural Experiment Stations and Cooperative Extension Services.

From the Editors:

G. David Buntin
Barry M. Cunfer

Proper management of wheat for optimum yields requires that certain practices such as nitrogen fertilization and application of pesticides be timed at specific stages of wheat growth. To benefit from these management practices, the grower should understand the growth and development of the plant.

Growing Degree Days

The pattern of development of the wheat plant can be used to guide crop management. Plant development is timed by growing degree days (GDD). Wheat grows and develops when the average daily temperature exceeds 32ºF. Wheat development in relation to temperature can be determined by the number of wheat GDD. Wheat GDD are based on Celsius temperatures and are calculated by the formula: average daily (ºF) = (max. + min.)/2; then convert degrees F to degrees Celsius (ºC) = (5/9) (ºF-32). Average daily temperatures less than 32ºF are recorded as 32 because this is the lowest threshold for growth and development. Examples of GDD at several average daily temperatures (ADT) are: ADT of 32 = 0 GDD, ADT of 50 = 10 GDD, ADT of 60 = 16 GDD and ADT of 70 = 21 GDD. A GDD calculator can be found on the Web at www.griffin.uga.edu/bae/.

Germination

Figure 1. Anatomical description of wheat at the vegetative stage

Figure 2. Comparison of leaf characteristics between wheat and other small grains

Wheat germinates at temperatures between 39º and 90ºF with optimal germination occurring at 68º to 77ºF. Germination is indicated by radicle (primary root) protrusion through the seed coat, followed by emergence of the coleoptile (first leaf) which surrounds and protects the emerging stem and primary leaves. Germination normally is complete within four to six days at optimum temperatures. The number of wheat GDD it takes to germinate is 80 and to emerge is 50, for a total of 130 GDD in the Southeast.

Wheat produces a root and crown (nodal) system that develops sequentially according to a pattern typical of grasses. The wheat plant has two types of roots: the seminal and the crown (nodal). Seminal roots form from groups of cells already present in the seed (Figure 1). This system usually comprises three to six main roots and their branches. The first seminal root to appear is called the radicle. It is the first root produced when a seed germinates. The rest of the seminal roots arise from the nodes. Variety and seed size are the main factors that affect the number of seminal roots in the germ.

Crown roots are produced on main stems, primary tillers and secondary tillers (Figure 1). Each main-stem node develops two roots after the leaf first appears. If a tiller is produced at the node, one and sometimes two roots elongate after the first appearance of a leaf at the node. Generally, each leaf takes about 100 GDD to develop.

Crown roots generally begin to grow from tillers after a tiller has at least two leaves. The root axes on tillers elongate in an orderly and predictable way with respect to time. After a tiller has three emerged leaves, the length of roots increases. The depth of rooting increases directly with root number and is also influenced by the soil profile. By the time wheat reaches jointing or early boot stage, new root production ceases, and growth continues in the existing roots. Each tiller has its own roots, which begin to appear when the tiller has two to three leaves.

Seedling Growth

Seedling growth occurs from coleoptile (first leaf) emergence to tiller development. Generally, the wheat plant develops three or more leaves prior to tillering. The rate of individual leaf growth as well as the final shape and size of the leaf are affected by the environment. During vegetative growth, wheat can be distinguished from other small grain crops by its short hairy auricles, which are located at the point where the leaf blade and sheath meet (Figure 2).

Tillering

Tillering is the development of shoots from buds at the base of the main stem (Figure 1). The count of leaves on the main stem is a good way to measure plant development and is linearly related to GDD. Planting to six leaves on the main stem (three tillers) requires about 730 GDD. During initial development, the tiller is dependent upon the main shoot for nutrition, but once the tiller develops approximately three or more leaves, it becomes independent of the parent plant for nutrition and will form its own roots. Varieties show relatively little variation (5 percent to 10 percent) in leaf development rate. Planting date or season-to-season climate variation, appear to create greater change in leaf development rate than variety.

Secondary tillers may also arise from primary tillers. The extent of tillering is dependent upon genetic and environmental factors. Tillering increases with high light intensity, reduced plant populations, and high soil nutrient (primarily nitrogen) availability. High temperatures, high plant populations, soil moisture stress and pests can reduce tillering. Although each tiller has the potential to bear a productive seedhead, generally, about one-half of the tillers do not survive to bear grain. Aborted tillers are affected early in tiller development, long before visual evidence of tiller death is evident.

If a plant that has been stressed during vegetative development is exposed to a favorable environment, rapid tiller growth can improve grain yield. Often low plant populations compensate by increasing numbers of tillers per plant.

Vernalization

The onset of reproduction is controlled by vernalization. Vernalization is the induction of the flowering process by extended exposure of the shoot apex to low temperatures. Vernalization has been shown to occur in seeds as soon as they absorb water and swell. The effectiveness of vernalization declines with increasing plant age. Vernalization is affected by photoperiod, in that exposure of the plant to short days replaces the requirement for low temperatures in some varieties. Also, if wheat is exposed to high temperatures (86ºF or 30ºC) shortly after low temperatures, vernalization will not occur. After vernalization, the initiation of flowering may be hastened by longer photoperiods, because wheat is a long-day plant requiring night periods to be shorter. Generally, early maturing varieties require fewer chilling hours of vernalization than late maturing ones.

The ability of plants to survive low temperatures depends on whether the plants have been exposed to low temperatures — a hardening process. Later maturing varieties usually survive lower temperatures better than earlier maturing ones. Wheat will go into winter dormancy and grow very slowly when the temperature decreases to 40ºF or below. The vernalization requirements for varieties grown in the Southeast range from one day to six weeks.

Jointing

Jointing or stem elongation begins when the first internode of the stem is visible. Generally, wheat stems possesses six internodes, with internodes increasing in length from the base of the plant to the top. Stem height is under genetic control, but the environment affects genetic expression. The end of the jointing stage is indicated by the appearance of the "flag" leaf, which is the last leaf to develop before grain head emergence. From planting to jointing requires about 1,350 GDD.

Boot Stage

Reproductive development is first observed when the head begins to swell within the flag leaf sheath (boot stage). The head is composed of rows of spikelets on the terminal end of the last stem internode (rachis). Each spikelet produces two to five florets, and each floret may produce a single grain. The number of spikelets formed depends upon environmental conditions during early jointing. High temperatures increase the rate of spike development but reduce the number of spikelets per head. Moisture stress reduces spikelet number. High light intensities and optimal nitrogen fertilization increase spikelet numbers. The boot stage ends when the grain head first emerges from the flag leaf sheaf.

Heading Stage

The heading stage is first observed when the head emerges from the flag leaf sheath. Small grains are normally self-pollinated. Pollination begins in the middle region of the head and progresses to the tip and base. High temperatures and drought stress during heading can reduce pollen viability and reduce grain number.

Freezing temperatures may result in head injury and partial or complete sterility during jointing and heading. Few differences among varieties have been found for cold damage during this growth stage. However, short-season (early maturing) wheat varieties are usually more susceptible to injury by freezing temperature because they produce heads earlier in the year than full-season varieties.

Grain Filling

The grain filling stage follows the heading stage. Environmental factors, primarily high temperature and moisture stress, affect kernel survival and the rate and duration of grain development. Starch and protein are the primary storage reserves in the mature kernel. Starch deposition within the grain is under greater environmental influence than protein accumulation. Under high temperature and moisture stress conditions, starch concentration and final grain dry weight are reduced.

Grain Ripening

Small grains are physiologically mature in the hard dough stage. The moisture content may range from 25 percent to 35 percent. The entire plant then loses chlorophyll and assumes a characteristic straw color. At this point, the crop is ready for harvest (13 percent to 16 percent moisture).

Yield is a function of genetics and environment. The yield of a given variety is dependent upon the following yield components:

The factor most directly associated with yield is kernel number per unit area, yet, this factor is dependent upon tiller production, head development, and seed development.

Development Scales

Several small grain development scales have been developed. The two scales most frequently used are the Feekes’ and Zadoks’ scales (Table 1, Figure 3). The Feekes’ scale provides a numerical system for describing wheat growth, but is not very specific during the germination, seedling, jointing, and booting stages. The Zadoks’ scale is based on a two digit descriptive system, which allows for more detail in quantifying wheat development. These growth scales allow for comparisons of development among varieties in varying environments and they aid the proper timing of management practices such as nitrogen fertilization and pesticide treatments.

Figure 3. Diagrammatic comparison of Zadoks’ and Feekes’ scales of wheat development

Table 1. Description and comparison of Zadoks' and Feekes' wheat development scales

Well-adapted, high-yielding wheat varieties with resistances to the prevalent diseases and insects are essential for profitable wheat production. Varieties adapted to one area are not necessarily suitable for other areas. Even recommended varieties within a production region vary in yield potential, disease and insect resistance, straw strength, and maturity. Therefore, it is important to carefully evaluate available varieties and plant those that best fit field needs. Errors made in variety selection may result in loss of yield or additional input costs.

Factors to Consider

Yield

Grain yield is normally the primary consideration. Consistent high yields over several years are usually a good indication of well-adapted varieties. However, growers should also consider other factors listed below.

Maturity

Early-maturing varieties ripen about one to two weeks before medium maturing varieties. Early-maturing varieties are most suitable for doublecropping systems. If you are planting a large acreage, use several adapted varieties of differing maturities to increase planting and harvesting efficiency. Late varieties should be planted first, followed by medium, and finally, the early-maturing varieties. If you have to plant later than the recommended date, note that early-maturing varieties usually perform best.

Disease Resistance

Leaf rust, Stagonospora nodorum blotch, and powdery mildew are important wheat diseases. Resistance to these diseases should be considered when selecting varieties. Resistance to leaf rust is most important in the lower Coastal Plain and resistance to powdery mildew is most important under high nitrogen fertility or maximum yield conditions.

Insect Resistance

Hessian fly is the major insect pest of wheat in the Southeast. The most effective and economic means of controlling the Hessian fly is by using resistant varieties. Because Hessian fly populations vary greatly from region to region, varieties reported as resistant in one area of the USA may be susceptible here. See the section on insect management and control for more information.

Straw Strength

Select varieties with good straw strength to prevent harvest losses associated with lodging. Semi-dwarf varieties are short in height and usually have good straw strength, even when high rates of nitrogen fertilizer are used.

Test Weight

Standard test weight for U.S. No. 2 soft red winter wheat is 58 pounds per bushel (lb/bu). Test weights below this standard can result in a price dockage at the elevator. Light wheat with a test weight of 48 to 52 pounds per bushel has low feeding value and lower energy content due to increased fiber content. Environmental conditions, disease and insect damage, and variety strongly influence test weight.

Selecting Varieties for Forage Production

Make sure that varieties selected for forage production have a record of high forage yield. Varieties that produce high grain yield do not always produce high forage yield. Varieties that steadily produce forage throughout the season may be more desirable than varieties with only seasonal growth. If you plan to use wheat for forage and also produce a grain crop, select varieties with high yield potential for both forage and grain production. Use a Hessian fly resistant variety to reduce damage associated with early planting required for fall and early winter forage production.

State Wheat Performance Tests

Each year variety performance tests are conducted to determine the adaptability of available and prospective wheat varieties. Both forage and grain tests are conducted at locations that represent all the major production regions. These results are presented annually in agricultural experiment stations publications and are available at your local Cooperative Extension office by late August each year. These performance data help you judge the merits of wheat varieties.

How to Use the Small Grains Performance Tests Report

1. Select the test location that best represents your production area.
2. Use multiple year averages, because they are the best predictors of performance.
3. Select current varieties you are familiar with and use them to compare other entries.
4. Identify those varieties that out-yielded your current varieties.
5. If the yield difference between varieties is greater than the LSD value, the varieties are considered statistically different in yield. Yield differences smaller than the LSD value may be due to random variability rather than actual variety differences.
6. Check the other columns for test weight, lodging, height, winter survival and heading date. Avoid varieties with low test weight, high lodging or low winter survival. Be cautious about any wheat variety that heads substantially earlier or later, or is significantly taller or shorter than your current variety.
7. Refer to supporting tables presenting variety characteristics for general ratings of agronomic characters, disease resistance, and insect resistance.
8. Once you have identified one or more varieties that you would like to try, refer to the table titled "Sources of Seed" and contact the variety source for information on availability of seed.

Your soils and management may differ from those of the test location. Therefore you may first wish to plant strips or a small acreage of the better-performing varieties before planting large acreages of them.

Recommended Varieties

Recommended varieties are determined by a critical evaluation of variety performance by research and extension scientists. Recommendations are based on the relative performance of a variety for three or more years, taking into account the importance of diseases, insects, and weather conditions in each of the production regions.

For a list of recommended varieties in your production region, consult the Cooperative Extension fall planting schedule, available at your local Extension office.

Selecting high-yielding varieties and high-quality seed is one of the most important planning decisions in the planting of small grains. Most economic analyses list seed costs as less than 10 percent of total production costs. On the other hand, seed quality and variety selection determine yield potential and many times are the difference between profit and loss.

Seed quality is a collective term to describe the expected performance of a seed, bag of seed or seed lot. It includes standardized measurements of germination percentage, genetic purity, other crop seed, weed seed and inert material. The term seed quality may also include non-standardized measurements of physiological health, vigor and the presence of pathogenic organisms. The standardized measurements are routinely determined by state or private seed laboratories and are required to be listed on each seed tag. The non-standardized measurements are normally used for quality control to select superior lots of seed for sale. However, the non-standard measurements are also available to individuals by special request and need.

Commercial Seed Classes

Farmers can be best assured of high seed quality by purchasing their planting seed from reputable seedsmen. Seed purchased and/or planted by farmers can be placed into one of three classes: certified, non-certified and farmer-saved seed.

• Certified seed, produced by professional seedsmen who are members of crop improvement associations, is distributed by commercial seed dealers. Seed certification is a third party, limited generation, quality control program covering seed fields, conditioning plants, and other critical areas. A major role of the certification program is to deliver new varieties with superior disease resistance, yield, or quality characteristics to commercial growers. The certification staff monitors the seed multiplication process and verifies that the production has met the criteria necessary to protect the genetic identity of new varieties. In addition certification ensures that the genetic purity of older, but highly productive varieties remains stable and the variety remains true to type. While varietal purity is the first consideration in seed certification, other quality standards are important including germination, weed seed, other crop seed, and inert matter content. Certified seed must meet significantly higher standards than is required by state seed laws.
• Non-certified seed also is distributed by commercial seed dealers, but usually do not have third party verification of quality. Seed companies with large breeding programs do not always participate in certification, but many times establish company seed standards which are usually higher than the minimum standards of the state seed law. Non-certified seed may or may not be grown by professional seed producers, but seed quality is known and labeled according to state laws.
• Farmer-saved seed is saved by a farmer to plant on their farm or to sell to a neighbor. They are not required to meet any provisions of the state seed law, provided the seed are sold at the farm, not advertised, or transferred by public carrier. Labeling of farmer to farmer seed is not required. Therefore, little if any recourse is available if the seed fails to produce a stand. Numerous seed surveys conducted by extension and research personnel across the United States report farmer-saved seed consistently produced lower yields. Weed seed contamination, low germination, and unknown or mixed varieties generally lead to the lower yields and lower profits.

