The University of Georgia College of Agricultural & Environmental Sciences
Cooperative Extension Service

Intensive Wheat Management in Georgia

R. Dewey Lee, Extension Agronomist

Table of Contents

WHEAT GROWTH STAGES
VARIETY SELECTION
PLANTING DECISIONS
FERTILITY MANAGEMENT
INSECT MANAGEMENT
DISEASE MANAGEMENT
WEED MANAGEMENT
LIQUID NITROGEN TANK-MIXES
PLANT GROWTH REGULATORS
DOLLARS AND CENTS OF HIGH YIELD, INTENSIVE WHEAT PRODUCTION
HARVEST MANAGEMENT

New techniques developed in the southeast United States over the last decade in soft red winter wheat production have increased yields on farms considerably. Research started in the early 1980s shows that yields of soft red winter wheat can reach over 100 bushels per acre with the right environment.

Wheat growers who have used and adapted the principles discussed in this publication have increased their yields and improved their profits. More and more producers are successfully using intensive, high yield management techniques which are reflected in production increase per acre in the state over the last several years (Figure 1). Although average yields in Georgia are in the low 40 bu/A, some farms using intensive management techniques have averages over 65 bu/A.

Figure 1. Wheat Yields in Georgia Crops (2-year average) 1983-1994.

This publication includes the basic guidelines for high-yield, efficient wheat production. Factors such as soils, crop rotations, climate, field-to-field variation and equipment make it necessary for all producers to make some site-specific adjustments to achieve the highest yield potential.

Growers who have been the most successful in the transition from conventional to intensive wheat management have (1) started with a small acreage, (2) utilized all the basic principles and adjusted according to their conditions, (3) adopted the most successful practices, (4) concentrated on timeliness, and (5) marketed a quality product, therefore obtaining the highest possible return.

Study the following guidelines to see what areas you can improve on your farm.

Wheat Growth Stages

The timing and correct applications of nitrogen and pesticides depend upon understanding and recognizing various growth development stages for successful intensive, high yield wheat production.

A brief outline and description of the various wheat growth stages are in Table 1. Numbered growth stages identify the development or formation of specific plant parts. The two scales most frequently used are the Feeke's and Zadoks' scales. The Feeke's scale is a numerical system for describing wheat growth, but is not very specific during some stages. The Zadoks' scale is based on a two-digit descriptive system which gives more details on development. Growth stages should be used as an aid for proper timing of applications such as nitrogen and pesticide. The best way to learn the stages is to observe the crop growing and carefully determine the proper growth period as it happens by comparing the crop with the aids given in this bulletin.

Germination and Seedling Growth

Wheat seeds germinate at temperatures between 39 degrees and 99 degrees F. Optimum germination is between 68-77 degrees F. Germination is indicated by the primary root protruding through the seed coat followed by the emergence of the coleoptile (first leaf). Germination is complete within four to six days at optimum temperatures. Seedling roots begin to grow as the coleoptile emerges. Seedling growth begins with the emergence of the first leaf above ground and continues until tillering. Generally the wheat plant develops three or more leaves before tillering. The fibrous root system of the seedling usually develops faster than the above-ground vegetative portion and helps support a vigorous healthy plant.

Figure 2. Wheat plants at Seedling State, Feekes' GS 1.	Figure 3. Wheat plants at Full Tiller, Feekes' GS 4.

Tillering

Tillering is the development of shoots from buds at the base of the main stem. During development, tillers depend upon the main stem for nutrition. Once three or more leaves develop, tillers become independent of the main stem for nutrition and form their own roots.

Tillers have the potential to develop grain-bearing heads that are the major component to yield. Secondary tillers may arise from the primary tillers. Tillering increases with light intensity, low plant populations and high soil nitrogen availability and usually declines with high temperatures, high plant populations, soil moisture stress and pest.

Vernalization

Usually the onset of reproduction is controlled by vernalization. This process begins through the extended exposure of the growing point to low temperatures. This process has been shown to begin in seeds as soon as they absorb water and swell. Adapted varieties in Georgia generally require two to six weeks of vernalization. The effectiveness of vernalization declines with increasing plant age. Once vernalization requirements are met, the growing point differentiates. This means that all leaves have been formed and the growing points, which generate new cells for the plant, will begin to develop an embryonic head. At this stage of growth, the size of heads or number of flowers per head is determined. No effect on yield is expected from tillers developed after this stage. Nitrogen applied after this stage can affect the number of seed per head and seed size, but will not likely affect the number of heads harvested.

Vernalization is affected by photoperiod. In some varieties, exposure of the wheat plant to short days replaces the requirement for low temperatures. In some cases, if wheat is exposed to high temperatures (86 degrees F>) shortly following low temperatures, vernalization is interrupted.

Following vernalization, the initiation of head development will be hastened by longer photoperiods. Generally early-maturing varieties require fewer days of chilling hours or vernalization than later-maturing varieties.

Stem Elongation and Jointing

Stem elongation occurs just at the beginning of the reproductive stage. The embryonic heads that have formed at the base of the plant begin to "move up" the stem. The maximum possible numbers of seed per head is formed at this time. Jointing begins when the first internode of the stem is visible. Generally wheat stems will possess several internodes increasing in length from the base of the plant to the top. Prior to this stage, the nodes are all formed but are so close together that they are not readily distinguishable to the naked eye. As jointing begins, the first node is swollen and appears above the soil surface. Above this node is the head which is being pushed upwards to eventually emerge from the boot. The head at this stage is completely differentiated containing all potential flowers. At this stage, do not apply phenoxy herbicides such as 2,4-D or MCPA, since these materials can be translocated into the developing head causing distortion or sterility.

Another important growth stage in stem elongation is the appearance of the last leaf, the flag leaf. The flag leaf produces a large proportion of the carbohydrates for grainfill. It must be protected if necessary from disease and insects in order for the plant to develop its yield potential. The boot stage occurs shortly after flag leaf emergence and indicates that the head is about to emerge. Reproductive development is first observed when the head begins to swell within the flag leaf sheath. The boot stage ends when the wheat head first emerges from the flag leaf sheath.

Figure 4. Wheat plant at Jointing Stage, Feekes' GS 7. Notice hollow internodes between nodes.

Heading Stage

The heading stage is first observed when the head emerges from the flag leaf sheath.

Small grains are normally self-pollinated. When the head or inflorescence has emerged, pollination (anthesis) occurs. Seeds per heads are determined by the number of flowers 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.

Frost may result in head injury and partial or complete sterility. Usually short season or early maturing varieties are more susceptible to frost injury due to the earlier head emergence than seen in full-season wheat.

Figure 5. Wheat plants at Flowering Stage, Feekes' GS 10.51.

Grain Filling

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

Grain Maturity

Wheat is physiologically mature in the hard dough stage. The moisture content may range from 25 to 35 percent. Harvest can begin once the wheat grain has reached a suitable moisture level. It is important for grain quality that the harvest begin as soon as possible.

Variety Selection

Variety selection may be the most important management decision made in efficient high-yield wheat management. Without good genetics, the chances of reaching high yields of wheat are very limited. Yield is obviously the first characteristic in variety choice. While most varieties may yield similarly in low-yield environments, not all varieties have equal yield in high yield environments. It is important therefore, to use all the available information on varieties adapted to your area. Consider all information that comes from company trials, University Experiment Station variety trials and county demonstration trials. The University of Georgia annually publishes the Small Grain Performance Test bulletin. This report is usually available at local county extension offices.

Performance data should include disease resistance, insect resistance, heading dates, lodging rates, height, test weight and yield. No variety is perfect for all environments. Therefore, use several varieties on your farm to reduce the risk of the total crop being susceptible to losses from some unseen problem.

Varieties should be adapted to the production scheme and to the area where they are to be grown. For example, if plans are for doublecropping, use early maturing varieties. There is some risk in exposure to late spring frost when early-maturing varieties are planted early in the recommended planting period. Consider planting later in the recommended plant period to avoid excessive growth or very early heading. Match the right maturity group to your operation. Late-maturing varieties take the greatest amount of time to mature and often have the longest cold requirement for vernalization. Therefore they need to be planted as early as possible to avoid problems with vernalization and to increase disease pressure.

