Blueberry Research

At the University of Georgia

1999 Annual Research Update

D. Scott NeSmith, Editor

Table of Contents

Preface
List of Contributors to Georgia Blueberry Research for 1999
Development of Southern Highbush and Rabbiteye Blueberry Cultivars Adapted to Georgia
Firmness of 'Brightwell' Rabbiteye Blueberry in Response to Various Harvesting and Handling Procedures
Response of Some Rabbiteye and Southern Highbush Blueberries to Mechanical Harvesting
Use of a CPPU in Combination with Gibberellic Acid on Rabbiteye Blueberries
Irrigation Requirements of Mature Rabbiteye Blueberries
Moderate Post-harvest Hedging of Mature 'Tifblue' Rabbiteye Blueberries
Studies on Enhancing Establishment of Rabbiteye Blueberries
Response of 'Brightwell' Rabbiteye Blueberry to Self and Cross Pollination
Retain Increases Firmness of Some Blueberry Cultivars
Comparison of Frequent 10-10-10 Applications with a Single Slow-Release Meister Fertilizer Application on the Growth of Young 'Reveille' Blueberries in Amended Strips
Georgia Blueberry Pest Management Survey
An On-Farm Pruning Experiment with 'Climax' Blueberries
CPPU Enhances Fruit Set and Fruit Size of Some Blueberry Cultivars
Ethephon Bloom Delay Experiments on 'Climax' and 'O'Neal'
Optimizing Spray Schedules for Control of Mummy Berry on Rabbiteye Blueberries in Georgia

Preface

This report is an effort to compile, annually, summaries and updates of blueberry research projects being conducted in Georgia. The projects included here do not necessarily represent all blueberry research efforts. The intent of the report is to provide researchers, extension personnel, industry cooperators, and constituents a simple means of perusing contemporary research projects concerned with blueberries. Results reported herein are largely preliminary, and should not be considered as firm recommendations. Some agrichemicals mentioned may not be labeled for use in blueberries, and this report should not be considered a recommendation for using these.

Data herein presented are property of The University of Georgia College of Agricultural and Environmental Sciences and the author, and these cannot be duplicated, published, or included in any form of advertisement or endorsement without the written permission of the author. Inquiries should be directed to the author, or to:

Dr. D. Scott NeSmith
Department of Horticulture
The University of Georgia
Georgia Station
Griffin, GA 30223-1797
Phone: (770) 228-7243
FAX: (770) 412-4764

snesmit@griffin.uga.edu

Mention of trademark or proprietary names in this report is descriptive and does not imply endorsement of the product. Inclusion of summaries and preliminary results should not preclude future publication of the completed research.

List of Contributors to Georgia Blueberry Research for 1999

The following alphabetical listing of farms, companies, and organizations are greatly appreciated for their fiscal support of blueberry research efforts in Georgia during 1999. The list may inadvertently omit some contributors, and apologies for such errors are made in advance. Some of the contributors assisted with multiple research projects.

• Abbott Laboratories
• Appling Farms
• Baxley Sunbelt
• B.E.I.
• Griffin Corporation
• Helena Chemical
• MBG Marketing
• Rohm & Haas Company
• Wade Farms
• Zeneca Ag Products

Development of Southern Highbush and
Rabbiteye Blueberry Cultivars
Adapted to Georgia

D. Scott NeSmith

The UGA Blueberry Cultivar Development Program

Blueberry breeding and cultivar development efforts in Georgia over the past four decades have largely involved rabbiteye blueberries (Vaccinium ashei Reade). Rabbiteye blueberries are well adapted to many soils in Georgia, and their continued use by the industry is expected. Thus, the cultivar development program at The University of Georgia continues to generate and evaluate rabbiteye selections.

In addition to rabbiteye cultivars, grower interest in southern highbush (Vaccinium corymbosum L.) blueberries is rapidly increasing. Southern highbush blueberries are desirable because they have high quality, early ripening fruit; however, the species of blueberry is limited by production problems which are largely soil related in the Southeast. There is considerable need in Georgia for southern highbush cultivars that have high quality, early season fruit, and that can be produced on atypical highbush blueberry soil. The Georgia Blueberry cultivar development program is currently generating and evaluating many selections of southern highbush, but only the cultivar 'Georgiagem' has been released (released in 1987).

Summary of 1999 Observations

The 1999 growing season provided another excellent opportunity to evaluate numerous rabbiteye and southern highbush blueberry selections at Alapaha. There was some thrip damage to flowers of late blooming selections and cultivars, which greatly reduced fruit set and yield for these. However, the early to mid-season selections and cultivars had good fruit set this year, and there were no problems related to spring freezes (as occurred in 1998). Chill hours were well below average for the year, with only 400 hours accumulating by February 15. Thus, selections experienced some "selection pressure" in chill hour adaptation. Comprehensive flowering notes, cropping notes and fruit characteristic evaluations were taken for more than 200 selections of rabbiteye and southern highbush blueberries, as well as numerous cultivar standards. Following is a summary of findings and observations for 1999.