State Seed Laws

State departments of agriculture regulate labeling of commercial seed. Seed laws are designed to prevent the misrepresentation of seed and set minimum standards for important seed quality criteria (Table 2). They require all seed offered for sale to be labeled with an analysis tag. Any accredited seed laboratory can determine the seed quality data for the analysis tag. However, the data collected by state departments of agriculture from official samples determine final suitability for sale in the individual states. In addition to the state departments of agriculture, the Federal Seed Branch also regulates seed sales, but it is concerned only with seed traded across state lines.

Table 2. Comparison of analysis requirements as percentage of net weight for classes of seed (Example: wheat, state of Georgia)

A typical seed tag provides the following information:

• Kind and variety – The kind of a crop refers to the species (wheat, oats, barley, rye, etc.) The variety is a subdivision of a kind characterized by growth, yield, fruit or other characteristics that differentiate it from other plants of the same kind. Maturity date, cold tolerance, and disease and pest resistance are variety specific. Contamination of one variety by another may compromise the desirable characteristics of superior varieties. Therefore, genetic purity of planting seed is an extremely important quality factor. Knowledgeable and expert farmers select genetically superior varieties and buy professionally grown seed to ensure varietal purity and trueness to type.
• Germination percentage – Germination is the ability of a seed to produce a normal seedling under favorable conditions. The laboratory analysis report of percent germination is based on pure seed and not on the total contents of a bag. Actual seed germination potential is greatly influenced by weather conditions during the growing and harvesting seasons. Drought during the growing season may result in immature seed, whereas excessive rainfall may increase disease levels. The storage environment, moisture, temperature and presence of insects also will determine final seed quality. Mechanical damage will cause low seed quality and is caused by improperly adjusted combines, poorly maintained augers, excessive drying temperatures, and high speed impact on hard surfaces in elevators, bins, and trucks.
• Pure seed – Pure seed percentage gives the percentage of total weight of each kind and variety tested. If more than one kind and/or variety is named, the pure seed percentage of each component must be listed. High quality small grain seeds should always be at least 98 percent pure seed and of one kind and variety.
• Inert matter – Inert matter includes sand, stones, dirt, sticks and plant parts including pods, chaff and broken seeds. A broken seed is considered inert if it is 50 percent or less of a whole seed. Broken seeds greater than 50 percent of a whole seed are included in pure seed percentage and are considered whole seed for germination purposes. High quality, professionally grown and conditioned small grain seed should have below 2 percent inert matter.
• Other crop – Other crop may be a contaminant of another kind of small grain or a different variety. In some instances the other crop may be a weed in small grains, but an economically important crop in another planting environment (i.e., ryegrass, cheat, clover or canola). These other crop seed may suggest poor quality controls in seed production and conditioning. Crop plants other than the intended kind may reduce yield and grade and should be avoided.
• Weed seed – The presence of weed seed is expressed in percentage of total bag weight. It includes seeds, but also bulblets of wild garlic and plant parts of wild radish. High quality seed should contain no weed seed.
• Noxious weed seed – Noxious weeds are plants that are extremely difficult to control and prolific seed producers. Weeds are declared noxious by state departments of agriculture in a cooperative effort to limit their spread and economic damage. See Table 3 for a listing of the noxious weeds as declared by regulations of the Georgia Department of Agriculture. Other states have similar lists. High quality seed should not contain noxious weed seed.

Table 3. Comparison of noxious weed seeds allowed in various classes of seed

Other data required on the seed tag gives information about the specific lot of seed and individual containers. Required labeling information is listed below and in the example in Figure 4a.

• Lot number is a designation placed on each container to serve as a reference of lab reports, producer, year of production, etc. The lot number may be a simple numeric designation as "3" or quite complex as R-6036-JC. The latter number can code for several variables useful in quality control and inventory management.
• Net weight is the quantity of seed in the container exclusive of container weight.
• Origin is the state where the seed was grown. Origin may be an important consideration for crop adaptability when purchasing seed.
• Hard seed does not germinate with standard germination tests, but will germinate upon special treatment such as scarification after ripening, etc. Small grains normally do not have hard seed.
• Dormant seed are viable seeds, other than hard seed, which fail to germinate when provided favorable conditions. Dormant seed may normally germinate over time with exposure to proper conditions.
• Test date is the date that the seed laboratory reported the germination test. State seed regulations require that the test date be within nine months of the date of sale, not including the month of the test. Federal regulations require that the test date be within five months of the date of interstate sale, not including the month of test.
• Name and address of vendor refers to the company responsible for the seed in the bag. In most cases, the vendor is the business that conditioned and bagged the seed for sale or the owner of the seed if another party accomplished conditioning.

Figure 4a	Figure 4b

Certified Seed

Every state seed producer has access to a certification agency to assist in the production of high quality seed. These certification agencies administer the production and quality standards established by the membership. The certification label gives the highest level of assurance that the seed in the bag meets the highest quality standards in the seed industry. The certification office also maintains records for each certified seed lot, which includes the following: source of seed planted, application for field inspection and certification, field inspection, bin, conditioning, laboratory report and a sample label from each lot of seed.

The state crop improvement associations were first organized to educate seed growers and consumers about the advantages of high quality seed and provide assurance of seed quality in the bag. During recent seasons and years, with the advent of the Plant Variety Protection Law (PVPA) and expansion of private breeding programs, many private breeding companies have relied on certification for third-party, unbiased quality control. Certified seed is recognized as the best assurance for quality control from the field to the bag. Certification identifies member seedsmen as supporters and providers of high quality planting seed.

Membership in the state crop improvement association is available to qualified seed producers who desire to make certified seed growing a part of their operation. The local county Extension agent can provide appropriate information, addresses and telephone numbers.

There are four classes of certified seed: breeder, foundation, registered and certified. These classes are designed as a four-generation seed increase program to reduce genetic drift and the risk of mechanical contamination. The specific standards for each crop are more restrictive in the foundation class than the registered class and less restrictive in the certified class. In all cases, the standards for foundation and registered seed are established to ensure that the certified class has a high level of genetic purity. Each class of certified seed is described in detail as follows:

• Breeder seed are produced under the direct supervision of the originating plant breeder or institution.
• Foundation seed are grown from breeder seed. Foundation seed are tagged with a white label. The production of foundation seed is highly specialized and usually managed by an organization that has foundation seed production as its primary responsibility. Private companies usually have a specific department for foundation seed production. Foundation seed lots do not normally enter the commercial seed channels but are used by professional seed producers to produce registered and certified seed.
• Registered seed are grown from foundation seed. Registered seed are tagged with a purple label. Recently private and public breeding programs are eliminating the Registered class to provide greater assurance of varietal purity and to limit the unauthorized production and sale of PVP protected varieties.
• Certified seed are grown from foundation or registered seed. Certified seed also are inspected and must meet state seed certification minimum standards. These seed with known pedigree and performance are distributed by commercial seedsmen. Certified seed are tagged with a blue label (Figure 4b). The familiar blue tag found on each bag of certified seed assures the farmer that the seed have passed an unbiased field and laboratory inspection process.

Selecting Good Seed

Yields and profits are greatly dependent on the proper selection of planting seed. Many quality factors must be considered before purchasing seed. An acceptable level for each quality factor must be established.

Perhaps the first and most important decision to make is selection of an adapted variety. The choice of variety sets the upper limit on yield and quality. Trueness to type and varietal purity is just as important as selecting a high yielding variety name. By purchasing professionally grown seed, especially certified seed, the farmer has more assurance of receiving the correct variety with high varietal purity.

Be a seed tag reader. The seed tag reveals the quality of the seed so that the farmer can make a rational decision. It is best to purchase seed with germination above 80 percent, pure seed content above 98 percent, low inert matter and preferably no weed seed. Other crop seed should be less than 0.10 percent.

Remember, cheap seed is usually cheaper for a reason. Seed offered for sale without a seed tag may have a quality problem that could result in poor stands, noxious weeds or a lower yielding variety than the one selected. Saving a few dollars per acre at planting may result in lower or no profit at harvest.

Small grain seed should be treated for diseases and insects. If appropriate chemicals are used, seed treatment will control loose smut and will give partial to complete control of other seed-transmitted small grain diseases. In addition, seed treatments also are important in reducing seedling disease caused by soil fungi. State law requires that all seed commercially treated be tagged with a warning label stating the chemical used and application rate.

Other Considerations

All seed producers and especially farmers who save their own seed or sell seed to other farmers should be aware of the Plant Variety Protection Act (PVPA). The PVPA allows the owner of a variety to determine who may market or sell a variety for planting purposes.

For varieties protected under the 1970 PVPA (normally those varieties developed between 1970 and 1995), a farmer may save the seed from a crop of a protected variety for his own use or sell to another farmer, if he does not normally grow seed for sale and the amount of seed saved is no more than the amount needed to plant his normal acreage.

The 1994 PVPA amended the original PVPA and applies to varieties protected after 1995. This act prohibits the sale of seed for planting purposes unless specifically given permission by the variety owner. To determine which act applies, read the analysis tag on the seed planted or contact the seed certification agency or state department of agriculture in your state.

Determining Stand Problems

Each year, county agents, seed dealers and certification agencies receive complaints from farmers who fail to get adequate stands. But, often times, a thin stand under proper management will produce high yields. As a result each individual situation should be evaluated on its own merits to determine if replanting is desirable and also to establish a reasonable cause for poor seedling establishment.

There are several potential causes of poor stands. Usually, the first assumption is low quality seed. In actual practice though, poor seed accounts for only a small percentage of deficient stands. Most stand problems are related to improper planting depth, soil moisture and/or seed-soil contact. In other cases, chemical injury and improper fertilizer placement have resulted in poor stands from otherwise high quality seed. Seedborne and soilborne diseases, as well as soil insects, can cause reduction in stands. Diagnosing and understanding the reason for stand failure is the first step toward correcting the deficiency, whether it is a seed problem or it is a result of the planting process.

If the probable diagnosis of a poor stand is seed related, it is usually best to immediately contact the seed dealer. In addition, you may wish to notify the county agent, certification agency and state department of agriculture arbitration officials if it is a serious problem that may be difficult to resolve. The process of gathering data should begin at the first indication of a poor stand and should include seed source records, photographs and verified stand counts.

The discussion of poor stands usually leads to questions about seed vigor. Seed vigor is defined by the Association of Official Seed Analysts as "those properties which determine the potential for rapid, uniform emergence and development of normal seedlings under a wide range of field conditions." Several vigor tests are available to assess seed quality, but none are sufficiently standardized for seed control or labeling purposes. Therefore, seed control officials and the American Seed Trade Association do not encourage labeling or advertising with respect to vigor. However, seed vigor information when properly interpreted may prove valuable when making management or seed storage decisions.

Doublecropping winter wheat with soybeans has become a popular and profitable practice in the Southeast. The long frost-free growing season of the region allows farmers to successfully doublecrop, but higher costs, time and labor constraints, and a desire for less soil erosion have all contributed to increased interest in conservation tillage systems for both crops. New equipment technology for dealing with crop residues, both for drills and deep tillage tools, better herbicides, and the availability of herbicide-resistant soybeans have all enhanced the chances for success.

Soil Compaction

Soil particles (various proportions of sand, silt, and clay, depending on the soil type) are grouped together into aggregates. Aggregates that occur normally are called peds. The larger the aggregates, the more pore space there is for oxygen and water, two important requirements for optimum root growth. When physical forces are exerted on the soil, such as tire traffic and/or tillage, aggregates are broken, or are pressed closer together, reducing the amount of pore space. Less pore space means reduced soil water movement, aeration, and nutrient exchange. The result is a denser, more compact soil, making root growth, rainfall infiltration, and drainage more difficult.

Bulk density is an indicator of how dense or compact the soil is, and is measured as grams of dry soil per cubic centimeter of soil volume. The higher the bulk density, the more compact the soil. For soils with traffic from equipment or livestock, or for soils that have been excessively tilled, the bulk density of the various compacted zones may be so high that crops have difficulty achieving good root growth, and are thus more subject to the detrimental effects of pests or weather extremes such as drought.

Controlled traffic systems reduce the effects of wheel traffic on soil compaction. Tramlines are used so that pesticide and fertilizer application equipment is confined to specific lanes across the field. Electronic tramline systems can be installed on drills so that certain seed drops are blocked so some rows do not get seed to create the tramline areas.

Deep Tillage

Soil compaction can reduce crop yields by restricting root growth. If roots are shallow and do not grow into the subsoil or clay of most soils, they cannot access available soil moisture and nutrients. For most soils, especially those in the Piedmont, there will be a shallow compacted zone about 4 to 6 inches deep that is the result of tillage, primarily with the disk harrow. Because the compacted zone is shallow, chisel plowing to a depth of 8 or 9 inches is usually adequate to break it and allow good crop growth under normal rainfall conditions.

Most doublecropping in the Southeast occurs on the sandy soils of the Coastal Plain. These soils are inherently low in fertility and water holding capacity. They are also susceptible to leaching and often experience significant runoff during the growing season when most rainfall occurs as thunderstorms. The organic matter content of these soils is low, usually less than 1 percent. With excessive tillage, the organic matter content is very difficult to improve and may be as low as 0.5 percent in the lighter textured soils. The low organic fraction contributes to poor soil tilth, which can cause lower rainfall infiltration rates as well as soil crusting. The result is reduced crop productivity, especially under conditions of weather stress, of high or low rainfall.

Most upland sandy soils of the Coastal Plain have a compacted zone or hardpan about 6 to 12 inches below the surface and 2 to 3 inches thick. This is called the E horizon and must be broken so that roots can grow into the subsoil or B horizon for top crop performance. The clay has not only additional moisture but also available nutrients such as nitrogen, potassium, sulfur, manganese and boron.

Deep tillage implements like the chisel plow increase wheat yields in soils typical of the southeastern Coastal Plain. However, in the sandy soils with a highly compacted E horizon, the chiselplow’s spring-loaded shanks will ride on top of the hardpan without rupturing it. Consequently, the effective depth of chisel plowing is often only 7 to 10 inches, rather that the 13 or 14 inches usually needed.

Subsoilers with shanks 20 inches apart or less can be pulled deeply enough to break through most hardpans, but as with chisel plows the deep tillage is done in a furrow-like fashion. With the combined effects of later trips plus the natural effects of reconsolidation, especially during heavy rainfalls, there is potential for compaction to reoccur. Also, subsoilers and chiselplows often leave ridges or a rough surface, which make seeding depth control for wheat difficult.