Pest resistance is the first and least expensive line of defense against diseases and insects. No variety is completely immune to disease or insects. But great differences occur between varieties. Yearly re-evaluation of variety choice is necessary to ensure that the shift of disease populations have not effectively eliminated or reduced the usefulness of the genetic resistance of varieties used on your farm.

Varieties vary in straw strength and height. Select varieties with good straw strength to prevent harvest losses associated with lodging. High yield wheat management utilizes higher rates of nitrogen than conventional management. Varieties with poor straw strength typically will lodge when grown under heavy nitrogen applications. Only use varieties with good lodging resistance in high yield management schemes.

Test weight is another characteristic that must not be overlooked. Standard test weight for US #2 wheat is 58 lbs/bushel. Test weight below the standard usually results in a price dockage at the elevator. Therefore, select the variety that has the best combination of all the characteristics needed in the high yield environment.

Once the varieties have been selected, certified seed is the best guarantee of obtaining the necessary qualities of good seed such as good germinations and freedom from weed seeds. Research shows in comparison with bin run seed, certified seed out-performs bin run seed. The extra profit from certified seed more than compensates for the higher cost in seed prices.

Valuable information can be obtained through studying The Small Grain's Performance Test Bulletin. Follow the guidelines listed below to correctly use the data.

How to Use Performance Test Reports

• Select the test location that best represents your production area and soils.
• Use multiple year averages since they are the best predictors of performance over several environments.
• Select current varieties you are familiar with and use them to compare other varieties.
• Identify those varieties which out-yield your current varieties.
• If the yield difference between varieties is greater than the LSD (least significant difference) 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. The LSD value is usually located at the end of the table.
• Check the other columns for other characteristics. Avoid varieties with low test weight, high lodging potential, and poor pest resistance.
• Your soils and management may differ from those of the test location. Therefore, use several different varieties in your own on-farm test program to determine the best variety to expand in your high yield wheat production.

Planting Decisions

While variety selection is important, other planting decisions have great impact on yield. These planting decisions include seed bed preparation, planting date, planting method, seeding rate, seeding depth and row width. The objective is to obtain the appropriate population of a uniformly- emerging wheat crop planted on time for your particularly area. It is estimated that the majority of the yield potential for a specific season is determined as soon as planting is finished. Improper variety selection, poor seed quality, late planting and improper plant population usually cannot be overcome with management practices later in the season. Timeliness and precision therefore are key factors in obtaining the best yield.

Planting Date

Planting date is a critical component of successful wheat production. Planting too early or too late usually reduces yield potential.

Plant within the recommended planting date for your area in order to obtain the highest yields possible. Acceptable yields of wheat can be obtained when planted later than the recommended period, but yield potential is reduced when compared to plantings made during the recommended period. Planting during the recommended period provides adequate time for tilling and root development and reduces the potential for yield loss.

Planting wheat earlier than the recommended period will subject it to greater insect and disease pressure and subsequently to more winter injury. Although wheat emerges sooner and the shoot (above ground portion) develops faster in warm soil (75-80 degrees F), the root system develops much faster and more extensively if the soil is cool (55-60 degrees F).

Planting later than the recommended date may be even more damaging to yield potential. Late-planted wheat will have fewer tillers and thus fewer heads thereby reducing the yield potential. Georgia's Crop Reporting Service estimates show that 35 percent of Georgia's wheat crop is planted each year after the recommended planting period.

If certain late-maturing wheat varieties are planted extremely late, the vernalization requirement may not be satisfied and the plant may not produce grain heads.

If planting is delayed near the later portion of the recommended periods or slightly beyond, use an early maturing, short-vernalizing variety. Figures 6and 7 illustrate the effects of planting dates on wheat varieties in Georgia.

Figure 6. Effects of planting date on Soft Red Winter Wheat in North Georgia.

Figure 7. Effects of planting date on yield of Soft Red Winter Wheat in South Georgia.

The optimum planting date for wheat depends upon where the crop is grown. Table 2 shows the suggested planted periods for grain production in the four major production regions of Georgia.

Seed Bed Preparation and Crop Rotation

Wheat performs best when planted on well-drained, fertile soils that have been prepared as a smooth, firm and weed-free seedbed. Incorporating old crop residue in the soil reduces seedling diseases and insect losses. Deep tillage increases yields especially on Coastal Plain and Piedmont soils which tend to compact.

Yield increases of 3 to 8 bushels per acre have been observed when some form of deep tillage has been utilized. Deeper tillage allows for easier root penetration, burial of disease debris, dilution of root pathogens and improved water infiltration and soil aeration. In wet years, low soil oxygen conditions are enhanced by compacted, dense soils. This condition results in yield loss due to the detrimental effects on root production and nutrient uptake.

Wheat yields are improved through crop rotation. Wheat should not be grown on the same land two years in succession because of the increase in pest problems. Disease, insect and weed problems are usually reduced with crop rotation. Studies show that rotating with oats reduces some disease problems found in wheat. Wheat also fits well into rotations with many summer crops.

Figure 8. Well-prepared seedbed necessary for establishing a good stand.

Planting Methods and Seeding Depth

A grain drill is the best tool for planting wheat. In comparison to broadcasting, planting with a drill reduces seed costs, ensures better emergence because of seed placement and produces more uniform stands. A 10 to 15 percent yield increase for drilled vs. broadcast wheat is common.

Seed placement will influence the uniformity of emergence, final stand and the yield potential of the corp. Under optimum planting conditions, you can plant wheat 1 to 1 1/2 inches deep and expect to produce a good stand. Planting deeper than 2 inches may delay emergence. Planting seeds shallower than 1/2 inch may result in uneven germination and emergence due to the drying of soil. Using a drill with depth-bands is the most effective method of positive seed depth control.

If wheat is planted deeper than 3 inches, a large portion of seedlings may fail to emerge and be abnormal once they do emerge (Table 3). This is because many seed lack the food reserves necessary to emerge from deep in the soil.

Seeding Rates

Wheat seed size varies greatly from year-to-year among varieties and between seed lots of varieties. Wheat seed may range from 12,000 - 18,000/lb; therefore seeding based on seeds/area is much more accurate than seeding based on weight/area. Planting rates in terms of bushels/A or lbs/A without consideration of the seed size can produce stands which have either too high or too low populations. The differences in number of seed/lb exists because seed weight or kernel plumpness is determined primarily by the environment in which it is grown and by the degree of cleaning. For this reason, it is important to plant on a seed/row-foot basis. Tables 4 and 5 can be used as a guide to calibrate your drain drill for optimum seeding rate. Research and experience show that 35 to 38 seeds/sq. ft is needed for maximum yields. Seeding rate should be increased 10 percent for each week delayed in planting after the optimum planting date.

Table 6 shows the seeding rates for wheat based on seed size and illustrates the differences in pounds/A.

Utilize the following step-by-step procedure to calibrate your drill.

Step 1: Select the proper seeding rate/row foot for your drill width from the tables. These figures are based on a seed germination test of 90%. For seed that has less than 90% germination increase the rate in proportion to the percent germination that is less than 90%.

Step 2: Calculate the number of seeds required in 50 feet of row. For example, in 7.5 inch wide rows and planting on time, an appropriate seeding rate would be 22 seeds per drill-row foot times 50 feet, which equals 1100 seeds planted every 50 feet of each row. Count 1100 seeds of each variety and put the seed in a graduated tube such as a rain gauge, or a clean tube or cup. Mark the level of the 1100 seeds in the tube.

Step 3: Hook a tractor to the grain drill so that the drive wheels of the drill can be raised off the ground with a jack, and the drive gears can be engaged. Raise the drive wheel so it clears the ground and turn the wheel several revolutions to be certain that everything is turning freely. Check all drill spouts and make sure there are no blockages.

Step 4: Determine the number of revolutions the drive wheel must turn to travel 50 feet. This can be done in one of two ways.

Option a. Measure the distance around the drive wheel. The distance can be measured directly with a tape measure or calculated by measuring the total distance across the tire and multiplying that distance by a factor of 3.2. For example, if the drive wheel measures 30 inches from tread to tread, then the distance around the tire should measure 96 inches (30-inches X 3.2). The number of tire revolutions per 50 feet is calculated by the following formula:

Inches traveled in 50 feet = 50 feet X 12 inches/foot= 600 inches.

Number of tire revolutions per 50 feet = 600 inches divided by 96 inches per revolution = 6.25 revolutions of the tire per 50 feet of travel.