Rabbiteye Blueberries

Rabbiteye blueberries make up the greatest number of selections at the Alapaha blueberry research farm. During 1999, these selections were carefully evaluated with special emphasis on time of flowering, time of ripening, crop load, fruit size, fruit firmness, and plant vigor. Table 1 presents a summary of evaluations for 5 rabbiteye standard cultivars and 14 numbered selections. The numbered selections are those that were superior in certain traits during 1999. A discussion of some of these traits follows.

Flowering Time: There was no problematic freeze during the late spring of 1999. However, in past years selections having flowering dates before March 15 typically experience flower injury from spring freezes. A notable selection for late flowering is T-378, which had 50 percent open blooms on April 4. This late flowering date should be of great benefit in years when spring freezes occur. T-378 continues to be a very exciting discovery in that not only does it bloom late, but it also ripens early (50% ripe by June 2). In 1998, T-378 bloomed April 15 and ripened June 3. Flowering dates (50% open blooms) for standard cultivars in 1999 were March 24 for 'Austin,' March 16 for 'Climax,' March 29 for 'Brightwell,' March 28 for 'Premier,' and on March 30 for 'Tifblue.' The low chill hours in 1999 did cause some delayed blooming for some selections; however, most were able to flower adequately in response to the low chill hour year. Selections and cultivars that bloomed around the time of 'Tifblue' experienced considerable flower damage from a thrips infestation, which subsequently affected fruit set and yields.

Ripening Time: Georgia growers are very interested in rabbiteye blueberries that ripen in the last two weeks of May and the first week of June. As of now, the best they have is 'Climax' and 'Premier,' which both had 50 percent ripe fruit by June 2. The newest released cultivar from Georgia is 'Austin,' which had 50 percent ripe fruit by June 8. Some selections showed great promise in achieving earliness equal to or even earlier than the current industry standards, but with more reliable cropping. The most notable early maturing rabbiteye selections were T-366 (50% ripe by May 28), T-541 (50% ripe by May 31), and T-579 (50% ripe by May 27). T-366 had the best overall crop of these, which was similar to last year. The selection T-584 ripened with 'Climax' but was far superior to the standard in cropping and several fruit attributes. T-256 is a noteworthy selection that had an early crop and high yield. This selection is strongly being considered for release as a companion to 'Austin.' While most interest is in earliness, there is still interest in later maturing, high yielding rabbiteye blueberries. A notable late selection in 1998 was T-105, which had the best rabbiteye crop of all selections last year. The selection was late maturing in 1999, but crop load was much less than in 1998 (likely due to thrip damage).

Fruit Size: Rabbiteye blueberry fruit are generally considered to be small compared to highbush blueberry fruit. Large-fruited selections of rabbiteyes were noted at Alapaha in 1999. Those selections which had very large fruit included T-300 and T-451. These selections had fruit that exceeded 20 mm in diameter. 'Premier' was the only industry standard that had fruit approach-ing this size, yet it had a very small crop load in 1999. T-431, T-459, T-541, and T-546 all had fruit larger than 'Premier.' T-300 was especially appealing, as it also had a high degree of firmness.

Fruit Firmness: Firmness of fruit continues to be of great importance for rabbiteye selections. Firm berries can generally be mechanically harvested better than softer berries, and the firmer fruit also has a much better post-harvest quality. While most rabbiteye cultivar standards have acceptable firmness, there were some selections that were even more superior. Those selections having exceptional firmness were T-300, T-366, T-431, T-459, and T-546. Of these, T-366 is the most exciting because it also had an early maturing crop, and crop load was very good.

Yield: Yields were taken for several early, mid, and late season rabbiteye selections along with data for cultivar standards. The data from 1999 are depicted in Table 2, along with data from 1998. The early season standard 'Climax' had only 6.2 lbs/bush in 1999, which was very similar to yields in 1998. 'Austin' had extremely high yields in 1999 (17.6 lbs/ bush). This new release continues to show promise for surpassing 'Climax' as the early season rabbiteye of choice. Other early rabbiteyes with high yields in 1999 were T-256 and T-584 (both had 13.4 lbs/bush). As for mid-season blueberries, 'Brightwell' yielded very high during 1998, but only moderately well in 1999. The selections T-397, T-431, and T-459 all yielded better than 'Brightwell' in 1999. T-501 had high yield in 1998, but yield was extremely low in 1999. This may have been due to thrip damage to some extent, but it could also be related to over-cropping in 1998. T-431 was a good performer in both 1998 and 1999, and the fruit quality is far superior to 'Brightwell.' 'Tifblue' (late season rabbiteye) yield for 1999 was low, supposedly due to thrip damage. A similar response was observed for T-105 in 1999. T-459 was one of the few selections that maintained very good fruit size over the course of all harvests, as it did in 1998 also.