New Tools for Deep Tillage

Farmers are interested in reducing tillage trips, leaving crop residues for wildlife and to control erosion, while doing a better job of soil hardpan breakage. A number of new conservation tillage/deep tillage implements leave a large percentage of surface residues while essentially breaking compaction zones in almost a broadcast manner. Examples are the Tye Co. and Bigham Bros. Paratill, Worksaver’s Terra-Max, and the French Durou plow. The Paratill uses a slanted shank with subsoiler type points and an adjustable shatter plate behind each shank. The shanks slice through the soil at a 45-degree angle, gently lifting the soil and allowing it to fracture along natural cleavage planes. This action loosens the soil along the bottom of the curved shank without disturbing surface residue. The Terra-Max II plow has one shank per row curved in one direction followed in the same row by another shank curved in the opposite direction. The Durou plow has slanted shanks (20 degrees from the vertical) with a 10-inch-long wing attached to the side of the shank. As with the Paratill, these implements lift the soil and drop it with very little surface disturbance. For these plows, however, there is usually a need for a spike-toothed roller mounted to run just behind the shanks. This is because these implements cause some ridges to form behind the shanks, and smoothing or leveling is needed to help assure uniform depth control.

Wings can be attached to conventional subsoiler shanks to enhance hardpan breakage. The DMI and Yetter companies have optional winged subsoilers commercially available.

Farmers who are considering attaching wings to subsoilers should consider the energy requirements for operating these tools. The wider the wing and closer the shank spacing, the higher the energy necessary for proper operation (Table 4).

Table 4. Tractor size (PTO hp) required to pull one row of various conservation deep tillage implements at 4.5 mph (ground speed) and 15 inches deep in three soil types typical of the southeastern Coastal Plain

* Wings mounted on both sides of subsoiler shanks
Source: A. Khalilian, Clemson University.

Draft and Energy Requirements

Draft and energy requirements of tillage tools are important considerations in selecting tillage systems. The draft needs depend on the soil type and condition, tool shape, travel speed, and depth of operation. Tests were conducted at Clemson’s Edisto Research and Education Center at Blackville, S.C., to determine the energy requirements of the latest technology in deep tillage tools for three typical Coastal Plain soils.

Soil compaction measurements before tillage indicated that each test site had a hardpan or E horizon at about the 10- to 13-inch depth. Soil resistance to penetration in the Varina loamy sand site was higher than that for the Dunbar and Clarendon loamy sand sites. This resulted in higher horsepower requirements for the Varina loamy sand.

One-pass Wheat Planting System

Conventional tillage wheat planting systems in the Coastal Plain typically involve a minimum of two or three diskings to bury the previous crop residue, followed by subsoiling or chiseling for breaking the hardpan, and smoothing with a log or other heavy object dragged behind the deep tillage tool). Deep tillage and smoothing the seedbed should be done as one operation. Disking after deep tillage recompacts the soil and essentially negates most of the positive effects of the deep tillage trip.

To complete the conventional doublecrop system, the wheat residue is either burned or disked, then there is usually a one-pass subsoil/planting operation for soybeans. Energy consumption is high for this system, especially when considering the tillage operations, plus cultivation trips for soybeans. There are considerable cost inputs for labor, equipment, plus the investment in management time required. In addition, there is little attention given to the potential for erosion and runoff with these conventional systems.

A reduced tillage one-pass wheat/soybean system has potential to save energy, reduce erosion and runoff, lower production costs, provide food and cover for quail and other wildlife, and expand the planting interval.

Percent crop residue ground cover after planting soybeans averaged 35 percent for the two one-pass systems, 79 percent for the no-till system and only 13 percent for the conventional tillage doublecropping system. The minimum for meeting conservation tillage requirements is 30 percent ground cover. The one-pass systems for wheat provide the deep tillage critical for optimum production of wheat and soybeans in the Coastal Plain soils and they conserve surface residues.

Fall deep tillage improves wheat yield. No-till wheat yields with deep tillage (either in the fall or spring) are not lower than with conventional surface tillage. Yield increased 18 bu/A in drilled no-till soybeans when the soil was paratilled, both in the fall and spring.

Table 5. One-pass wheat/soybean test results, Edisto REC, Blackville, SC

* One-pass planting
Source: A. Khalilian, Clemson University

Table 6. Wheat and soybean yields for reduced tillage tests at the Pee Dee REC, Florence, SC

Source: J. Frederick et. al., Clemson University

Conclusions

The new winged plows that break soil hardpans in a broadcast fashion, e.g., Paratill and Terra-Max, will be used especially in the Coastal Plain, when considering conservation tillage and the desired residual effects of deep tillage under controlled traffic systems. Deep tillage implements such as the subsoiler and chisel plow will continue to be used, but as farmers switch to reduced tillage to reduce erosion and costs for equipment, labor and energy, there will be shifts toward the newer drill and deep tillage technology. The new herbicide resistance technology for soybeans (e.g., Roundup Ready) will help enhance the chances for success with reduced tillage and drilled systems for soybeans. Controlled traffic systems using tramlines also will reduce soil compaction.

Fertilization and liming are critical management practices for wheat production. A properly managed fertility program, including recommended fertilization and liming practices, can improve yield and quality more than any other single management practice. Such a program includes soil testing, knowledge of crop nutrient requirements and removal, timely application of nutrients, and record-keeping.

Soil pH and Liming

Maintaining proper soil pH is critical to ensure availability and uptake of fertilizer and soil nutrients essential for good wheat production. Economic wheat yields are optimized at soil pH between 6.0 and 6.5. Not only are the essential plant nutrients, including micronutrients, available in this range, but soil elements toxic to plants such as aluminum are kept unavailable.

Liming is the best management practice required to maintain soil pH in the proper range. Lime recommendations should be based on soil testing. It is not uncommon on sandy soils and with modern crop rotations, to need lime applications as often as every year. Dolomitic limestone, which is commonly used, will also provide both essential secondary nutrients, calcium and magnesium.

Nitrogen (N)

Nitrogen rates and timing of application are key management factors for making good wheat yields. Nitrogen is also the most expensive fertilizer nutrient and variable input cost for wheat. Therefore, nitrogen rates should be based on soil potential, cultivar, realistic yield goal, previous crop and residual N. For expected wheat yields of 40 to 70 bu/A, use a total N rate of 80 to 100 lb/A. Adjust this rate based on the preceding crop. If following peanuts or soybeans, decrease the N rate by 20 to 40 lb/A. If following grain sorghum or cotton, increase by 20 to 40 lb N/A. Timing of N fertilization should be based on the pattern of uptake by the crop. Demand for N is relatively low in the fall but increases rapidly in the spring just prior to stem elongation. Therefore, apply 20 to 40 lb N/A at planting, and the remaining N prior to stem elongation. Use the lower rate at planting on heavier-textured soils and the higher rate on sandy soils. Also, excessive N rates applied in the fall could result in a number of problems including surplus vegetative growth, winter kill, disease incidence and possibly nitrate contamination of the groundwater.

When the yield goal exceeds 70 bu/A, use a total N rate of 120 lb/A. Adjust this rate for the preceding crop as above. Also, on sandy soils, use two topdress N applications, one at early tillering and another at early jointing. This can improve yields when N leaching conditions occur. Although yields may not always be improved, this practice can also reduce the amount of N released into the environment and offers the chance to adjust N rates downward if climatic or economic conditions do not warrant the added expense of the last N application. Adjust N rates up or down as you experiment with you particular farm. Avoid excessive N rates in the spring, as it leads to lodging and a reduction in milling properties and flour quality.

Phosphorus and Potassium (P and K)

Phosphorus and potassium fertilizer applications should be based on soil testing. Because 65 percent of the total P uptake and 90 percent of the total K uptake occurs before the boot stage, these nutrients should normally be applied before planting. Split applications (half at planting and half at topdress) of K is recommended on deep sandy soils (greater than 12 inches to subsoil clay). Use of starter fertilizer containing P, especially in reduced tillage systems, is being investigated but not recommended at this time.

Secondary Nutrients

Calcium and magnesium (Mg) are normally supplied when maintaining proper soil pH with dolomitic limestone. If soil pH is adequate but calcium or magnesium are not, applications of fertilizers containing calcium such as calcium sulfate or magnesium such as magnesium sulfate will be recommended.

Sulfur (S) is an essential nutrient that used to be contained in many other fertilizers and in atmospheric deposition or fallout from smokestacks. Today’s fertilizers are largely free of sulfur and sulfur is often scrubbed or removed from smokestack emissions. Therefore, wheat growers now need to make a conscious effort to include at least 10 pounds of sulfur per acre in their fertilizer applications. This can be accomplished either with preplant fertilizer or by including sulfur with topdress N. Because sulfur is mobile in sandy soils, including S with topdress N is the preferable applications timing. In addition, the N:S ratio in plant tissue should be maintained between 10 and 15 to 1 (N:S) and can be easily checked by using plant analysis.

Micronutrients

Micronutrient levels in Georgia’s soils are usually adequate for wheat production unless soils have been over-limed. The two micronutrients most likely to be deficient, and the ones routinely tested for with soil testing, are zinc (Zn) and manganese (Mn). Adequate baseline levels of soil test Zn and Mn should be maintained. If low levels of either of these essential micronutrients are detected, low doses in soil-applied fertilizers should be added to build up the soil test levels. Plant tissue analysis should be used in conjunction with these applications, and foliar Zn or Mn should be used if deficiencies are detected by plant analysis. Attempting to correct low soil test levels with soil-applied fertilizers in one application can be expensive and possibly ineffective and therefore are not recommended. Manganese deficiency occurs most frequently in poorly drained soils of the Flatwoods region. Availability of Mn declines significantly as pH increases above 6.2 to 6.5 in these soils. Deficiencies of other essential micronutrients such as molybdenum, copper, boron, iron, and chloride in wheat are rare.

Doublecropping

Other crops, such as soybeans, are often doublecropped following wheat. Fertilizer recommendations are available to try to supply P and K fertilizer for both crops before planting wheat. These recommendations are often based on crop removal of nutrients by both crops. Because fertilizer nutrients such as K and soil pH levels can drop rapidly on sandy Coastal Plain soils, taking a soil sample after wheat is harvested but before the next crop is planted is encouraged if possible.

Nutrient Removal

Nutrient uptake and removal varies with yield (Table 7). Most fertilizer recommendations account only for nutrients removed in the grain. When straw is also removed, additions of P, K and S should be increased for the following crop. In addition, burning wheat straw, which is not recommended due to loss of organic matter that is potentially valuable to sandy soils, returns P and K but not N to the soil.

Table 7. Nutrient uptake and nutrient removal by wheat at different yield levels. Removal based on grain only

Poultry Litter

Managed properly, poultry litter (manure mixed with bedding material) can be a valuable source of plant nutrients for wheat production. It is most like a complete fertilizer, containing significant amounts of primary, secondary, and micronutrients except for boron. It can be a relatively inexpensive source of P and K, but trying to meet all of the N requirement with poultry litter is not recommended.

On average, broiler litter contains approximately 3 percent N, 3 percent P₂O₅ and 2 percent K₂O (fertilizer value of 3-3-2). Based on this average, one ton of poultry litter contains 60 lb of N, 40 lb of P₂O₅ and 40 lb of K₂O. Based on current fertilizer prices for N, P and K, poultry litter is valued at approximately $25/ton. The nutrient content of litter varies significantly however, depending on moisture content, type of bird, feed ration, and especially storage and handling methods. Therefore, it is highly recommended that litter be analyzed for nutrients by a reputable laboratory before determining application rates and value.

Application rates of poultry litter for fertilizer are usually based on the nitrogen requirement for the crop grown. Poultry litter is also best used as a preplant incorporated, complete fertilizer to supply P, K, secondary and micronutrients to the crop on a timely basis. For wheat, an application of 2 ton/A of poultry litter (preplant incorporated) will supply an adequate amount of fall N and should meet the P and K requirements of even a soil testing low in P and K. The availability of P and K in poultry litter is considered comparable to commercial fertilizer. For N, it is estimated that only 25 percent of the N in poultry litter is readily available. The remainder is in a slower released organic form. Therefore, excessive N in the fall should not be a problem. Release of adequate amounts of N from litter in the spring will depend on a number of factors, especially weather conditions. At the recommended 2 ton/A rate of poultry litter, topdress applications of approximately 50 lb N/A are likely needed. The crop should be monitored in the spring and topdress N applications should be adjusted accordingly.

Planting Date

The optimum planting date for wheat depends upon where it is grown and how it is to be used. Table 8 shows the suggested planting periods for both grain and forage production in the four major production regions of Georgia, Florida, and Alabama.

Wheat planted for grazing should be planted earlier than wheat planted for grain. Wheat planted late does not accumulate forage before winter and therefore does not provide good fall grazing.

Figure 5. Planting regions of Georgia

To obtain high yields and good grazing, plant within the recommended planting dates for your area. Acceptable grain yields have been made when planted later, but yield potential is usually reduced when compared to plantings made during the recommended period. Planting during the recommended period provides adequate time for tillering and root development and reduces the potential for excessive winter damage. Although wheat emerges sooner and the shoot (above-ground portion of plant) develops faster in warm soil (75º to 80ºF), the root system develops much faster and more extensively if the soil is cool (55º to 60ºF).

Wheat planted earlier than the recommended period will be subjected to more disease, Hessian fly damage, and aphids and subsequently to more winter injury. Many wheat varieties require a period of cold temperature (vernalization) before plants form a grain head. Varieties with short vernalization requirements are particularly sensitive to early planting because their vernalization requirements can be met too quickly. These varieties should be planted in the latter part of the recommended planting window.

Planting later than the recommended date can be even more damaging to yield potential. Studies in Georgia have shown planting one week beyond the recommended planting period can reduce yield 20 percent below normal, and planting three weeks late can reduce yield 50 percent below normal. Late-planted wheat will have fewer tillers, be susceptible to winter injury due to a lack of crown development, and develop grain during the warmer, more humid conditions of late May and June. If planted late, the vernalization requirements of some varieties may not be satisfied and the plants will not develop grain heads until late in the season. If planting is delayed more than two weeks beyond the last recommended planting date, use only early maturing varieties with short vernalization requirements.

Table 8. Optimum planting periods

Seedbed Preparation

Wheat performs best when planted on well-drained, fertile soils that have been prepared as a smooth, firm, and weed-free seedbed. Studies show that tillage can greatly affect wheat yields (see the chapter on tillage). Research in the Southeast has consistently shown economical yield responses to deep tillage, especially on Coastal Plain and Piedmont soils, which tend to compact. Deeper tillage allows for easier root penetration, burial of diseased debris, and improved water infiltration. In wet years, low soil-oxygen conditions are enhanced by compacted, dense soils. This condition reduces yield due to detrimental effects on root production a nutrient uptake.