Option b. Measure 50 feet in a field and count the number of revolutions the drive wheel makes in 50 feet. (Always check the number of tire revolutions per 50 feet on soil conditions similar to those that will be experienced during planting. This is especially important if the drive wheel is small and slippage is a problem).

Step 5: To calibrate the drill:

a - Raise the drive wheel off the ground so it can be easily turned.
b - Put at least a quart of seed of the lot to be calibrated over each of two adjacent drill spouts.
c - Turn the drive wheel several revolutions so that seed is flowing through the drill and stop the wheel at a convenient mark such as the valve stem straight up or mark on the tire.
d - Remove the rubber boot from the two drill spouts with seed and place a container under each spout to catch the seed. Catch the seed from each spout in a separate container.
e - Adjust the seeding rate to a setting that is expected to be close and turn the drive wheel the appropriate number of turns for traveling a distance of 50 feet (determined in Step 4).
f - Pour the seed from one row into the pre-calibrated tube from Step 2. Check the second row the same way.
g - If the seeding rate is too high or too low, change the drill setting and repeat steps e and f in this list until the appropriate seed number is obtained.
h - Steps d-g should be repeated on two rows on the opposite side of the drill if the drill is driven by more than one drive wheel.
i - Remove seed from the drill and put in the next variety, or seed lot, to be calibrated. Repeat the procedure.

Row Width

Most drills in Georgia have 6-to-8 inch row widths. While farm yields of over 100 bushels/A have been achieved with 6 to 8-inch row spacings, row widths of 4 inches have been shown in research to produce 5 to 10 per cent more grain than wheat planted in 7-inch rows. Wheat should be planted with as narrow row-width as possible. It is essential that wheat be planted at a uniform depth. Four-inch row drills may be desirable but also may be impractical in Georgia's conditions. Four-inch row drills can be clogged with excessive surface residue or dirt clods. Conventional drills can be used successfully in producing high yield wheat.

Tramlines

Tramlines are traffic lanes formed by closing one or two drill openings when planting. Tramlines may also be formed after the wheat has emerged by chemically killing the rows that match the width of the tractor tires or implement used to apply fertilizer and spray pesticides.

Tramlines are used extensively in Europe where applications of chemicals and fertilizers are repeatedly made. Although this practice has not been used in Georgia that much, it seems appropriate when more than three trips across the field will be made in the spring. Tramlines make uniform applications of nutrients and pesticides much easier. There are several advantages to using tramlines.

1. They improve the precision of applications of nutrients and of pesticides.
2. They act as guides for repeated applications of materials.
3. They become compacted strips for driving when soil is wet.
4. They offer less chance for disease development than when plants are crushed because of running over standing wheat.
5. Border plants along the strips will compensate for yield losses whereas plant damaged by tires rarely produce grain.

Figures 9 and 10 illustrate a tramline system that matches the drill passes and spray boom width. Tramline installation in the farming system is relatively simple. Devices for drills can be purchased and are available to establish tramlines on any track width in any multiple of drill widths. Contact your equipment dealer or county Extension agent for location of such devices. The wider the tramlines are, the less damage takes place in the crop.

Figure 9. Preparing and using a tramline system. (a) Seeder has drill opening closed to make tramline; (b) Seeder has drill opening in open position to seed crop. Tramlines are now at specific width for spray boom to cover whole field exactly. (c) Tractor using tramline to spray.

Figure 10. Sprayer using a tramline in a wheat field.

Fertility Management

Nitrogen Management

Nitrogen management is a key factor in high-yield wheat management. Nitrogen fertilizer is the most expensive variable cost in wheat production. It is critical that this input be managed for maximum return on this investment.

Nitrogen comes in liquid and dry sources. Research shows that most sources of nitrogen are acceptable in high yield wheat production systems. While ammonium and ammonium forming fertilizers (such as urea and UAN solutions) may lose significant amounts of nitrogen due to volatilization, the loss is not considered to be as large in wheat production because temperatures in late fall to early spring are low and losses are likely to be small.

Nitrogen rates will vary depending on yield goal, soil types, cultivar, soil moisture, previous crop and residual N. As nitrogen rates increase, the potential for lodging, disease, winterkill and groundwater contamination increases. Excessive nitrogen will also reduce milling and baking quality. On the other hand, inadequate nitrogen will limit yield potential.

The key is to provide the essential amount of nitrogen at critical growth stages for most efficient use. Nitrogen fertilizer rate and timing are the major tools available to manipulate wheat to produce higher yields per acre. Nitrogen affects yield by influencing the yield components: heads per acre, grains per head and grain weights.

In Georgia research, wheat which has yielded at least 100 bushels per acre contained about 120 lbs N per acre in the grain, 30 lbs N per acre in the straw and about 30 to 50 lbs N per acre in the roots for a total of 180 to 200 lbs N per acre. Some of this nitrogen comes from residual soil nitrate, from mineralization of soil N but mostly from fertilizer - N. For expected yields of 40 to 70 bushels per acre, use a total of 80 to 100 lbs N/Acre. Results from Georgia and Alabama indicate that for most soils, applications of 120 lbs N per acre is necessary for yield goals of 70 to 100 bushels/A. However, on sandy soils with high yield potential more nitrogen may be necessary to maximize yields.

Nitrogen should be available in the fall to stimulate growth and increase tillering. Excessive fall nitrogen subjects nitrogen to potential leaching rainfall and the crop to winter injury. For high yields it is desirable to obtain 50 to 70 heads per square foot. To achieve this, there has to be enough nitrogen for wheat to develop 80 to 100 tillers per square foot prior to stem elongation. It is therefore important to apply nitrogen in the fall as preplant or soon after emergence.

On sandy soils where residual soil nitrogen is usually low, applications of 30 to 40 lbs in the fall are necessary to obtain adequate tillering N or high yield wheat. If wheat follows a legume such as peanuts or soybeans, the nitrogen application in the fall may be reduced to 20 lbs per acre.

On heavier-textured soils such as clay loams, residual soil nitrogen is usually higher. Nitrogen rates may be reduced to 20 lbs per acre. When following a legume, no nitrogen is necessary since mineralization of organic matter supplies adequate nitrogen for tillering.

The remaining nitrogen should be applied prior to stem elongation and jointing. Research in some states indicates that nitrogen can be applied in late winter to stimulate tillering if tillering is inadequate for higher yields. In sandy soils, topdressing applications at early tillering and early jointing improve yields when leaching conditions occur or where more tiller growth is desired.

The timing of nitrogen is critical to obtain large numbers of well-filled heads. Base nitrogen timing on the crop's nitrogen uptake pattern. During the fall, plant growth is limited and nitrogen uptake is minimal. Only a small amount of nitrogen is required to establish a healthy plant. During winter dormancy wheat utilizes only a small amount of nitrogen (Figure 11).

Figure 11. Nitrogen uptake pattern for Soft Red Winter Wheat in Georgia.

An important period for nitrogen management is just prior to stem elongation and jointing. During this time, the potential number of grain per head is being determined. Sufficient nitrogen must be available to avoid limiting the number of grains. Inadequate N will also result in the abortion of tillers. The reduction in tillers will mean fewer heads per acre. Thus inadequate nitrogen at this stage can cause major yield losses by reducing the number of heads per acre and the number of grains per head.

Rapid nitrogen uptake begins to occur when stem elongation and jointing begin. Figure 11 illustrates this demand. Since the nitrogen demand is high and uptake is rapid at this state, it is critical to apply most of the spring nitrogen prior to this stage. Nitrogen topdressing applied too early is subject to leaching, runoff losses and denitrification. In addition, nitrogen applied too early can stimulate excessive growth which may result in winterkill and lodging.

Split applications of nitrogen in the spring in some cases result in higher wheat yields. The benefits of split spring applications are most likely to occur on sandy soils or in situations where excessive nitrogen losses have taken place through leaching or denitrification.

Nitrogen applications can be aided by establishing tramlines in the field. Although split applications of nitrogen are not always beneficial, tramlines will aid in uniformity, precision and timeliness of applications.

Research in some states shows that nitrogen rates may be reduced based on tiller number, chlorophyll meter readings, tissue N concentration and soil nitrate level. While these methods have not been fully refined in Georgia, they warrant consideration. An excellent publication detailing some of these methods is Intensive Soft Red Winter Wheat Production, Virginia Polytechnic Institute and State University Publication. 428-803. Some of these techniques are being researched in Georgia to determine how beneficial they might be to Georgia producers.