Southern Highbush

There are a substantial number of southern highbush blueberry selections at the Alapaha blueberry farm. These selections were carefully evaluated for time of flowering, time of ripening, crop load, fruit size, fruit firmness, and plant vigor. Table 3 is a summary of evaluations for 3 standard cultivars and 10 numbered selections. The numbered selections were those that exhibited outstanding traits during 1999. A discussion of these follows.

Flowering Time: As with the rabbiteye selections, a March 15 or earlier bloom date can result in severe injury to flowers in years with late spring freezes. Some selections that had late 50 percent bloom dates were TH-164 (April 8), TH-442 (March 30), and TH-251 (April 2). It is likely that a late spring freeze would have little impact on flowers of these selections. TH-164 was especially noteworthy, because it not only bloomed late, but it also ripened by May 20. Comparing these flowering times to standard cultivars, 50 percent open blooms occurred on March 20 for 'Georgiagem,' on March 15 for 'O'neal,' and on March 3 for 'Sharpblue.'

Ripening Time: Most southern highbush selections and cultivars at Alapaha ripened between May 5 and June 1 in 1999. TH-471 was a notable selection which was 50% ripe by May 16. TH-279 had very concentrated ripening, which began on May 7 and was completed by May 22. TH-442 was impressive in that it flowered late and ripened early (50% ripe by May 22). The standard cultivars 'Georgiagem,' 'Sharpblue,' and 'O'neal' had 50 percent ripe fruit from May 19 to May 25. 'Sharpblue' had an exceptionally good crop in 1999, probably because there was no late spring freeze.

Fruit Size: Southern highbush blueberries generally have acceptable fruit size, but there were differences among the many selections. The standard cultivars 'Sharpblue' and 'O'neal' had fruit 19 mm in diameter, which is considered to be large. Some selections having fruit size greater than these standards were TH-621, TH-622, and TH-623. These 3 selections had other fruit attributes such as scarring, color, and firmness that were superior to 'O'neal' and 'Sharpblue.'

Fruit Firmness: As with rabbiteyes, highbush fruit firmness is considered to be of utmost importance for harvesting and post-harvest quality. 'O'neal' had the best firmness among the standard cultivars; however, there were several selections with equal firmness. The fruit of TH-622 was very firm, and the selection also had favorable ratings for fruit size, color, and scarring.

Plant Vigor: One of the greatest hindrances to growing southern highbush blueberries in Georgia is their lack of vigor, especially on a wide range of soils. The soil at Alapaha is not considered "good" highbush soil, so selections showing good vigor at the site would likely do well on other sites. None of the southern highbush standard cultivars display a high level of vigor at Alapaha; however, the selections TH-279, TH-471, TH-473, TH-621, TH-622, and TH-623 are very vigorous. These selections have established easily at Alapaha, and continue to grow vigorously after a number of years.

Yield: Yield of some of the highbush was determined for the first time at the UGA Research Farm in 1999 (Table 4). Again, the interest in southern highbush is largely driven by earliness and high quality fruit. The first harvest was made on May 6, 1999. The selection TH-471 and the standard cultivar 'Sharpblue' were the only plants with significant ripe fruit on this date, with 1.0 and 1.7 lbs/bush harvested for the selections, respectively. By May 13, TH-279 was also harvested, but 'Georgiagem' was harvested the first time on May 19. 'Sharpblue' had a good crop in 1999, as did the selections TH-471 and TH-279. Fruit size of 'Sharpblue' was larger than TH-471 on all harvest dates, but TH-279 fruit size equaled that of 'Sharpblue.' TH-279 ripening was more concentrated than 'Sharpblue' or TH-471.