Chiseling, turn plowing, subsoiling or paraplowing results in better yields than disking alone. Pulling a leveling device behind some form of deep tillage such as a chisel plow has been very effective on most soils in the Southeast. Shallow seedbed preparation (accomplished by no more than one disking) is less acceptable on most soils in the region. No-till planting for winter grain production is rarely used in the Southeast.

Planting Method

A grain drill is the best tool for planting wheat. Planting with a drill reduces seed cost, insures better germination, produces more uniform stands, reduces winter injury, reduces competition from weeds, and almost always increases yields. A 10 percent to 15 percent yield increase for drilled versus broadcasted wheat is common.

Although broadcasting and disking can save time, they require more seed per acre and result in many seeds being placed too shallow or too deep for germination and emergence. If you have no choice but to broadcast, increase the seeding rate by 20 percent, set the covering disk to cut about 4 inches deep, and drive at a ground speed of 5 to 7 mph.

Seed Treatments

Fungicide and insecticide seed treatments are an inexpensive but effective method of protecting seed and seedlings from seed and soilborne diseases and early season insects such as aphids and Hessian fly.

Drill-box seed treatments are limited to several types of fungicides. Best performance is achieved when the seed is fully covered at label rates. See the disease and insect sections for specific recommendations.

Seeding Rate

The optimum seeding rate generally varies between 1½ to 2 bu/A for grain and 2 to 2½ bu/A for grazing. Wheat seed size varies greatly from year to year, among varieties, and between seed lots of a variety. Wheat seed may range from 9,000 to over 20,000 seed/lb. These differences exist because the environment in which it is grown primarily determines seed weight or kernel plumpness. An example is provided in Table 9. Notice the differences between varieties. All of the varieties were grown under the same environment.

Table 9. Seeds per pound and test weight of seven varieties of wheat grown in 1995

Seeding based on seeds per acre is much more accurate than seeding based on weight per acre. Generally, a seeding rate of 35 seeds per square foot is desirable. Tables 10 and 11 provide examples of planting rates based on seeds per row foot for different row widths and varying seeds per pound. For this reason, it is important to plant on a seed per row foot basis.

Table 10. Seeds per row foot needed to achieve certain seeds per square foot at different row widths

Table 11. Pounds of seed as determined by row width, seeding rate and seeds per pound

Seeding Depth

Under optimum planting conditions, you can plant wheat 1 to 1½ inches deep and expect to produce a good stand. If conditions are dry, plant the seed 1½ to 2 inches deep. The deeper planting depth will require ¼ to ½ inch of rain to germinate the seed and will ensure that enough water is available to the young seedlings to keep them growing once they germinate and emerge.

If wheat is planted deeper than 2 to 2½ inches, a large portion of the seedlings may fail to emerge, or they may be abnormal once they do emerge (Table 12). This is because many seed lack the food reserves necessary to emerge from deep in the soil.

Care should be taken when planting into dry soils. A light rain on seed planted too shallow may cause the seed to germinate but not provide enough moisture to maintain emergence. Heavy rains on seed planted to deep may prevent the seed from emerging due to soil crusting and compaction. In this case seed may lack the necessary vigor to emerge through the tight crust.

Table 12. Relation of planting depth and seedling emergence*

*Source: S.C. Chambers. 1963.
**Normal: Coleoptile emerges from the soil before the appearance of the first leaf.
***Abnormal: Coleoptile fails to appear, and first leaf emerges from the soil.

Row Width

Yields of more than 100 bu/A have been achieved with 7-inch row spacings. When wheat is planted in 4-inch-wide rows it generally produces 5 percent to 10 percent more grain than wheat planted in 7-inch-wide rows. This suggests that row width should be a consideration when it comes to buying a new drill, but is not a large enough factor alone to mandate the purchase of new equipment.

Weeds affect small grain production in many ways. They compete with the crop for light, water, nutrients and physical space, thereby reducing yields and quality. Weed chaff and seed contaminate harvested grain, resulting in dockage, and the presence of green weeds reduces harvest efficiency and increases grain moisture content.

It is estimated that the total loss from weeds in wheat is more than $29 million in the southeastern United States and more than $850 million nationally.

Weeds in Small Grains: Biology, Distribution and Resistance

Several grass and broadleaf species are common in small grain fields throughout Georgia and the Southeast (Table 13).

Table 13. The 10 most common and troublesome weeds infesting small grains in Georgia, ranked in order of importance

Source: Adapted from Weed Survey-Southern States in Proceedings, Southern Weed Science Society, 1994, vol. 47:273-299.

Broadleaf (dicot) Weeds

Eight of the 10 species are winter annual broadleaf (dicot) weeds. Brassica species, like wild radish, wild mustard, wild turnip (bird’s rape mustard), swinecress, Virginia pepperweed and shepherd’s purse, are the most common broadleaf weeds in small grains in Georgia. Perennial weeds such as curly dock, common mullein and thistles are troublesome, especially in minimum tilled areas. Wild onion and/or garlic are generally less competitive with small grains than wild radish, but they pose grain quality and dockage problems in harvested grain.

Like wheat, most of these weeds germinate, emerge, and grow vegetatively during the fall. Limited growth occurs during winter. Then in late winter or early spring rapid growth resumes, and the plant transitions into reproductive development. Light, water and nutrients are critical during the reproductive phase. Therefore, competition by weeds during this period is very damaging to crop growth and yield. Without good weed control, tillering is reduced, which limits the number of seed heads. Weed competition can reduce head size and grain weight.

Wild radish is generally regarded as a winter annual species, but this weed emerges almost year-around. It is important to plant small grains into a stale or clean seedbed in order to eliminate early-season competition from radish that emerges ahead of cereal planting. Depleting the soil seed bank of wild radish seed will require a year-around effort to prevent seed production. It is noteworthy that the imidazolinone herbicides (Scepter, Pursuit and Cadre) are very active on radish. Because of the persistence of these herbicides, fall suppression of wild radish may result from summer applications of these herbicides to soybeans or peanuts.

Grasses

Several grasses are common to small grain fields in Georgia: Italian (annual) ryegrass, cheat and little barley. Italian ryegrass is the most important grass found in small grain fields. It is extremely competitive with the small grains, causing lower yields, reduced quality, decreased harvest efficiency, and contamination problems. Cheat and little barley are generally not as competitive as ryegrass and infest limited acreage.

Although the 1994 survey shows that Italian (annual) ryegrass is the second most common and troublesome weed in grains in Georgia, it has now become the most difficult-to-control weed for most Georgia farmers, primarily because of control failures with diclofop-methyl (Hoelon). Several factors contribute to control failures (see the Italian ryegrass control section), but one of the more important factors has been the development of Hoelon resistant Italian ryegrass. Italian ryegrass emerges before or with winter cereals and grows very rapidly, competing vigorously with winter cereal grains for nutrients, light, and water. More effective management of Italian ryegrass is essential if Georgia farmers are to grow winter small grains at a profit.

Weed Identification

Accurate weed identification is essential for selecting the most effective and economical weed control tactic. Distinguishing characteristics for some of the most common weeds are shown in Table 14.

Table 14. Weeds common in Georgia winter grain fields

Management and Control

Cultural Weed Control

Cultural weed control plays a major role in reducing weed pressure in small grains. Purchasing certified seed ensures quality, weed-free seed and reduces the potential for the introduction of new weed species. In Europe, corn-cockle (Agrostemma githago) infestations were reduced by over 91 percent through the use of certified wheat seed. The planting of bin-run wheat and rye seed has probably contributed to the spread of wild radish and Italian ryegrass throughout the state. Proper seedbed preparation, fertility, insect and disease control will promote a healthy crop, allowing the crop to shade and out-compete many weeds. Selection of well-adapted varieties and adhering to optimum planting dates will also contribute to a healthy and vigorous grain crop. Cleaning combines will prevent moving weed seed from one field to another.

Grazing small grains that will be harvested for grain may change weed control practices. Cattle often selectively graze on small grain forage and leave the less palatable weeds. Selective grazing may diminish the competitiveness of the crop relative to the weeds so that weeds that are normally considered relatively unimportant may become well-established and reduce grain yields once grazing ceases.

Rotation can be an important practice for weed control. It is often associated with changes in tillage, planting date, crop competition, and herbicide use, all of which can improve long-term weed management. Incorporating canola or a winter fallow into a continuous small grain production sequence can improve Italian ryegrass control. With a winter fallow one can presumably prevent ryegrass seed production and possibly reduce ryegrass seed reserves in the soil. Similarly, canola producers have two options for ryegrass control, preplant applications of trifluralin (Treflan) and post-emergence applications of sethoxydim (Poast) or quizalofop (Assure). Rotations with other winter crops may provide similar benefits to small grain growers.

Mechanical Weed Control

Because between-row cultivation is not possible with drilled small grains, preplant tillage provides the only opportunity for cultivation. Preplant tillage can be used in combination with herbicides to accomplish a "near stale seedbed" condition. Preplant tillage will also minimize problems with perennial species like curly dock. Mowing is not a viable option because most weeds do not bolt until the small grain has begun to elongate. However, mowing may be an acceptable alternative in small grains used for grazing.

Chemical Weed Control

Numerous herbicides are available for weed control in small grains. To maximize performance weeds must be properly identified so that the most effective herbicide can be applied in a timely fashion. Recognition of the following crop stages is critical to effective herbicide use in small grains: seedling stage, tiller stage, jointing stage, and dough stage. Tillers are secondary (axillary) shoots that arise from the base of the plant. With proper fertility management and growing conditions, most plants will form four or more tillers. Once tillered, the plant reaches a resting stage called full tiller, where vernalization is required to cause stem elongation and head formation. This stage of elongation is called jointing. Dough stage occurs as the grain begins to develop, fill and harden. These growth stages are used to determine herbicide application timing.

Broadleaf Weed Control – Phenoxy Herbicides

The phenoxy herbicides, 2,4-D and MCPA, are used for broadleaf weed control in small grains. They have little effect on grasses. They are growth regulators that cause uncontrolled growth in susceptible plants. Most small grains have good tolerance to the phenoxy herbicides, but certain guidelines with respect to crop developmental stage should be followed to minimize injury.

• Phenoxy herbicides should be applied to grain crops that have at least 3 tillers. Applications made before this stage will cause a "rat-tail" or "onion-leaf" effect, where the leaf does not form and unfurl properly. Tiller number can be reduced, the plant may be stunted, and maturity can be delayed.
• Phenoxy herbicides should be applied before jointing. Once the stem begins to elongate (jointing stage) cereal grains can be damaged, resulting in kernel damage and malformed seed heads.

2,4-D is the most active of the phenoxy herbicides. It gives excellent wild radish control, but the potential for crop injury is greater than that with MCPA, especially if it is applied too early. It can be applied from the 3 to 4 tiller stage until jointing begins at rates from 0.5 to 1.5 pints/acre (0.25 to 0.75 lbs-ai) plus a surfactant at 0.25 percent v/v. It is typically more effective on larger plants (3 inches or larger) than is MCPA, but the potential for injury is greater than with MCPA. Application timing is critical to achieve weed control and crop safety. 2,4-D should not be applied with liquid nitrogen! Excessive crop injury is likely to result. The optimum timing for application of nitrogen and 2,4-D typically differs. Mid- to late-December applications of 2,4-D are optimum for wild radish control, but late January to mid-February is optimum for nitrogen fertilization. Therefore, applying the two together in a single pass usually results in either the nitrogen being applied too early or the 2,4-D being applied too late.

MCPA is another phenoxy herbicide labeled for use in small grains. It is less injurious to wheat, but is also less effective on larger weeds. It should be applied very early to small wild radish at rates from 0.5 to 1.5 pints/acre (0.25 to 0.75 lbs-ai) plus a surfactant at 0.25 percent v/v. MCPA can be applied as soon a tiller begins up until full tiller.

Broadleaf Weed Control – Sulfonylurea Herbicides

Three sulfonylurea herbicides are currently registered for weed control in small grains in Georgia. These materials inhibit the production of three essential amino acids in susceptible plants, causing stunting and slow death over a period of 10 days to 3 weeks. With respect to crop safety, sulfonylurea herbicides have a wider range of application timing as compared to the phenoxy herbicides. They can be applied before and after wheat is fully tillered. However, the susceptibility of weeds declines rapidly with increases in age and size of weeds. Rotational crop restrictions exist for most sulfonylurea herbicides. Therefore, check the label regarding rotational restrictions. To maximize weed control:

• Do not apply sulfonylurea herbicides to stressed plants, i.e. abnormally cold, wet or dry weather. Efficacy is greatest in rapidly growing susceptible plants.
• Apply to small weeds and use a nonionic surfactant to ensure adequate coverage.

Express (tribenuron) will provide good control of wild radish but should be applied early for best control. Applied at 1/3 oz. product/A from the two-leaf stage through the third node of joint. Express, applied alone, is marginally effective on large wild radish. Therefore, Express should be tank-mixed with MCPA. When applying with MCPA, follow the MCPA guidelines with respect to timing of applications. This tank-mix is a good, safe alternative to early applications of 2,4-D. Express is only labeled for use in wheat or barley. Do not use on rye or oats.

Harmony Extra (thifensulfuron + tribenuron) will provide good control of wild radish and many broadleaf weeds in wheat. It can be applied from the two-leaf stage through the third node of joint at rates from 0.4 to 0.6 oz. product/A plus surfactant (0.25 percent v/v). Harmony Extra is the product of choice for vetch control. However, it must be applied at the higher rate to non-stressed, actively growing vetch for maximum control. Harmony Extra also can be tank-mixed with MCPA or 2,4-D. Harmony Extra is registered for use on wheat, oats, and barley.

Peak (prosulfuron) is registered for use on wheat, rye, barley, oats and triticale. It has good activity on wild radish, cutleaf evening primrose and wild onion/garlic, and partial suppression of henbit. The rate of 0.5 oz/A is recommended with the addition of a non-ionic surfactant at 0.25 percent v/v. It can be mixed with 2,4-D or MCPA or liquid nitrogen. It should be applied after the third leaf has emerged and prior to early joint.

Broadleaf Weed Control – Buctril (bromoxynil)

Buctril (bromoxynil) is a contact herbicide that is sold alone or in combination with other materials.

It is safe to small grains and can be very effective for early-season control of wild radish. For best results, apply to small weeds having no more than four true leaves. Buctril is often premixed or tank-mixed with MCPA (Bronate) for improved control of weeds such as mustard and wild radish.

Broadleaf Weed Control – Sencor (metribuzin)

Sencor can provide good control of Italian ryegrass, wild radish, and other broadleaf weeds in wheat. See the section on Sencor in the following section on Italian ryegrass control.