Phosphorus and Potassium Management

Proper fertilization with phosphorus and potassium is essential for the production of high-yield wheat. A soil test is the most accurate method to determine phosphorus and potassium needs. Soil testing assesses the nutrient supplying power of the soil. Once this is evaluated, the amounts of supplemental fertilizer required can be determined and applied. Always base phosphorus and potassium fertilization on soil test results. Table 7 shows the amount of nutrients removed by 50, 75, and 100 bu/A wheat. All nutrients should be at least in the high range when trying to produce top wheat yields.

Since 65 percent of the total phosphorus uptake and 90 percent of the total potassium uptake occurs before the boot stage, these nutrients should be applied accordingly before planting and thoroughly incorporated into the root zone. Potassium is more mobile than phosphorus in soil and can be leached below the root zone of wheat. For this reason, on deep sands (soils with greater than 12 inches above the clay layer) it is suggested that one-half of the potassium fertilizer be applied in the fall and add the remainder in the spring. A single fall application is acceptable on all other soils.

Secondary Nutrients

The essential secondary nutrients required for wheat production are calcium, magnesium and sulfur. Calcium and magnesium are normally supplied by dolomitic limestone. Maintaining soil pH near 6.0 or better will normally ensure that the calcium and magnesium soil levels are sufficient. There are some instances where the soil pH is greater than 6.0 and the magnesium soil test levels are low. The most common cases where this occurs is when calcitic limestone is utilized. In this situation, supplemental magnesium fertilizer is recommended, but limestone should not be used.

Sulfur is a very mobile nutrient in many Georgia soils. Because it is most frequently present in the sulfate form, it can be readily leached in the deep sands found in the Coastal Plains. Sulfur is generally recommended when the depth to the clay is greater than 14-16". The application of at least 10 lbs/A of sulfur applied at top-dressing time in the spring is recommended for wheat planted on deep sands. If a sulfur deficiency is suspected, determine the tissue content and if the nitrogen-sulfur ratio is greater than 15:1, apply the recommended amounts of sulfur as soon as possible.

Micronutrients

Micronutrient levels in Georgia soils are adequate for wheat production unless the soils are over-limed. Low zinc levels may occur in the soils of the Coastal Plain. A soil test readily detects this condition and it is easily corrected by applications of 3 lbs of elemental zinc/A in the pre-plant fertilizer. Manganese deficiency occurs most frequently in poorly-drained soils in the Flatwoods Region. Availability of manganese declines significantly as pH increases above 6.2 to 6.5 in these soils. Soil applications seldom correct the problems since manganese is readily converted to unavailable forms. Foliar applications of 0.5 lbs of manganese/A as manganese sulfate or .25 lbs of manganese/A as manganese chelate will correct deficiencies. But two or more applications may be required.

Insect Management and Control

Wheat is infested by a host of different insect pests that can at times cause significant injury. Estimated losses to insects in Georgia annually runs into the millions of dollars. Historically, the Hessian fly and aphids are our primary pests of importance. Recently, we have seen secondary pests such as armyworm and chinch bug gain in importance. Incidences of barley yellow dwarf, a viral infection transmitted by aphids, have also increased. Regardless of the pest, it is important that growers be aware that insects can significantly limit their profit potential by reducing yields. Listed below are the primary insect pests of wheat and the suggested scouting procedures and control methods for each.

Primary Insect Pest Biology and Damage

Hessian Fly

The Hessian fly, Mayetiola destructor, is a major factor limiting wheat production throughout the southern United States. Wheat is the primary host of the Hessian fly, but the insect also will infest triticale, barley and rye. Hessian fly does not attack oats. Little barley is the only other important host in Georgia.

Adult Hessian flies are small black flies about the size of a mosquito. Adults live about two days during which they mate. Females lay about 200 eggs in the grooves of the upper side of the wheat leaves. Eggs are orange-red, 1/32 inch long and hatch in three to five days. Young reddish larvae move along a leaf groove to the leaf sheath and then move between the leaf sheath and stem where they begin to feed on the stem above the leaf base. Maggots become white after molting and appear greenish white when full grown. Maggots molt into a resting (puparial) stage which is often referred to as the 'flaxseed' stage because the pupae resemble seeds of flax. The entire life cycle requires about 35 days at 70 degrees F. Newly-hatched larvae are prone to drying while they are exposed on the leaf surface, but once larvae move to the stem base, they are protected from weather extremes.

Figure 12. Hessian Fly adult.	Figure 13. Hessian Fly pupae on wheat stem.

Maggots suck sap and stunt tillers presumably by injecting a toxin into the plant. Feeding by a single larva for several days is sufficient to completely stunt the growth of a vegetative tiller. Stunted vegetative tillers are dark green, do not elongate or produce new leaves and usually die after the maggots pupate. Infested-jointed stems are short and the stem is weakened at the joint where feeding occurs. Grain filling of infested stems is reduced and damaged stems often lodge before harvest. Although not clearly defined, yield losses usually occur when stem infestation exceeds 20 percent.

The Hessian fly is a cool season insect and is dormant over the summer as a puparia (flaxseed) in wheat stubble. The number of generations during the year is governed largely by temperature. Generally, three to four generations occur in the Piedmont region of Georgia and four to five generations occur in the Coastal Plain with a sixth generation being possible in the lower Coastal Plain. Adults emerge from oversummered flaxseed in wheat stubble about September 1. Since wheat is not yet planted, the first generation develops entirely in volunteer small grains and weed hosts. A second and sometimes third generation occurs in late fall and winter. In the spring, one generation occurs in the Piedmont region, whereas one or two generations occur in the Coastal Plain. The fall and winter generations stunt and kill seedling plants and vegetative tillers. The spring generation infests jointed stems during or after head emergence. Not all flies, however, emerge the following generation. A small proportion of each generation (about 5 percent) will remain dormant and emerge at a later time; consequently, an emergence of flies may represent the offspring of several previous generations.

The use of resistant plant varieties has resulted in the development of numerous Hessian fly biotypes. Biotypes are identical to each other and to the parental type, except that each biotype has the ability to overcome a specific set of wheat genes for resistance to the pest.

Aphids

Aphids are small soft-bodied insects found in wheat anytime during the growing season. For the most part, aphids are controlled by beneficial insects like lady beetle. But, for the last two seasons insecticide controls have been needed. Several aphids infest small grains. The most common aphids found in Georgia on wheat are oat bird cherry aphid, corn leaf aphid, greenbug and English grain aphid. The first three species occur mostly in the fall and winter. Only the greenbug causes direct feeding damage that appears brown and discolored. The other aphids do not cause direct feeding damage. The English grain aphid is mostly present in the spring and can reach large numbers on flag leaves and developing grain head. Treat when 25 or more of these aphids are found on developing grain heads. Treatment is not needed during hard dough and later stages.

Aphids are mostly a concern in small grains because they vector a viral disease, barley yellow dwarf virus (BYD). Oats are most susceptible to this disease but wheat and barley also are severely damaged. Yield loss is greatest when plants are infected as seedlings in the fall. Yield of infected wheat plants usually is reduced by 50 percent. Georgia has had two years of increasing damage from this disease. A survey conducted in 1994 indicated the presence of barley yellow dwarf in every field surveyed in south and central Georgia. Epidemics of this disease can significantly reduce yields, but most Georgia wheat fields never reached epidemic levels. Early plantings generally have greater aphid numbers and therefore greater barley yellow dwarf incidence than late plantings.

At this time, we do not have sufficient data to support a season long strategy of foliar insecticide sprays to suppress aphids and the incidence of barley yellow dwarf. A new insecticide seed treatment, Gaucho, is very effective at controlling aphids and can substantially reduce BYD infections. An at-planting application of a granular systemic insecticide (Di-Syston, Thimet or Phorate) also will reduce aphid numbers in the fall, but this treatment is variable and inconsistent in reducing BYD infections.

Figure 14. Aphid colony on wheat leaf.		Figure 15. Barley Yellow Dwarf Disease in wheat.

True Armyworms

The true armyworm looks much like other armyworm species. It is brown to black in color. Larvae have three, orange, white and brown stripes running the length of each side. The larvae will also have a narrow broken stripe down the center of its back. One interesting characteristic that can sometimes be used to separate it from other armyworms is the presence of black spots located at the top of the four pairs of prolegs.