Goals of the UGA Blueberry Cultivar Development Program for 2000

The 1999 growing season was a good year for evaluating blueberry selections at Alapaha. Plans for the year 2000 are to continue aggressively evaluating seedlings, advanced seedlings, selections, and advanced selections of both rabbiteye and southern highbush blueberries. More than 2500 seedlings were generated from crosses made at UGA and by USDA personnel in 1998. These seedlings were planted in a seedling nursery in 1999 and will be grown for future evaluations. More than 1000 blueberry seed-lings were planted in a nursery bed in 1998. These seedlings will be screened during 2000 for fruit characteristics including size, scar, firmness, color, and flavor. The most promising seedlings will be identified as advanced seedlings for further evaluation (estimated at 2-3% of total seedlings). In 1998, approximately 30 seedlings were identified as advanced seedlings from 1996 and 1997 crosses. These advanced seedlings were planted in the field at Alapaha in 1999 and will be further evaluated as potential selections in 2000. In addition to the seed-ling and advanced seedling evaluation, more than 100 selections currently growing at Alapaha will be evaluated during 2000 for possible designation as advanced selections. In 1999, more than 15 selections were identified as advanced selections and were propagated. These will be further evaluated in 2000 for potential as cultivars, and several of the advanced selections will be distributed to cooperators to assist in the evaluation process. Three rabbiteye advanced selections were distributed to cooperators in 1999 to begin the final phase of testing for their potential as cultivar releases. Data taken on the advanced selections will include fruit characteristics described above, plant growth characteristics, flowering times, and yields.

Firmness of 'Brightwell' Rabbiteye Blueberry in Response to Various Harvesting and Handling Procedures

D. Scott NeSmith, Department of Horticulture, Georgia Station, Griffin, GA; Stanley E. Prussia, Department of Biological and Agricultural Engineering, Georgia Station, Griffin, GA; and Gerard Krewer, Department of Horticulture, Rural Development Center, Tifton, GA

Fruit firmness continues to be an important quality parameter of blueberries produced for fresh market consumption, as it relates to consumer appeal and to post-harvest decay of fruit (Ballinger et al., 1973; Mainland et al., 1975). Currently, about 25 percent of Georgia's commercial blueberry crop is sold as fresh fruit, with most of the remaining crop being sold for the frozen market. Much of the fresh fruit from Georgia is harvested by hand in order to maintain fruit firmness and quality. As the season progresses, however, hand harvesting becomes less affordable due to falling market prices. As a consequence, many growers convert over to machine harvesting of the crop from mid to late season. The use of mechanical blueberry harvesters often results in much of the fruit being destined for lower profit processed markets due to quality (firmness) losses. However, continued fresh sales of the Georgia crop would increase returns to growers.

Comparisons of machine and hand harvested fruit quality have been made for a few highbush and rabbiteye blueberry cultivars (Austin and Williamson, 1977; Ballinger et al., 1973; Brown et al., 1996; Mainland et al., 1975; Miller and Smittle, 1987; Patten et al., 1988). Many of these studies have shown that mechanically harvested berries are often softer than hand harvested fruit; however, mechanical harvesters have been improved in recent years to address some of the problems relating to lessened fruit quality. Also, newer cultivars better adapted to mechanical harvesting have been developed. The rabbiteye blueberry cultivar 'Brightwell' was introduced in 1981, and has rapidly become a major cultivar for blueberry growers in the Southeast. The ripening time of this cultivar in relation to current fresh market prices puts it just on the economic threshold of converting from hand-harvesting to mechanical harvesting as discussed previously. Currently, both methods are used to harvest the crop, but there has been no research to examine how fruit quality of this cultivar responds to different harvesting and handling procedures. The objective of this research was to evaluate fruit firmness changes of 'Brightwell' in response to various harvesting and handling procedures.

Materials and Methods

This experiment was conducted using 14-year-old 'Brightwell' blueberry plants grown at the University of Georgia's Blueberry Research Farm near Alapaha, Georgia. The plants were non-irrigated and were in excellent health. Plants used for the experiment were a group of 50 plants in a single row that were approximately 7 ft (2.1 m) in height. A series of harvesting and handling treatments were randomly utilized on groups of five to six plants in the row to obtain fruit for firmness measurements. Three experiments were conducted over two harvest periods.

Experiment 1. The first experiment had the following harvesting and handling treatments: 1) hand harvested directly into clam shell, fruit cooled immediately in ice chest, no post-harvest grading or sorting; 2) hand harvested directly into clam shell, fruit kept at ambient temperature for 24 hours, no grading or sorting; 3) hand harvested in field lugs, fruit maintained at ambient temperature, graded and sorted, packed in clam shells; 4) machine harvested, fruit maintained at ambient temperature, no grading or sorting, packed in clam shells; 5) machine harvested, fruit maintained at ambient temperature, graded and sorted, packed in clam shells.