Italian Ryegrass Control – Hoelon (diclofop-methyl)

Hoelon is registered for use in wheat and barley. Maximum activity will be achieved if Hoelon is applied to two- to four-leaf Italian ryegrass. Effective control can be achieved at this stage with as little as 1¹/3 pints of product per acre. Once ryegrass has progressed beyond the four-leaf stage, use higher rates up to 2²/3 pints/A. Hoelon can be used pre-emergence in wheat. However, it should be used at the higher labeled rates. Several factors affect the use and performance of Hoelon on Italian ryegrass:

• Hoelon-resistant Italian ryegrass has been identified in Georgia. On these sites, Hoelon will not control ryegrass and its continued use will only make the situation worse.
• Early applications (i.e., December) are much more effective than later applications to fully tillered and hardened ryegrass.
• Environmental stress (i.e., drought or cold temperatures) will significantly reduce Hoelon activity on ryegrass.
• Using crop oil concentrate (COC) at 1 quart/acre will enhance ryegrass control with Hoelon compared with the use of nonionic surfactant.
• Wheat injury, primarily temporary yellowing, has been observed in wheat that was treated with organophosphate insecticides like Di-Syston.
• Do not tank mix Hoelon with other herbicides or liquid nitrogen.
• Do not apply to oats.

Italian Ryegrass Control – Sencor (metribuzin)

Sencor is labeled for use on both wheat and barley in Georgia. It can be used postemergence to wheat or barley after the third tiller provided wheat is planted prior to November 15 and December 1 in the Piedmont and Coastal Plain regions of the state, respectively. Rates are dependent on soil type and crop stage of growth. Therefore, consult the label. Sencor is labeled for control of wild radish. Italian ryegrass does not appear on the label. However, control can be good depending on environmental conditions.

The following precautions should be observed when using Sencor on small grains:

• Do not apply to oats.
• Some cultivars of wheat and barley are sensitive to Sencor. Do not plant sensitive cultivars if you plan to use metribuzin. Consult with your local county extension office and/or the Sencor label for a current listing of tolerant versus sensitive wheat and barley cultivars.
• Carefully read the label to select the proper rate based in soil type and stage of wheat/barley growth.
• Early applications (i.e., four-leaf stage of wheat) are typically more effective on Italian ryegrass than late applications.

Weed Control in Rye and Oats

Relatively few herbicides are labeled for weed control in rye and oats. However, the phenoxy herbicides (2,4-D, MCPA, etc) can be used effectively for broadleaf weed control in rye and oats. Control in these small grains is limited to the phenoxy materials and Peak. The application timings are the same for these crops: three to four tillers to full tiller with rates from 0.5 to 1.5 pints/A. Oats are generally more sensitive than rye. There is nothing labeled for annual ryegrass control. There are 7- and 14-day grazing restrictions for MCPA and 2,4-D, respectively, and a 30-day grazing restriction for Peak.

Liquid Nitrogen and Herbicide Tank-Mixes

Many farmers will apply liquid nitrogen and herbicides in a tank-mix for a single application to cut costs. Tank-mixing is a practical and cost-effective, but it is often a compromise. If herbicides and nitrogen are to be mixed, make sure that application occurs within the optimum application window for both materials. Making applications early may increase weed control, but it may increase crop injury and risk nitrogen deficiency during grain fill. Delaying applications for maximum fertility benefit increases the chance of crop injury with phenoxy herbicides and reduces weed control. Wheat yellowing will often be observed when phenoxy herbicides are applied with liquid nitrogen. This can be minimized by not using surfactants in these mixes unless the herbicide label specifically calls for it.

Herbicide Carryover

Residues that remain from herbicides applied to preceding crops like cotton, peanuts and corn can cause damage to small grains. Although this is not a serious problem, injury is often observed in some fields throughout the state, especially in early-planted grains. Oats generally are more sensitive than wheat, rye or barley. Injury has been observed with Zorial, which has an 18-month rotation restriction for small grains. Also, injury can occur, especially with oats, where Karmex is used as a late-season layby treatment in cotton. Plan your rotations and consult herbicide labels for rotational restrictions.

The herbicides mentioned in this chapter were registered for use in Georgia at the time the chapter was prepared. However, always consult and follow current label directions when using pesticides.

Diagnosis of Disease Problems

Wheat may be affected by a number of parasitic diseases and nonparasitic problems. Parasitic diseases are caused by bacteria, fungi, viruses and nematodes. Nonparasitic problems may be caused by weather extremes, nutritional imbalances, pesticide injury and many other factors.

The first step in diagnosing a problem is to look at the entire field. What is the distribution of affected plants? A general yellowing, stunting, or other symptoms over the entire field is not likely to be a disease. Look to see if the problem is in some type of pattern associated with differences in terrain, soil type or cultural practice that may account for differences in growth. A soil fertility problem often shows up as yellow to light green streaks throughout all or part of the field. Fertility problems may require soil and tissue samples for accurate diagnosis. Distribution of the problem in the field may also suggest the type of disease. For example, a circular to oval pattern is characteristic of a root disease because the disease usually moves only a short distance in one growing season.

The next step in diagnosis is to look for more specific symptoms. Stunted plants or discolored leaves suggest that something could be wrong with the roots. Blackened or discolored areas on the roots strongly suggest a root disease.

Spots on the leaves, stems or heads suggest some type of parasitic disease. You can often find signs of a fungus or bacterium in these lesions which are diagnostic for the disease. These may be bacterial ooze, fungal spores (reproductive units), fruiting bodies containing spores, or the threadlike growth of a fungus.

Accurate diagnosis is important so that the correct control measures can be followed. Accurate identification of the disease may require that a sample be sent to a trained pathologist. Samples should be taken from plants where the symptoms are actively developing. As disease progresses, the amount of dead tissue increases and the diagnostic symptoms are more difficult to see. Be sure you include enough plant material for accurate diagnosis. Do not store samples for prolonged periods in plastic bags. Samples in plastic bags may get overheated if placed in sunlight or secondary molds can grow quickly which obscure the symptoms. Plants that are dry are still useful for diagnosis or isolation of pathogenic organisms. Take the sample to your county Extension agent. Be able to give as much information as possible on cropping history, variety, fertility and pesticide applications, and distribution in the field. Your county Extension agent may send the sample to the Extension Plant Disease Clinic to confirm diagnosis. Photos of disease symptoms can be submitted by Extension agents in Georgia via the Internet using the Distance Diagnostics through Digital Imaging system.

Leaf and Head Diseases

Leaf diseases are especially prevalent in the Southeast because the climate is humid, with frequent rains during the period from jointing to maturity. Prolonged periods of moisture allow disease-causing fungi and bacteria to multiply and spread from diseased to healthy plants. Three foliar diseases caused by fungi are of major importance each year. These are powdery mildew, leaf and glume blotch, and leaf rust. Yield losses up to 30 percent for each disease have been documented in seasons when environmental conditions were favorable. Even in seasons when yield losses are relatively low, test weight may be reduced sufficiently to make the grain unacceptable for milling and baking. Several other leaf diseases may be important in some seasons or on certain varieties.

Seedling Diseases

Seed rots and seedling diseases can sometimes cause stand problems in wheat and other small grains. Symptoms of these diseases are variable, ranging from a rotting of the seed and seedling before emergence to a root and lower stem rot after emergence. Seedling diseases are more common in warmer soils for small grains and thus are more serious in early plantings. Several different fungi cause these stand problems.

They include Rhizoctonia, Pythium, Helminthosporium and Fusarium. Pythium and Rhizoctonia are soilborne. Helminthosporium and Fusarium survive in the soil but are common on seed also. Seed treatment fungicides (Table 15) used in combination with correct planting time and depth of planting help to control soilborne seedling diseases.

Table 15. Fungicide seed treatments for small grains (wheat, oats, barley, rye)

* Examples of formulations in parentheses. Read all labels carefully for use restrictions and most current recommendations.

Seedborne Diseases

Certain fungi that cause diseases of more mature plants may be seedborne. These include Stagonospora nodorum and smut fungi.

Loose Smut

Figure 12. Loose smut

The loose smut fungus (Ustilago tritici) infects the seed, but symptoms are not seen until the following year when the grain head emerges (Figure 12). The fungus remains dormant until the seed germinates. As the plant grows, the fungus grows within it. When the grain head emerges, the flowers are replaced by masses of smut spores. These spores are wind-blown to healthy flowers where infection takes place and the cycle is repeated.

Common or Stinking Smut

This disease occurs infrequently in the Southeast, but it can be severe. Two related fungi, Tilletia tritici and T. laevis, produce black smut spores, which attach to seed during harvest. When the seed germinates, the fungi invade the seedling and grow systemically like loose smut. However, heads develop normally at first. As seed forms, only portions of the seed coat remain. The remainder of the tissue is converted to round "bunt balls" filled with masses of dark spores. This mass of spores contains trimethylamine, a compound that gives the grain the odor of dead fish. These bunt balls break during harvest and contaminate healthy seed with spores. The smut spores can survive in soil in arid regions, but they do not survive in soil in the humid Southeast. Stinking smut only becomes a problem when seed is saved for several years which allows the fungi to build up and when no seed treatment fungicide that controls smuts is used. Use of certified seed prevents the establishment of stinking smut.

Karnal Bunt or Partial Bunt and Ryegrass Bunt

Prior to 1996, Karnal bunt, caused by the fungus Tilletia indica, was not reported in the United States. It was introduced into Mexico about 1970, probably on seed from Asia. Seed with a few bunted kernels were found in Arizona in 1996. Bunt spores are carried on seed and can survive for up to 5 years in soil. The spores do not infect seed or seedlings like other smuts. The dark smut spores germinate on the soil surface when wheat is heading. They produce secondary spores, which are carried by air to the head. If infection occurs during or shortly after flowering, the entire seed is bunted. Later infection results in partial bunting of the seed. Sometimes only pinpoint infections may occur on the seed. Because individual seeds are infected, there may only be one or a few infected kernels per plant.

Suspected Karnal bunt spores were found on wheat seed in the Southeast in 1996, but no bunted kernels have been found. In the Southeast, in Oregon, and in several other countries, spores that resemble the Karnal bunt fungus have been associated with annual and perennial ryegrass seed. The spores found on wheat from the Southeast were from areas where ryegrass is a common weed problem in wheat. These spores of ryegrass bunt are deposited on wheat seed during harvest. Ryegrass bunt has recently been described as a new species, Tilletia walkerii, which is distinct from Karnal bunt. Therefore, Karnal bunt has not been found in the Southeast. Karnal bunt seldom causes significant yield loss, and it can be controlled by the same methods used to control stinking smut and loose smut. Currently Karnal bunt remains a quarantined disease in the U.S. However, it poses no threat to the U.S. wheat crop and efforts are being made to deregulate it.

Soilborne Diseases

Several diseases affect below-ground plant parts of wheat. Unlike many leaf diseases these do not spread over long distances and thus are often found as small areas of diseased plants in fields. They also do not produce many cycles of propagules during the growing season. Because of their limited spread, it may take several consecutive years of wheat production for a soilborne disease to become severe in a field. Soilborne diseases important on wheat in the Southeast are take-all, Pythium root rot, soilborne wheat mosaic and wheat spindle streak mosaic. Several other soilborne diseases may be found in some seasons.

Take-all

Figure 13. Take-all symptoms on roots and stems	Figure 14. Take-all whiteheads

Take-all, caused by the fungus Gaeumannomyces graminis var. tritici, attacks the roots and basal portion of the stem of wheat and other small grains (Figure 13). Take-all is usually observed as scattered circular to oval areas of stunted plants which mature early, resulting in whiteheads which have no or shriveled seed (Figure 14). Whiteheads caused by take-all occur mostly in May (about milk stage) long after any chance of late frost. Take-all diseased plants tiller poorly and are easily pulled from the soil because of a rotted root system. The roots are blackened and brittle and if the lower leaf sheath is peeled back, the basal portion of the stem may be black due to the growth of the fungus. These dead plants may become discolored by harvest time as a result of the growth of dark "sooty" molds on aboveground plant parts. These areas may be excessively weedy due to the poor growth of the wheat. The fungus may also colonize a sizeable portion of the root systems of plants in fields that have no whitehead symptoms.

Surveys indicate approximately 20 percent of wheat fields in Georgia have stunted plants or plants with whiteheads due to take-all. Take-all occurs most frequently in fields having three or more consecutive years of wheat. Triticale, barley, and rye are less susceptible than wheat. Oats are resistant to the disease. Yield losses of 66 percent for wheat, 50 percent for triticale, and 34 percent for barley have been documented.

The fungus infects plants throughout the growing season, but plants infected earlier sustain greater losses. The fungus survives on residue of plants infected during the previous season. Movement of crop debris within fields and between fields should be minimized. In a study in Georgia, crop rotation without wheat for one year reduced disease from 57 percent to 8 percent whiteheads. Two years though may be needed to allow residue to decompose completely so the fungus dies. A one year rotation with canola can also reduce severe take-all to insignificant levels. A summer rotation with sorghum greatly reduces disease compared to a fallow or soybean summer rotation. The take-all fungus is associated with various grassy weeds and volunteer wheat. These infected plants may be important in survival of the fungus in the absence of a susceptible crop. Soil pH above 6.0, and cool wet soils (54º to 61ºF) favor disease, whereas a dry spring can limit the development and expression of whitehead symptoms.

Pythium Root Rot

Pythium fungi are found in all soils and attack a wide range of plants. Diseased roots usually develop soft tan-brown areas. Pythium root rot may cause slight stunting of the plants and reduced tillering. Pythium species reduce yields considerably, especially in reduced tillage systems. Research in Georgia has found that Pythium species are the most common group of pathogenic fungi isolated from wheat seedlings. Within three weeks after planting, 50 percent or more of the wheat plants have roots infected with Pythium species. However, the yield losses associated with this group of fungi on wheat are still unknown. Disease is favored by compacted, wet soils. Early planting when soil temperature is high favors Pythium species, which kill seeds and germinating seedlings. These are most prevalent in the coastal plain.

Soilborne Viruses

Figure 15. Wheat spindle streak mosaic

Soilborne wheat mosaic virus has been known in the Southeast for many years. It seldom causes much damage because most varieties are resistant. Another soilborne virus, wheat spindle streak mosaic virus (WSSMV), was identified for the first time in the Southeast in 1984 at Plains, Georgia (Figure 15). Since then it has been identified throughout Georgia and nearby states. Both viruses are transmitted to wheat by a fungus (Polymyxa graminis) that invades the roots. The fungus causes no damage to the roots but carries these viruses with it. The fungus invades the plant during cool, wet weather (40º to 50ºF) in the fall and early winter.