The damage the larvae causes in wheat is fairly evident. Severe infestation will leave only a stalk standing in the field. Since the worms hide during the day at the base of the plants under the plant residue, they are somewhat hard to find. They feed late in the afternoon and at night on leaf tissue. They often will cut off about as much foliage as they eat. It is reported that heavy populations will cut heads of barley. Cut wheat heads have not been observed in Georgia. They will also feed on the tips of the developing wheat seeds causing lower yields and lighter test weights.

Wheat fields should be checked for the presence of true armyworms. If two to three worms per foot of row are found, consider treatment. Several materials are labeled that give excellent control in wheat.

Figure 16. Armyworms in wheat.

Cereal Leaf Beetle

Cereal leaf beetle, Oulema melanopa, is a new wheat pest and was first discovered in 1989 in Georgia. The insect occurs throughout the mountain and piedmont regions and was found in several counties in the upper coastal plain in 1995. Currently, populations have increased to damaging levels only in the northwestern region of the state. Cereal leaf beetle feeds on many grasses including oats, wheat, barley, rye, orchardgrass and annual ryegrass but is a problem mostly on oats and wheat.

Adult beetles are 5 mm long, and blue-black with a reddish thorax (neck) and legs. Larvae are yellow-white and up to 6 mm long, but appear shiny black because they are covered with fecal material. Adults and larvae defoliate or skeletonized long narrow sections of the flag and upper leaves. There is one generation per year; adults oversummer and overwinter in fence rows and wooded areas. Adults are present in wheat during March and April when they mate and lay eggs. Larvae are present in April and May during head emergence through the dough stage of wheat development. Damage grain yield and test weight mostly by reducing seed size.

Wheat can tolerate considerable defoliation. Yield losses usually do not occur until flag leaf defoliation exceeds 50 percent. Cereal leaf beetle can be effectively controlled by one application of an insecticide to foliage. Fields should be scouted by counting the number of larvae and adults on 10 stalks at 6 to 10 locations per field. Consider treatment when populations exceed 1 larvae and/or adult per stalk after seed head emergence and 0.5 per stalk before seed head emergence. Treatment should be made after most eggs have hatched but before larval damage becomes extensive.

Management Tactics

Varietal Selection

The most efficient and economical method for controlling the Hessian fly is the use of resistant varieties. Information on varietal selection and Hessian fly resistance is provided by the annual Small Grain Performance Tests bulletin and is also listed in the annual Wheat Production Guide published by the Cooperative Extension Service Crop and Soil Science Department. Wheat varieties grown in the Southeast do not contain high levels of resistance to any other insect pests.

Cultural Practices

Several cultural practices can aid in the management of insect pests in wheat. Most insect pests, including the Hessian fly, aphids, 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 that include moldboard plowing. Table 8 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. Moldboard plowing buries wheat stubble where Hessian flies over-summer and suppresses volunteer wheat in the late summer. No tillage also may enhance fall populations of aphids which are attracted to the plant stubble.

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 any 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 9. 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 where activity can occur throughout the winter. Spring populations are not affected by planting date. Wheat planted early for grazing by livestock is particularly vulnerable to attack by insects especially the Hessian fly. Therefore, either rye or a Hessian fly resistant wheat should be planted for grazing.

Burning stubble in the spring and fall grazing may reduce insect populations some, 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, but insects are highly mobile; consequently, crop rotation may not be as effective as it is for less mobile wheat pests.

Insecticides

Insecticides generally are not widely used in wheat in the Southeast. Except for the Hessian fly, all other insect pests can be controlled by applying foliar insecticides when population densities exceed economic thresholds (Table 10). Consult the Georgia Pest Control Handbook for specific chemical recommendations.

Use of granular insecticides applied at planting for Hessian fly control is highly recommended on susceptible varieties. Di-Syston^R Thimet^R and phorate applied at 1.0 pound active ingredient/acre at planting are effective in controlling Hessian fly for about 45 days. These insecticides, however, must be applied in-furrow. 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. Therefore, a treated field may be heavily damaged after the insecticides become ineffective. Studies in Georgia indicate that foliar applications of insecticides in the spring for Hessian fly control are highly variable in effectiveness and are not currently recommended. A new insecticide seed treatment, Gaucho^R was registered for use on wheat in late 1995. Gaucho^R is very effective in controlling aphids in the fall and winter and can reduced infection rates of barley yellow dwarf virus by 75 percent. However, Gaucho ^R will be expensive ($9.00-12.00/acre). At current wheat prices ($3-$4.00/bu), a 3-4 bu/acre yield response is needed to break even. Consequently, Gaucho^R should be considered as a seed treatment when (1) grain yield potential is high (>60 bu/acre), (2) a field has a history of BYD infection, and/or (3) early plantings.

Summary of Management Practices for Hessian Fly

1. If possible, avoid continuous planting of wheat in the same field.
2. Select a Hessian fly resistant variety adapted to your area.
3. Control volunteer wheat.
4. Plow fields to bury wheat debris.
5. Do not plant wheat for grain before the recommended planting date for your area.
6. Plant rye or a Hessian fly resistant wheat for grazing.
7. Granular insecticides applied in-furrow at planting should be applied on susceptible varieties especially if the field has a history of Hessian fly damage or if wheat for grain production is planted before the recommended planting date. Do not apply Di-Syston 15G^R to wheat grown for grazing.

Disease Management

Diseases can be a serious problem affecting wheat. Wheat disease management should begin with varietal selection, not with a fungicide treatment. High-yielding varieties with good disease and insect resistance will complement other pest management practices and possibly reduce the need for fungicide applications. Maintaining yield and reducing inputs increase profits. Resistant varieties can result in reduced pressure for fungicides during heavy disease years. The most desirable varieties are high yielding with good resistance to diseases and insects. This is not always an option; therefore, be aware of what problems are likely. When choosing a variety for disease resistance, select a variety with good resistance to leaf rust, followed by good resistance to glume blotch. These two diseases pose the greatest threat to wheat yields.

Populations of the fungi-causing diseases such as leaf rust and powdery mildew are constantly changing. There are numerous strains or races of these fungi. When a new variety is released, it is usually resistant to the most commonly-occurring races of the fungi prevalent at that time. (But the race population changes rapidly.) Other or new races may become more common. If a variety is not resistant to these races of the fungus, it can become severely diseased. This may happen within a year or two of the release of a new variety. Therefore, it is imperative that producers monitor disease incidence and severity in each field. If resistance is breaking down, you should be aware of this and take steps to adjust for this next year.

Do not consider fungicide applications until certain criteria are met. If used correctly, fungicides can prevent economical yield reduction. If used improperly, fungicides result in wasted money. First determine if the problem is a disease and not due to fertility, environment, insects, etc. Crop records (inputs, varietal resistance, yield potential, etc.) and disease pressure indicate if a fungicide treatment is needed. It is essential to determine the incidence (presence) and severity of each disease in every field. Disease guides that include a description and color photograph of the various wheat diseases will help you identify problems in the field and whether a fungicide application is needed. A point system is provided later in this publication as an aid in determining the need for a fungicide application.

Diseases Commonly Found in Georgia Wheat

Fungal Diseases

Glume Blotch

Biology and Disease Cycle

Glume blotch is caused by the fungus Stagonospora nodorum. Primary inoculum is produced on straw, seed and volunteer wheat. The fungus grows optimally when temperatures are between 68-75 degrees F. Growth is limited when temperatures are below 40 or above 90 degrees F. Infection may require up to 16 hours of wetness. Spores (conidia and ascospores) of the fungus are disseminated by splashing rain or wind. The fungus is able to penetrate directly through wheat tissue or stomata. Certain spores of the fungus are able to survive for months between 35-50 degrees F. Non-wheat hosts do not appear to be important in glume blotch epidemiology.

Figure 17. Septoria on a wheat leaf.		Figure 18. Septoria Glume Blotch.