Experiment 2. The second experiment was very similar to experiment 1, except that two additional cool down treatments were added. Experiment 2 had the following treatments: 1) hand harvested directly into clam shell, fruit cooled immediately in ice chest, no post-harvest grading or sorting; 2) hand harvested directly into clam shell, fruit kept at ambient temperature for 24 hours, no grading or sorting; 3) hand harvested in field lugs, fruit maintained at ambient temperature, graded and sorted, packed in clam shells; 4) machine harvested, fruit maintained at ambient temperature, no grading or sorting, packed in clam shells; 5) machine harvested, fruit maintained at ambient temperature, graded and sorted fruit, packed in clam shells; 6) machine harvested, fruit cooled immediately, no grading or sorting, packed in clam shells; 7) machine harvested, fruit cooled immediately, graded and sorted , packed in clam shells.

Experiment 3. The third experiment was a small test to examine the benefit of harvester features such as curtains and padding on fruit firmness. Experiment 3 had the following treatments: 1) machine harvested with curtains and pads intact, fruit maintained at ambient temperature, no grading or sorting, packed in clam shells; 2) machine harvested without curtains, but pads left intact, fruit maintained at ambient temperature, no grading or sorting, packed in clam shells; 3) machine harvested without curtains or pads, fruit maintained at ambient temperature, no grading or sorting, packed in clam shells.

The mechanical harvester used in this experiment was a B.E.I. model LBT (little blue tall), which was provided by Blueberry Equipment, Inc. The harvester was not self propelled, and it had a sway bar fruit detachment system. The harvester was equipped with removable curtains and padding.

Grading and sorting was conducted on a B.E.I. packing line having an air blower, a tilt belt, a fruit sizing attachment, and a 10-foot grading table. This equipment was also provided by Blueberry Equipment, Inc.

For each of the experiments, five clam shells (ca. 1 pint samples) of fruit for each treatment were taken back to the Griffin Experiment Station for fruit firmness testing. Fruit firmness was measured with a FirmTech II firmness tester. The apparatus measures firmness of 25 fruit during one sampling interval. The maximum force setting for the measurements was 150 g/mm as suggested by Timm et al. (1996). Fruit firmness was tested on three 25-berry samples for each of the clam shells in each treatment before and after storage. The initial measurement was made 18 to 24 hours after harvest. After that measurement, fruit were stored for 10 to 14 days in a homeowner-style refrigerator at a temperature of approximately 40 to 42 degrees F. Fruit for the post-storage firmness measurements were allowed to achieve room temperature before firmness measurement. A total of 375 fruit were measured for firmness for each treatment at each sampling time.

Results

Fruit firmness data from Experiment 1 are presented in Table 1. The data clearly show that harvesting and handling procedures greatly influence fruit firmness. The firmest 'Brightwell' fruit were those that were hand-harvested directly into clam shells and were immediately cooled down. The firmness of these fruit was still 94 percent of its pre-storage value after 10 days of refrigeration. The softest fruit were those that were machine harvested and graded. The fruit firmness value of this treatment was only 60 percent of that of the hand-harvested, cooled immediately treatment. However, the machine harvested fruit firmness value was still 85 percent of the pre-storage value after 10 days of refrigeration. Also, the average firmness for the machine harvested fruit was well above the value of 60 to 70 g/mm of firmness reported to be an "unacceptable" level of firmness for fresh fruit (Armstrong et al., 1995; Brown et al., 1996; Timm et al., 1996). Grading and sorting of fruit reduced pre-storage firmness of fruit by 10 percent overall, and about the same reduction in firmness remained for the graded treatments overall after 10 days of cold storage. Hand harvested fruit that were graded and sorted showed a pre-storage firmness reduction of 16 percent to 29 percent as compared to hand-harvested fruit that were not graded. Grading and sorting did not decrease firmness of machine harvesting much more than the harvesting process alone. Machine harvested fruit overall showed a 22 percent decrease in pre-storage firmness as compared to hand-harvesting overall. This firmness difference in hand and machine harvested fruit is much less for the rabbiteye cultivar 'Brightwell' than has been reported for other rabbiteye cultivars (Austin and Williamson, 1977; Miller and Smittle, 1987) and some highbush cultivars (Brown et al., 1996; Mainland et al., 1975).

Fruit firmness data for treatments in Experiment 2 are listed in Table 2. The treatments that were repeated from Experiment 1 showed generally the same trend in firmness differences. Again, the hand-harvested, cooled immediately fruit were the firmest of all treatments. The data show that overall, machine harvesting of fruit caused the greatest loss of firmness (machine firmness was 22 % less than hand harvested firmness). This was followed by a 15 percent to 18 percent loss of firmness attributed to grading and sorting of fruit. Immediate cooling of fruit only caused a 8 percent increase in pre-storage firmness and a 12 percent increase in post-storage firmness as compared to keeping fruit at ambient temperature for nearly 24 hours.