Plants severely diseased by WSSMV are already stunted and yellowed by mid-to-late February in central Georgia. The yellowing of leaves appears as many very narrow (¹/16 inch or less) stripes. Tillering is greatly reduced and diseased plants mature later than normal. Yield losses from 30 to 67 percent have been documented on susceptible cultivars. The disease appeared because susceptible varieties were planted several consecutive years in the same fields. Precise information is not available, but crop rotation for one or more years is needed to reduce the virus population in the soil. Selection of a resistant variety is critical for control.

Other Soilborne Diseases

Numerous other root diseases occur on wheat, but are of minor importance in the Southeast. These include common root rot, caused by Helminthosporium sativum and Fusarium graminearum, and Rhizoctonia root rot and sharp eyespot, caused by Rhizoctonia solani and closely related fungi. H. sativum causes dark brown lesions on roots and especially the subcrown internode. F. graminearum causes a dry browning of the roots and base of the stem; these plant parts may be reddish due to fungal growth. Common root rot is favored by drought and temperatures from 70º to 85ºF.

Rhizoctonia and related fungi attack the roots and stems of wheat. Rhizoctonia cerealis also causes eyespot lesions on lower leaf sheaths and the base of the stem. The lens-shaped lesions have dark brown borders and tan centers.

Nematodes

Several species of plant parasitic nematodes attack wheat in the Southeast. Root-knot, caused by Meloidogyne spp., is the most common disease. Unless wheat is grown continuously for several years, it is seldom a problem.

Integrated Disease Management

Diseases can be managed by a number of methods incorporating principles of IPM (Table 16). A fully integrated system can reduce input costs and reduce pesticide use. Discussion of these methods follows:

Seed Quality and Treatment

Seed quality is important for several wheat diseases that may be transmitted by infected seed. Seed treatment with carboxin, triadimenol, and difenoconazole provides nearly complete control of loose smut and other smuts. Stagonospora nodorum is transmitted by seed, but the fungus also survives on wheat straw and weeds. Seed treatment will help control leaf and glume blotch when combined with crop rotation. Seed treatment is important in reducing seedling diseases caused by soil fungi.

Wheat and other small grain seed can be treated in one of three ways: commercial treatment, a homemade rotary treater or drill box treatment. Commercial treatment is the most effective. Use of a homemade treater is slow but nearly as effective as commercial treatment. To use this method, fill a 30 gallon barrel about half full with seed, add the recommended amount of fungicide, and rotate 25 times. Seed can be treated several weeks before planting and stored until needed. Drill box treatment is the least effective seed treatment method. To use the drill box method, fill the grain drill about half full, add the required fungicide and stir into the seed. Add the remaining seed and fungicide and stir again. Current recommendations for seed treatment fungicides are given in Table 15.

Crop Rotation

Crop rotation is one of the most effective management tools for control of numerous diseases. Many disease agents survive between wheat crops on wheat residue that was infected the previous growing season. If wheat is planted in the same field the next year, this residue allows the disease agent to infect the next crop. If a crop that is not susceptible to the disease is planted for a period that allows the wheat residue to decompose, the disease agent will die. Crop rotation is most effective for disease organisms that survive in residue and spread only short distances, such as soilborne viruses, leaf and glume blotch and take-all. Rotation is less effective for smuts, powdery mildew and rusts, which are spread over long distances, or the fungi causing Rhizoctonia root rot and Pythium root rot, which survive in soil for long periods.

Disease Resistance

Genetic resistance is the primary means of controlling foliar diseases of wheat (see "Wheat Pest Resistance" chapter). Resistance also does not require additional costs. Very good resistance to powdery mildew and leaf rust has been identified, but these fungi frequently develop new strains. This means that varieties need to be replaced every few years. Resistance to leaf and glume blotch is usually not strong, but varieties with moderate resistance remain so for many years. Moderate resistance to barley yellow dwarf is found in some cultivars. Resistance to soilborne diseases is often not available. However, resistance is available to wheat spindle streak mosaic and soilborne mosaic.

Other Control Practices

Numerous other cultural practices may be effective in controlling specific diseases. Deep tillage may reduce some foliar pathogens, such as Stagonospora nodorum, which survives in residue. However, tillage equipment may also spread certain other diseases such as take-all. Early planting may increase several diseases, because it allows many disease agents to infect plants in the autumn. Early planting favors barley yellow dwarf and take-all. Leaf rust, powdery mildew, and S. nodorum survive through the winter in infected leaves. This allows them to produce spores for new disease cycles early in the spring. Weed control is an important aspect in any management program. It is especially important in the control of volunteer wheat, which may harbor diseases over the summer or allow them to survive in crop rotations not containing wheat. Disease losses can also be minimized by a balanced fertility program that allows the vigorous growth of the wheat plant.

Foliar Fungicides

The use of foliar fungicides and specific recommendations vary depending on the region. Generally, there is no economic benefit from applying fungicides to control powdery mildew and leaf rust when resistant varieties are grown. However, exceptions can occur. Few varieties are highly resistant to leaf and glume blotch and there is some potential for use of fungicides against this disease. Labeled fungicides include mancozeb (Dithane-45 and Manzate 200), benomyl (Benlate) and copper sulfate (Top-Cop, That Big 8), although it seldom performs as well as other materials. Control of leaf and glume blotch with the above fungicides has usually produced yield increases of only 3 to 6 bu/A.

Propiconazole (Tilt) and azoxystrobin (Quadris) are labeled for use on wheat and other small grains. They provide excellent control of rusts, powdery mildew, and leaf and glume blotch. Yield increases of 15 to 20 percent on susceptible varieties have been reported. Several restrictions are required, primarily related to the time when grazing can begin. In 1998 propiconazole received approval in Georgia and other states for a 24C label allowing its application up to the fully headed growth stage. Read the label carefully and contact your county agent or refer to an annually updated statewide pesticide handbook for specific recommendations.

Consider using foliar fungicides when disease occurs early in the growing season, favorable weather conditions for disease development are present, and there is a high yield potential. Foliar fungicides should usually not be applied before the late jointing stage. Application before this stage only gives cosmetic control of foliar diseases and reduces effectiveness later in the season when grain is filling and conditions are more favorable for disease.

Table 16. Effectiveness of control methods for wheat diseases*

* The absence of a number or letter indicates that this control method is not effective.
1 very effective, 2 moderately effective, 3 slightly effective
a delaying time of planting, b deep tillage, c weed control

Wheat is attacked by a number of insects that can cause major losses. The primary insect pests of wheat in the Southeast are aphids and the Hessian fly. Aphids also are very important because they transmit barley yellow dwarf virus. Cereal leaf beetle is a new pest causing increasing levels of damage as it spreads throughout the Southeast. A number of other insects also attack wheat, but these pests occur sporadically. If an insect problem is suspected, proper identification of the pest is crucial. Insect damage can be confused with other types of injury; consequently, scouting and identifying the insect pest are very important.

Pest Biology and Damage

Management Tactics

Plant Resistance

The most efficient and economical method for controlling the Hessian fly is the use of resistant varieties. Many varieties currently available are resistant in the Coastal Plain region. Wheats grown in the Southeast do not contain high levels of resistance to any other insect pest.

Cultural Practices

Several cultural practices can aid in the management of insect pests in wheat. Most insect pests, including the Hessian fly, aphids, fall armyworms, and others can become established in a field on volunteer wheat growing in the summer annual crop before wheat planting. Therefore, control of volunteer wheat by reducing combine losses of grain at wheat harvest and effective subsequent weed control will help in reducing early pest buildup on volunteer wheat. Tillage can have a large impact on fall populations of insects in wheat. Insect populations and damage generally are greater under no tillage than under conventional tillage systems. Table 17 shows the effect of moldboard plowing on fall Hessian fly infestations in wheat. Fall infestations were almost three times greater in the no-till than the plow tillage systems. Plowing buries wheat stubble where Hessian flies oversummer and suppresses volunteer wheat in the late summer. No tillage also may enhance fall populations of aphids, which are attracted to the plant stubble.

Table 17. Effect of moldboard plowing on Hessian fly infestation in the fall and spring

Generally, insect damage is more severe in early wheat plantings. Early plantings allow insects to become established and increase before freezing temperatures limit activity. Damage by many insects can be minimized or avoided by not planting before the recommended planting date in your area.

The effect of planting date on Hessian fly populations in wheat is shown in Table 18. Fall infestations decline in later planting dates. Therefore, damage by the Hessian fly may be minimized by timely planting, but fall damage probably will not be eliminated, particularly in the coastal plain region where activity can occur throughout the winter.

Table 18. Effect of planting date on Hessian fly infestation in winter wheat at Plains, GA

Early planting also enhances fall aphid infestations and infection of barley yellow dwarf virus. Wheat planted early for grazing by livestock is particularly vulnerable to attack by insects, especially the Hessian fly, aphids, fall armyworm, lesser cornstalk borer, and grasshoppers. Either rye, oats or a Hessian fly-resistant wheat should be planted for grazing.

Burning stubble in the spring and fall grazing may reduce insect populations somewhat, but these practices are not very effective in controlling most insects including the Hessian fly. Rotation of wheat with other crops also suppresses insect damage somewhat, but insects are highly mobile; consequently crop rotation may not be as effective as it is for less mobile wheat pests.

Biological Control

All wheat pests are attacked and regulated to some extent by a complex of natural enemies. Several non-stinging, parasitic wasps attack and kill Hessian fly larvae. Platygaster hiemalis attacks Hessian fly larvae in the fall and winter, and several other parasitic wasps attack the spring generation. Because of the number of generations, parasites cannot control the Hessian fly during an outbreak year, but natural enemies probably provide long term regulation of Hessian fly populations.

Aphids also are attacked and killed by parasitic wasps, which cause aphids to become light brown "mummies." Several species of ladybird beetle adults and larvae are important predators of aphids. Ladybird beetle adults move into wheat fields from overwintering sites usually in March or early April where they feed voraciously on aphids and often control aphid infestations. This is too late to prevent transmission of barley yellow dwarf virus but may prevent direct aphid injury to developing grain. Hover fly larvae also can be found eating aphids in wheat fields.

Cereal leaf beetles are controlled by parasitic wasps in the northern United States. In 1995, the USDA Animal and Plant Health Inspection Service began releasing a stingless wasp, Anaphes flavipes, that attacks cereal leaf beetle eggs. Nursery plots also have been established to release larval parasites, primarily Tetrastichus julius. Hopefully, once established, these parasites will keep cereal leaf beetle populations below economically damaging levels. Ladybird beetles are also important predators and can destroy many eggs and larvae.

True armyworms and most other wheat pest are attacked by a complex of parasites, predators, and pathogens that prevent their populations from reaching economic levels in most years. Pathogenic fungi are especially important in suppressing populations of chinch bugs, grasshoppers and aphids. These fungi require wet, humid conditions to develop, consequently, populations of these pests typically are worse in dry than wet years.

Insecticides

Insecticide use in small grains is increasing as wheat is grown more intensively. The granular insecticides DiSyston and Thimet (phorate) applied at 1.0 lb active ingredient/A at planting are effective in controlling Hessian flies for about 45 days on susceptible varieties. These insecticides, however, must be applied in-furrow at planting. Broadcast applications are not effective. Although insecticides applied at planting may control initial Hessian fly damage, these treatments will not prevent reinfestation by subsequent generations during the winter and spring. Foliar applications of insecticides in the spring for Hessian fly control are highly variable in effectiveness and are not recommended.

The incidence of barley yellow dwarf also may be reduced by controlling aphids in the fall and late winter using foliar insecticides or by using an insecticide seed treatment at planting. The cost of these treatments should be weighed against the historic or expected loss from aphid infestation and barley yellow dwarf infection. Except for the Hessian fly and lesser cornstalk borer, all other insect pests including aphids can be controlled by applying foliar insecticides when population numbers exceed economic thresholds (Table 19). Consult the Georgia Pest Management Handbook, the Alabama Small Grain Insect, Disease and Weed Control Recommendations, or your local county Extension office for specific insecticide recommendations.

Table 19. Damage symptoms and economic thresholds of insect pests of wheat

Summary of Management Practices

1. Avoid continuous planting of wheat in the same field.
2. Select a Hessian fly resistant variety.
3. Control volunteer wheat.
4. If possible, chisel plow and disk harrow fields to bury wheat debris.
5. Do not plant wheat for grain before the recommended planting date for your area.
6. Consider planting rye, oats, or ryegrass instead of wheat for grazing.
7. Granular insecticides applied in-furrow at planting should be considered for Hessian fly susceptible varieties. Do not apply DiSyston 15G to wheat grown for grazing.
8. Scout fields (sample 5 to 10 sites per field) for insect pests, except Hessian fly, and control with foliar applied insecticides when numbers exceed treatment thresholds (Table 19).

Varietal selection should be based on many factors including resistance to insects and diseases. Breeders traditionally add the best combinations of pest resistances to the highest yielding parents, providing each new variety with the most desirable characteristics available. When appropriate and possible, combine pest resistance with other control practices, such as crop rotation, because they tend to complement and enhance one another. Use of resistant varieties is preferable from both economic and environmental viewpoints and has a sound history of successes.

Types of Resistance

Disease Escape

Although not a true type of genetic resistance, certain characteristics of a variety can reduce or prevent pest damage. Some varieties mature early enough to avoid damage from pests. This escape mechanism is effective during many seasons with diseases such as stem rust caused by Puccinia graminis. Dry spring weather or the absence of infection-promoting dews slows the progress of leaf and glume blotch caused by Stagonospora nodorum and leaf rust caused by Puccinia recondita. Early maturing varieties often have a better chance of escaping losses. Planting late in the recommended period when temperatures are cooler reduces the likelihood that aphids will transmit barley yellow dwarf virus to seedlings and generally avoids seedling damage by insects.

Genetic resistance to pests may occur in several different forms:

Hypersensitivity

Many plants respond to infection with a biochemical reaction that kills the cells surrounding the infected area and inhibits the further development of the causal microorganism. This hypersensitive resistance has been used extensively for resistance to rusts and powdery mildew (Blumeria graminis). A related phenomenon characterizes plant resistance to the Hessian fly (Mayetiola destructor). Fly larvae that feed on resistant wheat plants are killed by a chemical in the plant before they can cause any damage.

Tolerance

Tolerant plants have the capacity to yield well in spite of infection by disease or infestation by insects. This tolerance protects the plant from the damaging effects of the pests even though it is severely infected. Protection derived from this mechanism is difficult to identify. Barley yellow dwarf is a disease to which some varieties exhibit tolerance. However, plant tolerance can be overwhelmed by severe disease infection or very large pest numbers.

Partial Resistance

Several to many genes control a complex sequence of responses to infection in some plants, which serve to slow the development of a disease such as leaf and glume blotch. This resistance may also restrict the size of the area infected, lengthen the reproductive cycle of disease-causing micro-organisms, and greatly reduce the number of fungal spores produced. Partial resistance slows disease development enough to allow the plant to mature without suffering significant yield loss. This slow resistance often lasts longer than the hypersensitive type, thus prolonging the useful life of a variety.