Symptoms

Initially, lesions (spots) caused by S. nodorum are usually small water-soaked spots. As the fungus continues to develop, these lesions become dry, yellow, and finally red-brown. Most lesions are surrounded by a yellow halo. Older lesions may contain small, black dots in their centers. These structures are called pycnidia, the reproductive structures of the fungus. Pycnidia contain thousand of fungal spores, which perpetuate epidemics. Under favorable weather, lesions continue to expand and finally the entire leave will be necrotic. While initial symptoms are present on the lower foliage, lesions can be present on all aerial parts of the plant during the latter stages of disease development. The most severe infection is typically on the lower foliage.

Head symptoms can appear on the glumes or flower and seed coverings. Lesion are initially tan or brown, but glumes remain green. As the head matures, it will become purplish to black in appearance.

Control

Glume blotch is controlled using the following: (1) Resistant cultivars, (2) High quality disease-free seed, (3) Wide row spacing (allows more air movement), (4) DO NOT overfertilize, (5) Destroy infested straw, (6) Rotation (wheat every third year), and (7) Fungicides.

Leaf Rust

Biology and Disease Cycle

Leaf rust is caused by the fungus Puccinia recondita. Optimal fungal growth occurs between 59-72 degrees F, when moisture is present. Infection occurs in six to eight hours when conditions are favorable, and secondary inoculum (new spores) is produced 7 to 10 days later. Fungal spores are wind disseminated long distances. Multiple races of this fungus exist (i.e., a variety may be resistance to one race of the fungus, but not another race). Epidemics that occur before or during flowering are most detrimental. In addition to reducing yield, rusted wheat is less palatable and sometimes mildly toxic to livestock. Of the diseases affecting Georgia's wheat, rust has the most devastating potential.

Figure 19. Wheat Leaf Rust.

Symptoms

The most diagnostic characteristic of rust is the presence of the fungal spores. Leaves infected with the rust fungus have reddish-orange colored (rust) pustules. Rubbing an infected leaf will leave rusty-colored areas on your fingers.

Rust pustules will vary in appearance depending on the resistance conferred by the variety. Symptoms on susceptible varieties usually begin as small chlorotic flecks. Under favorable conditions, the flecks will quickly enlarge and develop to rust colored pustules, sometime with yellow halos. Symptoms on resistant varieties may be small to large chlorotic spots which never develop into pustules. On some resistant varieties the rust fungus produces very small pustules (i.e., less rust spores).

Control

Leaf rust is controlled through the following: (1) Resistant cultivars, and (2) Fungicides.

Powdery Mildew

Biology and Disease Cycle

Powdery mildew is caused by the fungus Erysiphe graminis. Primary inoculum is produced on infected straw. The fungus develops best when temperatures range between 59-72 degrees F. Development is markedly reduced at temperatures above 77 degrees F. The fungus does not need free moisture to develop. Spores of the fungus are disseminated by the wind. The fungus can penetrate directly through the wheat tissue. This disease usually has little or no effect on Georgia's wheat yields.

Figure 20. Powdery mildew on wheat.

Symptoms

All parts of the plant may be infected by the fungus. The most diagnostic characteristic of powdery mildew is the presence of the whitish to gray fungus on the plant surface. Initial symptoms may begin as small chlorotic spots. Symptoms are usually most prevalent on lower foliage. Under favorable conditions (i.e. high fertility and rapid plant growth) varieties with "good" resistance can become heavily infected. As the lesions (spot) age, small black dots (fungal reproductive structures) may be found in the center.

Control

Powdery mildew is controlled through the following: (1) Resistant cultivars, (2) Fungicides, (3) Rotation, and (4) Destruction of host debris.

Take-All

Biology and Disease Cycle

Take-all is caused by the fungus Gaeumannomyces graminis var. tritici. The fungus survives in infected hosts and host debris. Infection can occur throughout the growing season, and ideal temperatures for infection range between 50-68 degrees F. The disease is favored by neutral to alkaline, infertile (nitrogen- and phosphorus-deficient), and poorly drained soils. Fields planted to wheat two or more years are at more risk than rotated fields. This fungal disease builds up in the soil when wheat is planted in the same field two or more years.

Figure 21. Symptoms of Take-All at the base of the stem.

Symptoms

Mildly-infected plants usually do not exhibit symptoms. Severely-infected plants are stunted and ripen prematurely. Heads are whitish-gray in color. Roots and crown are rotted, brown to black in appearance, and brittle. Plants are pulled easily from the soil. Roots are damaged progressively during the winter and early spring. Shortly after heading infected plants wilt and die because of lack of water conduction from the rotted roots. Areas of dead plants are circular or follow tillage patterns indicating movement of infested crop debris.

Control

Take-all is reduced by rotation with oats, fallow, or other non-cereal winter crops. Rotation with barley, rye, or triticale maintains the fungus in roots of these crops although they may not exhibit symptoms as severe as on wheat. Sorghum as a summer crop will reduce the disease in a subsequent wheat crop, whereas soybeans favors take-all. Other control measures include planting near the end of the recommended period to reduce fall infection and avoiding soil pH above 6.5.

Listed below are the conditions that are most favorable for the development of the major diseases affecting wheat in Georgia (Table 11).

Virus Diseases

Among the disease problems, viruses pose the most troublesome due to a lack of good control methods. Resistant varieties are the only means of control. Identification of the virus, lack of inoculum for effective testing and expense of detection make it very difficult to identify virus-related problems and develop effective prevention programs.

Three viruses have been found to infect soft red winter wheat in Georgia: soilborne wheat mosaic, wheat spindle streak and barley yellow dwarf. Most varieties grown in Georgia today demonstrate good tolerance to soilborne wheat mosaic and wheat spindle streak. Little is known though of the differences in variety tolerance or resistance to barley yellow dwarf.

The symptoms of soilborne wheat mosaic virus range from mild green to a prominent yellow leaf mosaic. Plants may appear to be stunted or rosette in shape. Symptoms are usually seen early in the season. New leaves may be mottled or exhibit streaks or flecking.

The wheat spindle streak mosaic virus was identified several years ago in Georgia. The symptoms vary from variety to variety, but usually plants will appear stunted with mottled and streaked leaves. Leaf streaks are usually a light green to yellow discontinuous formation. The discontinuous streaks run parallel to the leaf veins and taper to form a chlorotic spindle. The virus is transmitted by a fungus. Usually the virus is a problem after long periods of wet, cool soils.

The barley yellow dwarf virus is probably the most widely-distributed virus in wheat. Barley yellow dwarf virus is estimated to reduce yields by 5 to 25 percent. Symptoms are somewhat ambiguous and are often overlooked as a nutritional problem or frost damage. Usually the discoloration is characterized by various shades of yellow or reddening from the tips to the base and from margin to the midribs. Severe infection usually cause some stunting and reduction in numbers of seeds per head. BYDV is transmitted by a host of aphid species. Aphids acquire the virus by feeding on infected plants for very short periods and then move to other uninfected plants. Symptoms may vary depending on variety. Infection of the virus can occur any time when viruliferous aphids multiply and migrate in fields.

This virus has caused severe loses during the last years in many Georgia fields. In a survey the spring of 1993, 100 percent of the fields surveyed (36 in Georgia and 20 in Alabama) were found to be infected with BYDV. Severity ranged from slight to severe. Studies are currently being conducted to determine an effective control program to reduce the incidence of BYDV.

Fungicide Use

Fungicides can only be effective when you carefully select the fungicide with good activity against the disease(s) present. They should be applied at the correct rate and time according to the label. Fungicides should be applied with enough water to get good coverage: 5-7 gal/acre for aerial and 20-30 gal/acre for ground application. Use of a spreader-sticker will help improve leaf retention and fungicide performance. When applying fungicides, always read the label and comply with the instructions and restrictions listed.

Generally, the most effective time to apply fungicides is from flag leaf emergence to early heading, but be certain to follow any label restrictions on time of application and the number of applications. Refer to the "Wheat Foliar Fungicide Point System" to aid in decision about making fungicide applications.

Making Spray Judgements

Scout each individual field beginning at Feekes' GS 5 on a weekly basis. At, or just before stage 7, make a disease evaluation. Then use the point guide to determine the need to spray.

If a "zero" is indicated in any major category (I-VII), then it will probably not be profitable to spray.

When to spray: Generally the most effective time of fungicide application is at flag leaf emergence (Feekes' GS 8-9). Additional applications through Feekes' GS 10.5, flowering, may sometimes be beneficial, particularly for control of Septoria glume blotch.