The third experiment examined fruit firmness in response to harvester padding and curtains (Table 3). In general, these data indicate there was very little benefit of the curtains or pads with respect to fruit firmness. Armstrong et al. (1995) indicated padding can reduce bruising of fruit in the harvesting and handling operation. Perhaps the benefit would be more pronounced for padded grading lines or for padding in larger harvesters. The harvester model here may be too small to have severe drop heights in which berries would benefit from padding.

In summary, these experiments have shown that 'Brightwell' rabbiteye blueberry can be successfully machine harvested; however, fruit firmness is less than that for hand harvested fruit. Machine harvested 'Brightwell,' although softer than hand harvested fruit, still had an average firmness value that was acceptable after 10 to 14 days of cold storage. Grading and sorting of fruit should be considered a major contributor to fruit firmness losses. Although this process is often necessary, careful attention should be given to reducing drop heights and rough handling of fruit. This appears to be a step in the harvesting and handling operation where additional research is needed to reduce bruising. Immediate cooling of fruit did offer some increase in fruit firmness, but not to the extent expected. Although shortening the "cool down" interval after harvest will continue to be a goal of growers and packers, great benefits are not as likely to occur here as with carefully harvesting and sorting fruit.

An interesting scenario presented in these experiments is the hand-harvesting of fruit directly into clam shells in the field. This method consistently resulted in very high quality, firm fruit. Employing this method on the farm may appear to be a regression back to old methods, however, consideration should be given to this for specialty markets demanding the highest quality fruit. While harvesting by this method would slow down hand-harvesters, the total operation could be improved by circumventing the grading process in the packing shed. Hand-harvesters would have to be trained to only pick "marketable" fruit, and their daily wages would have to be the same as for hand-harvesting in bulk.

References

Armstrong, P.R., G.K. Brown, E.J. Timm. 1995. A comparison of cushioning materials for mechanical harvesting and handling of blueberries in Michigan. ASAE Paper No. 95-6173, Amer. Soc. Agri. Eng., 2950 Niles Rd., St. Joseph, MI 49085.

Austin, M.E. and R.E. Williamson. 1977. Comparison of harvest methods of rabbiteye blueberries. J. Amer. Soc. Hort. Sci. 102: 454-456.

Ballinger, W.E., L.J. Kushman, and D.D. Hamann. 1973. Factors affecting the firmness of highbush blueberries. J. Amer. Soc. Hort. Sci. 98: 583-587.

Brown, G.K., N.L. Schulte, E.J. Timm, R.M. Beaudry, D.L. Peterson, J.F. Hancock, and F. Takeda. 1996. Estimates of mechanization effects on fresh blue-berry quality. Appl. Eng. Agri. 12: 21-26.

Mainland, C.M., L.J. Kushman, and W.E. Ballinger. 1975. The effect of mechanical harvesting on yield, quality of fruit and bush damage of highbush blueberry. J. Amer. Soc. Hort. Sci. 100: 129-134.

Miller, W.R. and D.A. Smitle. 1987. Storage quality of hand- and machine-harvested rabbiteye blueberries. J. Amer. Soc. Hort. Sci. 112: 487-490.

Patten, K.D., E.W. Neuendorff, and G. Nimr. 1988. Quality of 'Tifblue' rabbiteye blueberries and efficiency of machine harvesting at different times of day. J. Amer. Soc. Hort. Sci. 113: 953-956.

Timm, E.J., G.K. Brown, P.R. Armstrong, R.M. Beaudry, and A. Shirazi. 1996. Portable instrument for measuring firmness of cherries and berries. Appl. Eng. Agri. 12: 71-77.

Response of Some Rabbiteye and Southern Highbush Blueberries to Mechanical Harvesting

D. Scott NeSmith, Stanley E. Prussia, and Gerard Krewer

Currently, about 25 percent of Georgia's commercial blueberry crop is sold as fresh fruit, with most of the remaining crop being sold for the frozen market. Much of the fresh fruit from Georgia is harvested by hand in order to maintain fruit firmness and quality. However, as hand harvesting becomes less affordable due to rising labor costs and labor shortages, many growers are interested in mechanically harvesting berries, for both frozen and fresh markets. The use of mechanical blueberry harvesters often results in much of the fruit being destined for low profit processed markets due to quality (firmness) losses. However, there is a great need for increased fresh sales of the Georgia crop.

Comparisons of machine and hand harvested fruit quality have been made for a few highbush and rabbiteye blueberry cultivars (Austin and Williamson, 1977; Ballinger et al., 1973; Brown et al., 1996; Mainland et al., 1975; Miller and Smittle, 1987; Patten et al., 1988 ). Many of these studies have shown that mechanically harvested berries are often softer than hand harvested fruit; however, mechanical harvesters have been improved in recent years to address some of the problems relating to lessened fruit quality. Also, newer cultivars better adapted to mechanical harvesting have been developed. The objective of this research was to evaluate several rabbiteye and southern highbush blueberry cultivars and selections in response to mechanical harvesting.