Resistance to Specific Pests

Leaf Rust

Leaf rust populations comprise several different strains or races, which differ in their capacities to survive on various wheat varieties. Thus, when a new rust resistant variety is introduced, it provides protection from losses only until the rust population changes. Then a new race often builds up that overcomes the plant’s resistance and causes significant damage. This limits the useful life of a new variety to as little as two to four years in the Southeast. Breeding programs must maintain a continuous effort to incorporate new sources of resistance to leaf rust. Slow rusting wheat types (partial resistance) have been discovered which may also last longer than the conventional types with one or two effective genes. These are genetically complex and hence difficult to incorporate quickly into new varieties. Generally, the newest varieties should provide the best levels of resistance to leaf rust. Data from comprehensive regional surveys of the rust population guide selection and use of new sources of resistance.

Powdery Mildew

Powdery mildew, like the rusts, is caused by a fungus that readily evolves new races that can quickly render resistance ineffective. Several single genes have been identified and used in the Southeast to provide protection, but most have eventually been overcome by new races. Yield losses of 34 percent have been documented. Partial resistance, sometimes called "slow mildewing," may be an important type of resistance that would not be outdated by the occurrence of new races. New varieties feature the most current and effective genes for resistance to powdery mildew.

Leaf and Glume Blotch

Resistance to leaf and glume blotch is the partial type which slows the infection process, delays the time until lesions and new fruiting bodies form, and reduces the amount of spores produced. Varieties such as Gore with this type of resistance slow the development of the epidemic and protect the plant from damage. The level of resistance remains virtually constant over time.

Hessian Fly

Genetic resistance to Hessian fly is available and can effectively eliminate economic losses. Unfortunately, this type of resistance is often rendered ineffective by new biotypes of the insect, which are similar to races of plant disease agents. Resistance genes offer differing levels of protection based upon the predominant biotypes in the area. Gene pair H7H8 currently offers good protection in the Southeast. New genes are being incorporated into varieties as shifts in the Hessian fly occur. Most varieties now grown in the Southeast are resistant.

Barley Yellow Dwarf

Resistance to barley yellow dwarf virus is often difficult to determine, especially in wheat, because symptoms are variable, and sometimes infected plants may exhibit no or only mild symptoms. Some wheat varieties exhibit a degree of tolerance to barley yellow dwarf. Yield loss is not always associated with the severity of symptoms. The best method to determine tolerance to barley yellow dwarf virus is to compare the grain yield of infected plants of a variety with those protected with insecticides to prevent or reduce transmission of the virus by aphids.

Crop rotation has long been a valuable management practice to control weeds, insects and diseases. Many plant pathogenic fungi and bacteria survive on infected debris of a crop. When the plant tissue decays, the pathogens also die. Crop rotation often results in the loss of the preferred host or the only host for an insect or plant pathogen. Pest populations then decline below threshold levels needed to cause economic damage. Weeds may be less able to compete for nutrients or to thrive in low light conditions under a dense crop canopy of rotational crops. In most cases, the longer the period between planting of the same crop, the better the pest control. Crop rotation also can have beneficial effects on soil tilth, soil organic matter and plant nutrition. The best example of a nutrient benefit is the fixation of nitrogen when legumes are grown and the soil nitrate levels available to a following crop increase. Unfortunately, rotation with a different crop each planting cycle is not always feasible. Much of the small grain acreage in the Southeast is grown as part of a doublecropping system. Therefore, rotations must be planned for two crops a year in many cases. In the past, an option was to leave fields fallow to manage pests and rebuild soil structure. The economic pressures of modern agriculture make this less of an option. The optimum is to grow a diversity of crops with a positive economic benefit derived from each crop in the rotation.

Below is a summary of recommendations based on current research for management of small grain pests with crop rotation and soil management. All crops in a rotation benefit from reductions in pest populations.

A three year study of crop rotation effects on pests using the wheat:soybean doublecropping system was conducted at the Southwest Branch Station at Plains, GA. Twelve rotation sequences were planted. Canola was substituted in some rotations for wheat and grain pearl millet was planted in place of soybean in some rotations. One of the diseases studied was take-all root rot of wheat (see "Diseases of Wheat" chapter). Take-all often becomes severe when wheat is planted more than two consecutive years. Crop rotation is the primary means to control this disease. One year of canola between wheat crops reduced take-all severity to a low level, and grain yield was the same as wheat with no take-all. Soybean as a summer crop does not reduce take-all, but sorghum reduces the disease in a following crop of wheat. Take-all damage after pearl millet was the same as after soybean. Rye and barley are less susceptible to take-all than wheat, but wheat sustains as much damage after these crops as after continuous wheat. Oats is the only small grain that can be rotated with wheat to reduce take-all. Wheat should not be grown for more than two consecutive years. Both canola and pearl millet are compatible with the wheat:soybean system. Grain pearl millet has potential for the expanding poultry industry in the Coastal Plain. The most critical time in the cropping system is the planting time for canola, which with current cultivars, must be completed by November 10 in the Coastal Plain. Therefore, choice of a soybean cultivar in the proper maturity group is important. Pearl millet matures in September, so planting of the autumn crop is more flexible. Continuous wheat also favors soilborne wheat mosaic and wheat spindle streak mosaic (see "Diseases of Wheat" chapter).

Hessian fly is the major insect pest of wheat. The primary means of control is plant resistance, but crop rotation also is useful if susceptible cultivars are planted. Other small grains are moderately susceptible and can serve as a source of Hessian fly for wheat. Hessian fly declined when canola was rotated with wheat.

With the increase in cotton acreage, tests have been conducted to determine if planting cotton after wheat is possible. In Florida, early to medium-maturing cotton cultivars planted after wheat have yielded 1,000 lb lint/A. Availability of irrigation and tillage need to be considered as part of cotton management after wheat. Cropping systems using rye or other small grains as a winter cover crop or for winter grazing followed by full-season corn, soybeans or cotton are options. Small grain winter cover crops can reduce nematode populations which affect summer crops. No-till cotton planted into rye residue produced three bales of cotton per acre in large plots in Piedmont soils at Watkinsville, GA. Intercropping cotton into wheat prior to wheat harvest has been tested in South Carolina. With proper equipment and row spacing, cotton was successfully planted into wheat. The expansion of vegetable acreage also provides a system that may include rotations with wheat or other small grains.

Fusarium head scab of wheat causes direct losses in yield and seed quality but is most important because of toxins that affect humans and animals produced by the fungus. The same fungus causes a stalk rot of corn. Scab has become a serious problem in the upper Midwest in recent years because of higher levels of precipitation and use of reduced tillage following corn. Wheat scab has not been as serious in the Southeast. However, the potential for scab is present whenever wheat follows corn or possibly sorghum. Corn and sorghum residues should be thoroughly incorporated into soil prior to planting wheat.

If wheat or other small grains are planted in consecutive years, deep tillage before planting reduces surface residue that harbors Hessian fly pupae and pathogens such as Stagonospora nodorum. Deep tillage also incorporates grassy weeds that harbor aphids that damage seedlings directly or transmit barley yellow dwarf virus.

Wheat must be harvested with minimum losses to realize the maximum return from all production practices. Minimum losses are achieved by harvesting on time with proper combine adjustments and operation. If the grain contains excess moisture, it must also be dried for safe storage.

Combine Functions

Figure 22. Threshing, separating and cleaning components of a typical combine

Figure 23. The effect of fan adjustment on cleaning losses

A thorough understanding of the combine components is required to make the proper adjustments for satisfactory operation (Figure 22). By studying this diagram, you should be able to understand the general functions of the combine and why adjustments must be made for various conditions.

The header gathers, cuts and conveys the grain and straw into the combine, then into the cylinder. All the grain and straw must then pass between the cylinder and concave, where the grain is threshed from the heads. Some of the threshed grain will fall through the concave onto the cleaning shoe, which is made up of a chaffer (coarse sieve) and a sieve (fine sieve).

The straw and the grain that remains in the straw then move to the straw walker (rack). The reciprocating motion of the straw walker causes the straw to move across the straw walker and out the back of the combine. As the straw moves over the straw walker, the threshed grain is vibrated out of the straw and conveyed to the chaffer where it joins the threshed grain coming directly from the cylinder and concave.

The grain contains a lot of trash and broken straw when it reaches the chaffer. The chaffer is a coarse sieve that is usually adjustable. The chaffer shakes in a back-and-forth motion, which moves the material riding on the chaffer out the back of the combine. Grain and heavy small trash fall through the chaffer onto a sieve that is finer than the chaffer. The sieve also shakes, causing the material on the sieve to move to the rear. The material passing over the sieve is called "tailings" and is returned by an auger and elevator to the cylinder for additional threshing.

A fan blows air up through the sieve and chaffer to remove light trash and to aid the rearward movement of the material on the chaffer and sieve. Excess cleaning air will blow grain out the rear of the combine, and too little air may cause the cleaning chaffer to clog and pass grain out the back of the combine (Figure 23).

Another method of threshing is to place one or two rotors (rotating cylinders) parallel or transverse to the flow of the crop through the threshing area. Threshing takes place as the material moves towards the rear in a spiraling cylindrical mass between the rotor and the rotor cage.

The crop makes several revolutions around the chamber while passing through the machine but at a slower speed than the rotor. As a result, the rasp bars make several contacts as the crop is moved past the concaves. Thus, the rotor uses a rubbing, rolling action in threshing. Separation of the grain from the straw is aided by the centrifugal force set up by the rotors. Nearly 85 percent of the threshed grain falls through the concave grate. The remainder of the grain, along with the straw, continues the rearward spiraling motion into the separation area of the rotor cage.

Combine Adjustments

It is evident that one adjustment can affect grain losses in several ways. The main combine adjustments are the reel position and speed, the cutter bar height, the cylinder speed, the concave clearance, the chaffer and sieve openings, and the fan and windboard settings. The owner’s manual will give the initial settings for all grain; however, the following adjustments are for small grain in average conditions.

The final adjustments must be made in the field because they will be affected by such things as grain moisture, the condition of the straw, the quantity of weeds or green material, the kind of grain and yield.

Reel

The reel shaft should be 8 to 12 inches forward of the cutter bar with the top of the reel slats (boards) at a height just below the grain head. The reel tip speed should be 25 percent faster than the ground speed. For lodged wheat, a pickup reel should be used; its height should just clear the cutter bar.

Cylinder Speed

Tip speed of 5,700 to 6,500 feet per minute is recommended for wheat. The cylinder revolutions per minute (rpm) will vary with its diameter as follows:

The cylinder speeds required for an initial cylinder tip speed of 6,000 feet per minute with various cylinder diameters used in new combines are shown in Table 20.

Table 20. Suggested initial cylinder speeds

Figure 24. The concave clearance

Measure opening perpendicular to sieve finger

Figure 25. Measuring the chaffer and sieve opening

Figure 26. The effect of harvesting time on yield of wheat

Concave Clearance

Concave clearance should be ¼ to ½ inch with an initial setting of ³/8 being suggested (Figure 24). Consult your owner’s manual for rotor speeds in rotary combines.

Chaffer

Set chaffer opening to ⁵/8 inch (adjustable type) measured perpendicular to the tip of the movable finger (Figure 25).

Sieve

Set sieve opening at ¼-inch (adjustable type) measured perpendicular to the tip of the movable finger (Figure 25).

Fan

Inlet 75 percent open with windboard directing air to the front half of the chaffer and sieve. Note: On models with an adjustable speed fan, start with an initial fan speed of approximately 65 percent full speed.

Ground Speed

Three miles per hour maximum.

Combine Losses

The grain tank should be checked periodically, along with the combine losses on the ground, to make sure the combine is adjusted properly. Excess trash in the grain tank means improper fan, chaffer and/or sieve adjustment. If you try to get the grain too clean, you will increase losses by blowing grain out the back of the combine. Also, check the tailings elevator for the quantity of grain being returned to the cylinder. Excess tailings can result in cracked grain.

Field losses may be divided into two categories: preharvest and harvest (machine). Preharvest losses are defined as those shatter losses on the ground and the loss of dry matter due to birds, wildlife, weather, and natural respiration. Figure 26 illustrates the effect of time on these preharvest losses.

Harvesting losses are those losses caused by the combine. Some harvesting losses are unavoidable, but excessive losses are due to improper combine operations and/or adjustments. Modern combines are capable of harvesting 97 percent to 98 percent of the small grain.

The harvesting machine losses can be divided into the following categories:

Header Losses

The grain lost by rough handling by the cutter bar and the reel, and grain not cut by the cutter bar because of excessive cutting height or lodged grain.

Cylinder Losses (threshing loss)

The grain lost over the straw walker because of unthreshed heads and/or cracked grain from high cylinder speeds and/or insufficient concave clearance.

Combine Leakage Losses

Grain lost through cracks and clean-out doors in the bottom of the combine.

Straw Walker Losses (rack or separating losses)

Threshed grain lost over the straw walker because of excessive straw feed rate caused by excessive ground speed and/or low cutter bar height.

Chaffer and Sieve Losses (shoe or cleaning losses)

Grain lost over the chaffer and sieve because of excess fan air (grain blown over), excess material on the chaffer (straw broken up too much by the cylinder because of excessive speed and/or too little concave clearance), or because the chaffer and sieve are closed too much (material riding over the chaffer out the rear of the combine and excessive amount of tailings returned to the cylinder).

Checking Losses

Field losses can be determined by counting the kernels of grain on the ground for a given area (Table 21). The number of kernels per square foot should be counted in several places and averaged for more accuracy. There are usually more kernels directly behind the combine than across the rest of the swath; therefore, when determining threshing losses, the kernels counted behind the combine must be taken across the entire swath width (Figure 27).

Figure 27. Locations for checking combine losses

Table 21. Small grain loss chart

Combine losses can be checked by the following procedure:

1. Disengage the straw spreader if one is being used.
2. Harvest a 300-foot-long strip where the grain is typical of the entire field.
3. Stop the combine and let it clean out.
4. Mark the position at the rear of the header and just in front of the combine rear wheels.
5. Back the combine one length and check for losses as described below and indicated in Figure 27.
6. Check for any leakage loss at the previously marked position in front of the rear wheels. A heavy streak of grain indicates a grain leakage. Repair the leakage hole in the combine and restart the loss testing at Step 2.
7. Count the shattered kernels on the ground in a 10 square foot area across the width of the header in front of the combine in the uncut grain area. Enter the total number of grains counted in Table 22, Column 1, Line A. This represents the preharvest loss.
8. Count the total number of kernels on the ground including the kernels in any uncut heads in a 10 square foot area across the width of the header at the previously marked position at the rear of the header. Enter the total number of kernels counted in Table 22, Column 1, Line B. This represents the header losses plus the shatter losses.
9. Count the total number of kernels on the ground including the kernels in any uncut or unthreshed heads in a 10 square foot area across width of the header in its backed position. Keep a separate count of the kernels in any cut but unthreshed heads (cylinder loss) and enter the number of kernels found in the heads in Table 22, Column 1, Line C. Be sure also to include these in the total count, and enter the total number of kernels in Column 1, Line D.
10. Complete Table 22 to determine the losses. Complete each line in Column 3 by dividing the number of kernels found in Column 1 by the number of square feet from Column 2. Complete Lines A, B, C, and E in Column 4 by entering the kernel count for the specific small grain from Table 21. Complete Lines A, B, and C, in Column 5 by dividing the average number of kernels from Column 3 by the number of kernels per square foot equivalent to 1 bushel per acre from Column 4. Complete Lines E, F, G, H, I and J, as indicated in the table.