When using a fungicide observe the following precautions:

1. Observe all directions, restrictions and precautions on pesticide labels. It is dangerous, wasteful and illegal to do otherwise.
2. Store all pesticides in original containers with labels intact and behind locked doors. "KEEP PESTICIDES OUT OF THE REACH OF CHILDREN."
3. Use pesticides at correct label dosage and intervals to avoid illegal residues or injury to plants and animals.
4. Apply pesticides carefully to avoid drift or contamination of non-target areas.
5. Surplus pesticides and containers should be disposed of in accordance with label instructions so that contamination of water and other hazards will not result.
6. Follow directions on the pesticide label regarding restrictions as required by state and federal laws and regulations.
7. Avoid any action that may threaten an endangered species or its habitat. Your county Extension agent can inform you of endangered species in your area, help you identify them, and through the Fish and Wildlife Service Field Office, identify actions that may threaten endangered species or their habitat.

Weed Management

A good weed control program is essential to produce profitable high wheat yields. Weeds reduce yields by competing for nutrients, sunlight and moisture. They also reduce your profits by contaminating your grain with seed which results in dockage and a reduction in price at the elevator.

Survey wheat fields and you will likely find many different weed problems such as wild radish, wild garlic/onion, annual Italian ryegrass, common vetch, henbit, chickweed, curley dock and little barley. In the spring you may also see common ragweed, cutleaf evening primrose, pigweed and thistles. However, the most problem weeds are wild radish, wild garlic and annual Italian ryegrass. These weeds can reduce your yields over 50 percent if left uncontrolled. Therefore, it is very important to control these weeds effectively and efficiently.

Controlling weeds in wheat may be one of the most difficult management practices in cultivated crops. While there are several chemical choices for broadleaf weeds, there is only one for grass control. This doesn't necessarily make it difficult. Timing is critical because weather-related problems often interfere with applications. Delayed chemical applications increase the cost of weed control simply because herbicide rates have to be increased because weeds grow larger with time. This can reduce control because winter weeds are more difficult to control as they get larger. Some producers stretch the window of application too wide which results in poor weed control and crop injury. Wheat plants are very susceptible to injury by some herbicides as they enter the reproductive phase.

Planning ahead will prepare you to take advantage of the options available during the growing season. The key factors in a good weed control program are (1) recognizing your weeds, (2) choosing the right herbicides, (3) timing the application for best control of the target weed by adjusting for crop growth stage, (4) using the correct rate, (5) reading and abiding by all label restrictions.

Cultural Control Methods

Cultural weed management is probably the single most important factor in reducing weed pressure in wheat. Using certified seed ensures quality, weed-free wheat seed. Proper seed-bed preparation, fertilization, insect and disease control help ensure a healthy crop and allow the wheat to shade the soil surface and out-compete many weeds.

Another important aspect is to control the transfer of weed seed from field to field during harvest. Be sure to clean your equipment when moving from heavily weed-infested areas. Commercial combining operators which travel long distances can introduce new weed species into clean areas.

Site selection can play a significant role in wheat weed control. Some of the worst weeds in wheat include annual Italian ryegrass and wild radish. Rotation away from fields with heavy infestations of these weeds will aid weed control. In addition, this allows for alternative crops and control methods (herbicides) that can reduce the populations of these weedy species. This also reduces the development of herbicide resistant weeds. Annual Italian ryegrass shows resistance to Hoelon in some areas of Georgia.

Chemical Weed Control

Once wheat has begun to germinate, it is necessary to properly identify the weeds. This should occur soon after the weeds emerge because larger weeds are harder to control (sometimes impossible) and will have already caused some yield loss. The primary weeds infesting Georgia wheat include: wild radish, wild mustard, wild turnip, Italian (annual) ryegrass, wild onion and garlic. Table 12 lists distinguishing characteristics for these weeds.

The stage of development of the wheat plant, particularly with regard to tillering is an important factor in chemical weed control. Many herbicides used in wheat can only be applied during certain stages of wheat development to avoid crop injury. Many of the herbicides wheat affect the growth of the target weed, either through physiological or metabolic mechanisms. Therefore, the better the plant is growing, the better the control. Applications made to weeds when wheat is stressed in some fashion (drought or wet soil) will often result in decreased control. In addition, stress to the wheat plants may reduce the tolerance to the herbicide treatment, resulting in crop injury.

Broadleaf Weed Control

Several options exist for broadleaf weed control in wheat including phenoxy and sulfonyl urea type compounds. The phenoxy herbicides consist of 2,4-D and MCPA while the sulfonyl ureas include tribenuron (Express) and tribenuron + thifensulfuron (Harmony Extra). Bromoxynil (Buctril) and MCPA + bromoxynil (Bronate) are also registered.

MCPA and 2,4-D cause a twisting or downward cupping of susceptible plants. They are primarily absorbed by the foliage, providing very good weed control if applied at the proper time. These compounds are growth regulating substances, killing weeds by inducing rapid, uncontrolled growth. They can however, cause injury to the wheat if not applied at the proper time. The critical period for phenoxy applications is after tillering and before jointing or stem elongation. Injury may result if 2,4-D is applied to very small wheat (2 tiller or less). Injury symptoms are stunting, reduced tillering, twisting and a "rat-tail" effect (leaves do not unfold). If a phenoxy compound is applied after stem elongation, the internodes and heads will twist and be deformed, thus reducing yields and profits.

It is important to remember that small weeds are easier to control; soon after full tiller development will be the best time for good weed control. Research shows that wild radish is effectively controlled in the rosette stage at less than 6 inches in diameter. Once the wild radish plant has begun to bolt, or elongate the flower stem, control becomes difficult. On larger wild radish plants, 2,4-D is more effective than MCPA, but MCPA is often less injurious to wheat than 2,4-D.

Bromoxynil will provide good broadleaf weed control and should be applied to wheat before the boot stage. However, for good control of wild radish with bromoxynil the weeds must be less than 1/2" in diameter with less than four leaves.

The sulfonylurea herbicides (Express and Harmony Extra) are absorbed by the foliage and roots of plants and inhibit protein synthesis within susceptible plants. This causes the weeds to cease growth and eventually die. Basically, these herbicides cause the plant to starve to death and this often takes two to several weeks for complete death to occur. Because coverage is essential, always use a non-ionic surfactant with the sulfonylurea herbicides.

Both Express and Harmony Extra can be applied after the wheat has two complete leaves and before the third node stage. They have the advantage over the phenoxy-type compounds because they can be used after jointing but may not be the most cost-effective treatment. Express and Harmony Extra will both provide good control of wild radish, but Harmony Extra is also effective on other broadleaf weeds such as henbit and wild garlic. As with the phenoxy herbicides, smaller weeds are more easily controlled.

Grass Weed Control

Grassy weed problems in wheat are primarily limited to annual Italian ryegrass (Lolium multiflorum). This species is widespread throughout Georgia and the southeast. Ryegrass is a highly competitive grass and can reduce wheat yield by more than 50 percent if left uncontrolled. Therefore, successful ryegrass control can be a vital element in producing wheat in Georgia. Italian ryegrass is an annual and is spread primarily by seed. Management practices to reduce seed spread will greatly decrease ryegrass problems. Such practices could include: cleaning equipment from field to field (especially those fields heavy in ryegrass), maintaining clean fence rows and ditch-banks surrounding the fields and avoiding those fields with heavy ryegrass populations. Burning after harvest may help to reduce seed numbers, but little research has been performed in that area.

Currently, Hoelon (diclofop) is the only chemical labelled for annual Italian ryegrass control in wheat. This herbicide is readily absorbed by the ryegrass leaves and roots and inhibits fatty acid synthesis. Fatty acids are essential components of the plant cell membrane and susceptible plants will die slowly (two to three weeks), similar to the sulfonylurea herbicides.

Hoelon can be used pre or postemergence. Unless the field has a history of heavy ryegrass infestation, an early postemergence application will be the most cost-effective treatment. When the ryegrass is small (1 to 3 leaves), lower rates of Hoelon will provide good control. However, larger ryegrass plants will require a higher dosage and, in many cases, control will not be complete. It is important to remember that applications of Hoelon before, during or immediately after cold, wet weather will decrease weed control and increase crop injury.