Materials and Methods

This experiment was conducted using mature (greater than 7 years old) blueberry plants grown at the University of Georgia's Blueberry Research Farm near Alapaha, Georgia. The plants were non-irrigated, and were in good health. Plants used for the experiment were 5 ft to 7 ft in height. Rabbiteye blueberries examined in these experiments included 'Austin,' 'Brightwell,' 'Climax,' and the selection T-256. Southern highbush blueberries used included 'Georgiagem,' and the selections TH-279 and TH-471. Each of these cultivars/selections were harvested by hand (directly into clam shell) or with a mechanical harvester. At least five bushes of each cultivar/selection were harvested.

The mechanical harvester used in this experiment was a B.E.I. model LBT (little blue tall), which was provided by Blueberry Equipment, Inc. The harvester was not self propelled, and it had a sway bar fruit detachment system. The harvester was equipped with curtains and padding. Grading and sorting of the fruit was conducted on a B.E.I. packing line having an air blower, a tilt belt, a fruit sizing attachment, and a 10 ft grading table. This equipment was also provided by Blueberry Equipment, Inc.

For fruit firmness tests of both rabbiteyes and highbush, five clam shells of fruit for hand and mechanically harvested treatments were transported to the Griffin Experiment Station's Post-Harvest Laboratory for testing. Fruit firmness was measured with a FirmTech II firmness tester. The apparatus measures firmness of 25 fruit during one sampling interval. The maximum force setting for the measurements was 150 g/mm as suggested by Timm et al. (1996). Fruit firmness was tested on three 25-berry samples for each of the clam shells in each treatment before and after storage. The initial measurement was made 18 to 24 hours after harvest. After that measurement, fruit were stored for 10 days (rabbiteye) or 21 days (southern highbush) in a homeowner-style refrigerator at a temperature of approximately 40 to 42 degrees F. Fruit for the post-storage firmness measurements were allowed to achieve room temperature before firmness measurement.

Other data taken on mechanically harvested bushes included assessment of field losses on the ground, and assessment of losses due to grading. These assessments were made for the rabbiteye blueberries only. For field loss estimates, 1 ft² areas underneath bushes were sampled after harvesting for green and ripe fruit. At least eight sampling areas were obtained for each of the cultivars/selections. Assessing losses due to grading was accomplished by taking gross weight before and net weight after grading of fruit on the above described fresh packing line. The grading line had a fruit sizing attachment with openings of 11 mm. At least two bulk replications of each cultivar/ selection were obtained from the mechanical harvesting operation.

Results

Fruit firmness data for the southern highbush are depicted in Table 1. The data indicate that the selections TH-279 and TH-471 had firmness values after mechanical harvesting equal to values for hand harvested fruit. Fruit of hand-harvested 'Georgiagem,' however, were considerably less firm than machine harvested fruit. Firmness after storage was similar for all of the highbush fruit. The storage period (21 days) was excessive, hence fruit quality deteriorated regardless of harvesting method or cultivar.

Firmness of hand harvested and machine harvested rabbiteye blueberries is shown in Table 2. All of the machine harvested fruit had less firmness than hand harvested fruit. Average firmness of fruit from both harvesting methods was well above the firmness threshold of 60 to 70 g/mm reported to be an "unacceptable" level of firmness for fresh fruit (Armstrong et al., 1995; Brown et al., 1996; Timm et al., 1996). 'Climax' is considered to be very firm fruit, and is recognized as "machinable." The new release 'Austin' displayed fruit firmness equal to 'Climax,' regardless of harvesting method. 'Brightwell' also had firmness equal to, or greater than 'Climax.' The selection T-256 had fruit firmness that was nearly equal to 'Climax.' Firmness after 10 days of storage showed a similar decline for all fruit. The post-storage firmness values were still in an acceptable firmness range however.

Table 3 presents gross yields and losses due to grading for the rabbiteye blueberries. 'Austin' had superior overall yield, and had a high degree of "pack-out." All other rabbiteye blueberries had similar gross yields per bush. 'Climax' and T-256 had a low percent pack-out. This was mostly due to small fruit size, resulting in greater losses when passing over the fruit sizing attachment. Bush condition of all selections was acceptable after machine harvesting.