The cylinder loss (cut but unthreshed heads, Table 22, Column 5, Line C) should not exceed 0.5 percent of the yield, and the total machine loss should not exceed 3 percent of the yield. If the total machine losses are over 3 percent, the appropriate adjustments should be made and the losses remeasured.

Table 22. Grain loss data

Drying and Storage

Wet grain in grain bins must be dried to be stored. Small grain normally contains a relatively small amount of excess moisture. Bin drying using the layer-in-bin method is generally the most economical. A volume greater than 25,000 bushels is generally required before a batch or continuous flow dryer is indicated.

Equipment for Layer-in-bin Drying

Adequate drying equipment is necessary to satisfactorily dry grain. With the larger harvesting machines commonly available, drying speed is the main problem with in-storage or layer, drying. Speed is achieved by using either larger quantities of air, or more heat, or both. Heat will overdry the grain, so large quantities of air are necessary for selecting equipment for satisfactory and economical operations.

Table 23. Typical drying equipment data for grain bins (all specifications from one manufacturer)

* 16-foot depth from drying floor to eaves.

Fan

The fan should provide at least 25 cubic feet per minute (cfm) per square foot of bin floor area at a static pressure of 2 inches (water column). Typical total quantity of air for various bin sizes is shown in Table 23.

Heater

The heater should be capable of heating the air delivered by the fan 15ºF with the bin full or with the fan operating against 3 inches static pressure. (Caution: As the bin is filled, the fan forces less air through the greater depths and less heat is needed.) The heater rating to give a 15º heat rise is shown in Table 23.

Roof Exhaust

The bin should have 1 square foot of open exhaust area for each 1,000 cfm, or one manhole for each 3,000 to 4,000-cfm fan capacity. Because one manhole is standard equipment on a bin, extra manholes must be purchased with all drying bins 18 feet or more in diameter. Inadequate air exhaust area will restrict the fan and reduce air flow (drying capacity). See Table 23 for the exhaust area needed for various bin sizes.

Air Entrance

Entrance collars, the fan-to-bin transition duct, and the drying floor supports adjacent to the fan should not excessively restrict the air entrance to less than 1 square foot open area for each 1,500 to 2,000 cfm. Do not place concrete blocks in front of the air entrance. Use special steel floor supports in front of the fan entrance. If the overall drying floor is supported with concrete blocks, only heavy-weight concrete blocks that have been fully cured should be used.

Table 23 summarizes typical drying equipment specifications. It is much easier and cheaper to purchase equipment meeting these specifications than to find that the equipment is unsatisfactory or does not perform as desired.

Drying For Immediate Sale or Storage

If the crop is being dried for immediate sale or for short-term storage (30 to 60 days), the moisture content should be reduced only to the extent necessary to meet market grade.

Because grain standards no longer relate moisture and grade, determine what is the maximum moisture acceptable without dockage. For example, if you determine wheat can be sold without dockage at 13.5 percent, then dry only to that level. Any further drying is money lost. If the grain is to be stored for very long, it must be dried further. Maximum grain moisture contents considered safe for 12-month storage for all small grains are 12 percent in northern Georgia and 11 percent in South Georgia. Moisture contents lower than these would, of course, be safer. The maximum storage moisture contents require management and aeration during storage. Reduce by 1 percent for poor quality grain, such as grain damaged by blight, drought, etc. Reduce by 2 percent for non-aerated storage.

Air Required for Drying

Because very little heat is used for in-storage drying, the excess moisture is removed mainly with natural air. The air flow must be sufficient to remove the excess moisture before the grain molds or deteriorates. Higher moisture content in the grain requires more air flow. The minimum air flows for various moisture levels are shown in Table 24.

Table 24. Minimum air flow rate for drying (cfm/bu)

Air Flow Through Grain

Increasing the depth of grain in a bin allows less air flow because of the higher static pressure from the added grains. Less air flow means longer time required for the drying front to move through the wet grain. Larger, more powerful fans provide more air than smaller, lower horsepower fans; but once the fan is purchased and installed the air flow rate per bushel of wet grain is regulated or maintained by varying the depth of wet grain in the bin in relation to the total grain depth. Minimum air flow rates per bushel and maximum grain depth recommendations for in-storage drying are shown in Table 25. A grain bin equipped with a drying fan of the recommended size and sufficient roof exhaust (manholes) will give the minimum air flow for any moisture condition at the maximum first-layer depth shown in Table 26. When this layer becomes dry, another layer two-thirds as deep as the previous layer can be added on top of this first layer. As each layer becomes dry, another layer is added; but the depth of each succeeding layer should be reduced by approximately one-third to maintain the same air flow per bushel of wet grain.

Table 25. Minimum air flow rates and maximum first-layer depths for in-storage drying (Drying depths below are for the recommended fan sizes shown in Table 22.)

*Depths must be reduced if grain contains fines.
**Pressures given include 0.25 inch for duct losses.

Table 26. Equilibrium moisture contents of grain*

*Data not available for triticale

The rule of reducing the depth of each succeeding layer by one-third assumes that the maximum depth is added each time and that the initial moisture content remains constant. If less than the maximum depth is used or if the grain for the upper layer has a sufficiently lower moisture content, the one-third reduction in successive layer depths may not be necessary. Actually, the maximum quantity of grain can be dried in a bin when each layer contains only the quantity that can be dried each day (daily fills); but this usually requires extra work, because the loading auger must be moved more often to fill each bin every day and each layer must be leveled in order to dry. When loading and leveling, try to spread any trash or foreign material uniformly so as not to block the air flow.

If your fan is smaller than that recommended in Table 23, the depth of each layer of wet grain must be reduced to maintain the necessary air flow to prevent deterioration.

There should never be more wet grain in a bin than can be dried in four days. The depth of wet grain remaining in a bin can be determined by probing the grain with a ¼ inch smooth steel rod. A definite change in the resistance to the penetration of the rod will be noted when the end enters the dry grain. Caution: Each layer must be leveled before drying for all grain. A mechanical grain leveler is very useful for this purpose.

Drying Heat

Layer drying is accomplished with relatively little heat. During warm sunny days only unheated natural air is used. During periods of high humidity and at night, a small quantity of heat is used to achieve the desired rate of drying. The quantity of heat used affects both the rate of drying and the final moisture content because the lower layers continue to dry until they reach equilibrium with the drying air. This final moisture can be estimated by referring to Table 26. The ideal relative humidity for layer drying is 50 percent to 60 percent to achieve a good storage moisture content. This ideal 50 percent to 60 percent drying humidity is achieved by using natural, unheated air during fair days and a 15º to 20ºF heat rise at night and during cool, damp days. A 15º heat rise means that it is 15º warmer under the bin than outside. Do not check the temperature in the top of the bin, because evaporative cooling occurs as the air passes up through the wet grain and picks up moisture.

Higher heat will speed drying but will overdry the grain. The amount of overdrying can be estimated by referring to Table 26 after determining the relative humidity of the drying air by the following rule: Each 20ºF of heat rise will cut the relative humidity in half. Example: A 20ºF heat rise during a damp night with 100 percent relative humidity (rh) gives 50 percent relative humidity under the bin (100 percent rh @ 60º + 20º = 50 percent rh @ 80º).

As the bin is filled, the added grain depth increases the static pressure the fan operates against. This increased static pressure reduces the total air flow, causing an increase in the heat rise or temperature under the bin. The increased temperatures will further lower the humidity, causing the bottom layers to continue to dry and delaying the drying of the top layer. To maintain the original moisture content in the lower layers of grain, the heat input (Btu) must be reduced as the bin is filled.

The heat is adjusted by varying the gas pressure on the burner and/or changing the orifice (nozzle) size that the gas passes through. Some drying fans and heaters have a "high and low" valve; this valve should always be in the low position for layer drying.

Tips for Drying and Storage

1. Purchase adequate drying equipment.
2. Check bins for holes or gaps that should be sealed before the grain is loaded.
3. Thoroughly clean the grain bin to remove leftover grain and debris.
4. Apply empty bin treatment or fumigate as necessary to eliminate any leftover insects.
5. Clean grain to remove excessive fine particles if necessary.
6. Dry grain to recommended moisture content before storage or use layer method to dry grain.
7. Apply a grain protectant insecticide as grain is loaded into bin. If grain is to be dried in the bin do not apply a protectant insecticide because it will break down with heating. In this case it will be necessary to transfer the grain out of the bin, and treat with a protectant as it is loaded back in.
8. Start the fan as soon as the floor is covered with grain.
9. Keep all exhaust hatches open when fan is operating.
10. Don’t put more wet grain in the bin than the amount that can be dried in four days.
11. Level each layer of grain, including the uppermost layer of grain.
12. Don’t let high-moisture grain heat from respiration.
13. Dry in both bins at the same time for maximum drying speed when two bins are equipped with only one fan.
14. Begin to aerate to cool grain as soon as possible after drying.
15. Continue to cool at every opportunity when the weather is dry and cooler than the grain until grain temperature is below 55ºF.
16. Continue to aerate periodically during storage.
17. Do not freeze grain.
18. Do not aerate during warm humid weather after the grain is cold. This will cause moisture to condense in the grain mass.
19. Probe and inspect grain during storage for heating, damage, and insects. Sample every 20 days in spring, summer and fall; every 30 days in winter. Take at least five samples from each bin. If insect infestations are found, grain should be used as quickly as possible (on-farm feed) or fumigated to allow for continued storage.

Consult the Georgia Pest Management Handbook or the Alabama Cooperative Extension Service IPM-330, Stored Grain Insect Control Recommendations for specific insecticide recommendations.

Soft red winter wheat grown in the southeastern United States is suitable for a wide variety of products. The flour of soft red wheat is finely granulated, low in protein, and has low absorption (water holding capacity) with weak gluten features, making it uniquely suited for a variety of products. In the Southeast, soft wheats primarily are used for all-purpose flour. Soft red wheat flours are preferred in cookies, cakes, crackers, pie crusts, donuts, biscuits, flat breads, batters, gravies, soups, ice cream cones and starches. At least eight soft wheat flour types are used, which includes three cake flours, two cookie flours, and cracker, pastry and thickener flours.

Crackers and flat breads rely on protein strength for structure. The balance between protein strength and protein quantity is very important in determining end-product acceptability. Cultivars that have the stronger protein type are better suited for cracker production. The increased number of major Southern soft wheat cultivars has broadened the variability of wheat protein quality or strength.

Soft wheat quality evaluation is separated into two distinct processing steps: milling and baking (Table 27). Milling quality criteria include bran endosperm separation, kernel hardness and flour yield. Flour yield is the most important trait for milling quality evaluation. One hundred lb of wheat should yield more than 70 lb of white flour. Baking quality refers to the potential of flour to contribute to the acceptability of a baked product and is measured by flour protein quality and quantity, flour viscosity, ash and flour color. Generally, good quality soft wheats should have high flour yield, low protein content, high softness equivalent (soft kernel) and low water absorption (AWRC). Soft texture kernels result in high flour yield. Low water absorption improves flour-baking quality. Cookie diameter gives an evaluation of the actual baking performance of flour.

Table 27. Soft wheat quality traits for cultivars grown in the Southeast

1 Higher or lower than the standard check. Letter ranking from A to F (excellent to very poor).

Environmental conditions greatly influence milling and baking quality, especially kernel hardness which results in lower break flour yield, coarser flour, higher protein content and lower water absorption. Field sprouting of wheat, which occasionally occurs in the Southeast, can be a serious problem for milling and baking quality. Sprouting causes particular problems for wheat that would otherwise be used for cracker production. Sprouted grain has enzyme activity that interferes with the fermentation process which makes it unsuited to cracker dough batch development.

Flour mills in the Southeast grind millions of bushels of wheat into flour annually. Millers have increased their purchasing of southeastern wheat due to the improved quality of new cultivars. Millers purchase wheat with a protein content of 11 percent or less and a test weight of 58 lb/bu or above. The quality of wheat grown in the Southeast is dramatically influenced by the season and cultivar. Variation for quality traits can exist within a state due to soil type, agronomic management and cultivar selection. Diseases of wheat also affect milling and baking quality of soft red wheat. In one test, the most susceptible variety to powdery mildew had the lowest protein content and the best quality when disease levels were high. However, reductions in wheat quality often occur in response to severe leaf rust infection. Protein content often increases as disease severity increases.

Time and rate of nitrogen (N) fertilization influences milling and baking quality. Fall N application above 30 lb/A has a detrimental effect on quality traits. Spring N rates reduced baking quality by increasing protein content. The trend toward rates above 80 lb/A may result in higher protein content, which would lower baking quality. Nitrogen applications at the recommended rate of 60 to 80 lb/A in the spring do not result in any adverse effects on milling and baking quality.

In summary, cultivar selection can play an important role in milling and baking quality. Wheat diseases in the Southeast can influence quality if they reduce test weight. The recommended N rates of 60 to 80 lb/N in the spring should not alter milling and baking quality.

Know All Your Costs

Outlays for fertilizer, seed and fuel are usually considered major cost items for growing wheat. But there are numerous small cash outlays plus allowances for items such as equipment depreciation, farm overhead, management and profit. It is essential to know all these costs for any enterprise analysis.

The first step in wheat production is to estimate the costs per acre, and then get these costs on a per bushel basis. The worksheet in Table 28 is designed for this purpose. Costs estimates are given for two systems of wheat production 1) one that includes those inputs necessary to obtain an average wheat yield of 40 bu/A, and 2) a system of intensive management to achieve a yield of 75 bu/A. These latter input levels will not ensure higher production levels but are a prerequisite to a more intensive management system to attempt those yield levels.

The production costs are not precise. They are intended to provide guidelines to help each producer estimate his own costs for the production system being considered. Several cost items included in the worksheet are non-cash items — machinery depreciation, management, family labor and land costs (if the land is owned). A wheat grower can usually cover cash costs with wheat sales. But these non-cash items are included to point out the sale price needed to cover all costs over a period of time.

Table 28. Wheat for grain cost worksheet