Control of ryegrass with Hoelon may be improved with the addition of crop oil concentrate, but may result in yellowing of the wheat crop. Under proper growing conditions, this should not be a problem. In addition, DO NOT mix Hoelon with broadleaf herbicides. This will cause decreased weed control, particularly ryegrass. A word of caution is important. Repeated uses of Hoelon on a field over years may lead to Hoelon resistant ryegrass. Therefore, crop rotation must become an important element in the sustained, effective control of Italian ryegrass.

Liquid Nitrogen Tank-Mixes

Many farmers will combine topdress nitrogen applications with herbicide treatments. In many cases this technique is quite effective, but timing is critical. The best rule of thumb is to apply the herbicide when the weeds are small and the wheat will not be injured. If the two applications coincide, a tank-mix is possible. However, stretching the window for effective weed control to accommodate nitrogen fertilization may result in poor weed control. If nitrogen applications are applied to stimulate tillering or after jointing, injury and loss of yield will result from the addition of a phenoxy herbicide.

The key to successful weed control in wheat is management. Tools and knowledge exist for effective, economical weed control but only through proper implementation can this be achieved. Knowing the developmental stage of the wheat, size and types of weeds present, and the proper herbicide and rate to use determine the success of a good weed control program.

Check the current extension Georgia Pest Control Handbook for up-to-date chemical and rate recommendations.

Plant Growth Regulators

Growth regulators are used in an attempt to reduce lodging problems often associated with high-yield wheat production. Lodging results in delayed harvesting, decreased grain recovery and poor grain quality. There are many management factors that influence the potential for lodging: (1) variety selection, (2) nitrogen management, (3) precision seeding, and (4) nutrient management.

In Georgia studies, yield response to plant growth regulators has been observed very infrequently. The plant growth regulator, Cerone^R, is the only plant growth regulator labeled for wheat in the Southeast. Only when the potential for lodging is high should the growth regulator be considered for use. Those parameters would be (1) a variety that is susceptible to lodge, (2) applications high N rates on soils with high residual soil nitrogen. (3) very high stem density at flag leaf emergence. Carefully read the label and follow all directions. A plant growth regulator should not be considered if these parameters are not present.

Dollars and Cents of High-Yield,
Intensive Wheat Production

A review of state average wheat yields and average market price gives the impression that wheat production in the state has been marginally profitable during recent years.

The average yield per acre has been near 40 bushels the last few years. And with market prices being relatively low due to more than adequate supplies of the grain, net profit from the crop has not been competitive with many other field crops. But wheat is still grown in the state. Why?

For two reasons. First, the wheat program provisions of the previous farm bill provide a target price for program wheat to be profitable.

Second, many growers achieve yields well above the state average. Yields of 50, 60, and 70 bushels per acre (and higher) are now commonly reported.

A review of wheat yields in Georgia (Figure 1) indicates a general upward trend since 1986, and particularly since 1989. While favorable weather is a major factor in this trend, Georgia wheat growers are also becoming more familiar with production practices that encourage higher yields and adopting those practices.

Comparison of Wheat Systems

A cost estimate of producing wheat using traditional practices indicates a cash outlay of $90-100 to grow an acre of the grain. Major cost of production items are fertilizer, machinery and labor inputs. The expected yield with this system is in the 35-40 bushel per acre range.

But research and first-hand production experience demonstrate that the crop is responsive to higher levels of fertilizer and to fungicides and insecticides to control invasive elements than can lower yield.

The addition of these added inputs and the expertise to manage these inputs are referred to as an intensive system of production.

An analysis of these added inputs indicate approximately $60 more annual costs per acre are required to grow wheat under the intensive system. These added costs, in conjunction with higher managerial expertise, provide an estimated yield of 75 bushels per acre.

The intensive production system incurs slightly higher fixed costs than the conventional system due to a bit more machinery use. These costs are included in the final profit analysis. But for comparing the two systems, the added cash costs (compared with added returns) are the major basis for analysis.

Added Costs of Intensive System

For comparative purposes, the major estimated "added per acre costs" in 1994-95 for this production system are:

Minor added outlays include extra drying costs, more interest expenses and added allowances for general overhead and management.

To illustrate the importance of the relationship between these added costs and added production, the bushels of wheat needed to cover the costs of the additional inputs are shown in Figure 22.

Figure 22. Bushels of wheat needed @ $3/bu. to cover intensive system extra costs

With a wheat market price of $3.00 per bushel, we estimate it would require 6.5 bushels of wheat for example, to pay for the added fertilizer of the intensive system. Considering all added cash inputs, it would require approximately 20 bushels of wheat to pay for these costs.

If the system achieves an additional 35 bushels of yield, then net to the farm operator would be 15 bushels. This would be the amount of the extra profit. A higher wheat price would decrease the number of bushels required to pay the extra costs.

The overall analysis in Table 13 shows a lower cost of production per bushel for the intensive system ($2.78 vs $3.40). This is due to the total added output value being greater than the costs of the added inputs. Table 14 illustrates the cost per bushel of different yield levels at various production costs.

These costs estimates are based on what we feel is the current state of production technology and that of higher levels of management. They may not apply to all farm operators. But they are a starting point for an economic analysis of growing wheat. Each grower should provide his own costs and expectations.

Harvest Management

Harvest management is an important element in efficient high-yield wheat production. It is one of the last management practices necessary for the sale of high quality wheat; in Georgia, a timely harvest is the key.

Many problems can occur during harvest or with delayed harvest. Declines in test weight result from the rewetting of grain after the crop has physiologically matured. Rainfall or heavy dew after the crop has physiologically matured frequently occurs in Georgia. It is therefore, important to harvest in a timely fashion. Heavy dews and high humidities also lead to head diseases such as scabs which cause vomotoxins. This results in the reduction of food and feed quality.

Delaying harvest till wheat is 14 to 15 percent moisture frequently results in decline in quality. You may consider the cost of drying wheat artificially vs. the discounts received at an elevator in the consideration of removing some grain from the field early to spread your risk at harvest time.

The following are important points to consider prior to, during and after harvest.

• Contamination of clean grain with weed seeds reduce quality and marketability. Keep areas heavily infested with weeds separate from clean grain and harvested at a later time.
• Harvest and sell sprouted grain as soon as possible. Sprout damage infrequently occurs in Georgia but severely reduces quality and profits.
• Monitor sieve and air adjustments. Observe the grain in the bin and continuously check grain moisture to monitor combine efficiency. Frequent checks reduce combine losses.
• Prior to storage, thoroughly clean the bins to reduce problems from storage insects.
• Use a protectant when the grain is stored. Grain insects frequently infest Georgia fields. Monitor the grain regularly and use a fumigant to kill outbreaks in storage.
• Maintain moisture at safe levels (less than 12 percent) for long term storage.
• Set a regular schedule to monitor grain frequently for problems due to insect and fungal pathogen and/or moisture. Regular monitoring is essential to maintaining a quality grain.

Producing and maintaining high quality wheat means paying very careful attention to details. It also means implementing practices during harvest that maintain quality and yield and result in a good product for market. Pay careful attention to combine adjustments and the many environmental factors that reduce quality and yield. Be prepared to harvest efficiently and quickly. For more information on harvesting, drying and grain storage, request the following publications from your local county Extension office.

(1) Small Grain Production and Utilization in Georgia, Bulletin 929.
(2) Measuring Field Losses for Grain Combines, Bulletin 973.
(3) Grain and Soybean Drying on Georgia Farms, Bulletin 873.
(4) Aerating Grain in Storage, Bulletin 712.

Acknowledgements: The authors acknowledge the contribution of Dr. Paul Mask, Auburn University, Dr. Dan Bran, Virginia Polytechnic Institute and State University and the Potash and Phosphate Institute in the preparation of some of the materials used in this publication.

Funding for this publication was provided by The Georgia Plant Food Educational Society.

Prepared by R. Dewey Lee - Extension Agronomist; Boyd Padgett - Extension Plant Pathologist; Randy Hudson - Extension Entomologist; Greg MacDonald - Extension Weed Science

The University of Georgia and Ft. Valley State College, the U.S. Department of Agriculture and counties of the state cooperating. The Cooperative Extension Service offers educational programs, assistance and materials to all people without regard to race, color, national origin, age, sex or disability.

An Equal Opportunity/Affirmative Action Organization Committed to a Diverse Work Force

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, The University of Georgia College of Agricultural and Enviromental Sciences and the U.S. Department of Agriculture cooperating.

Gale A. Buchanan, Dean and Director