Mechanical harvesting often results in significant fruit loss in the field during the harvesting operation. Table 4 indicates green and ripe berry losses (ground drops) for the rabbiteye blueberries that in response to mechanical harvesting at the first harvest. 'Austin' and 'Brightwell' both had significantly less fruit loss than did 'Climax' and T-256. In fact, ripe fruit loss was nearly double for 'Climax' and T-256 as compared to the other two cultivars. If it is assumed that a single bush covers 25 ft² (5 ft x 5 ft area), then 'Austin' and 'Brightwell' would have lost around 1 pint of berries per bush (ca. 300 berries per pint) compared to 2 pints of berries per bush for 'Climax' and T-256 following mechanical harvesting. Attempts were made to harvest all bushes at a similar ripening percentage (ca. 40% ripe fruit), however, 'Climax' and T-256 were slightly more ripe than this at the first harvest.

In summary, these results provide some useful information for growers. The data indicate that some of the selections at Alapaha, both rabbiteye and southern highbush, have the potential to be mechanically harvested with regards to fruit firmness. Mechanical harvesting can result in substantial fruit losses, and this needs to be considered when evaluating harvesting methods. The new rabbiteye release 'Austin' was well adapted to machine harvesting, especially when compared to the standard 'Climax.' T-256 generally equaled 'Climax' in response to machine harvesting. Additional tests such as these are planned for future growing seasons as long as a mechanical blueberry harvester is available for usage.

References

Armstrong, P.R., G.K. Brown, E.J. Timm. 1995. A comparison of cushioning materials for mechanical harvesting and handling of blueberries in Michigan. ASAE Paper No. 95-6173, Amer. Soc. Agri. Eng., 2950 Niles Rd., St. Joseph, MI 49085.

Austin, M.E. and R.E. Williamson. 1977. Comparison of harvest methods of rabbiteye blueberries. J. Amer. Soc. Hort. Sci. 102: 454-456.

Ballinger, W.E., L.J. Kushman, and D.D. Hamann. 1973. Factors affecting the firmness of highbush blueberries. J. Amer. Soc. Hort. Sci. 98: 583-587.

Brown, G.K., N.L. Schulte, E.J. Timm, R.M. Beaudry, D.L. Peterson, J.F. Hancock, and F. Takeda. 1996. Estimates of mechanization effects on fresh blueberry quality. Appl. Eng. Agri. 12: 21-26.

Mainland, C.M., L.J. Kushman, and W.E. Ballinger. 1975. The effect of mechanical harvesting on yield, quality of fruit and bush damage of highbush blueberry. J. Amer. Soc. Hort. Sci. 100: 129-134.

Miller, W.R. and D.A. Smitle. 1987. Storage quality of hand- and machine-harvested rabbiteye blue-berries. J. Amer. Soc. Hort. Sci. 112: 487-490.

Patten, K.D., E.W. Neuendorff, and G. Nimr. 1988. Quality of 'Tifblue' rabbiteye blueberries and efficiency of machine harvesting at different times of day. J. Amer. Soc. Hort. Sci. 113: 953-956.

Timm, E.J., G.K. Brown, P.R. Armstrong, R.M. Beaudry, and A. Shirazi. 1996. Portable instrument for measuring firmness of cherries and berries. Appl. Eng. Agri. 12: 71-77.

Use of a CPPU in Combination with Gibberellic Acid on Rabbiteye Blueberries

D. Scott NeSmith

Rabbiteye blueberry production has been on the increase throughout the southeastern United States over the past few years. There have been problems of poor fruit set due to erratic or inadequate pollination which have led to substandard fruit yields. Research efforts in Georgia over the past 8 years with the growth regulator gibberellic acid (GA₃) have overcome some of the fruit set problems with rabbiteye blueberry and have led to significant yield increases.

NeSmith and Krewer (1992) disclosed that the degree of activity of GA₃ depends on the stage of flower bud development at the time of application. It was further demonstrated that GA₃ could be used to induce fruit set of freeze damaged blueberries (NeSmith et al., 1995; NeSmith et al., 1999). Information on rabbiteye blueberry response to different rates of GA₃ has recently been reported, as has the response of several varieties to the growth regulator (NeSmith and Krewer, 1997a, 1997b, 1999). Thus, GA₃ has become widely used by growers, particularly in the southeastern United States, to increase fruit set and yield of rabbiteye blueberries which typically experience poor fruit set due to pollination problems.

Even though research has shown positive benefits from using GA₃ in many instances, there are still some problems with small, late ripening fruit when using the growth regulator (NeSmith and Krewer, 1999). According to a report by Reynolds et al. (1992), the cytokinin compound N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) has shown some positive results in increasing berry size and berry numbers per cluster in table grapes (Vitis spp.). The objective of this re-search was to examine possible enhancement of fruit size, fruit firmness, and yield of GA₃-treated rabbiteye blueberries by utilizing the growth regulator CPPU.

Materials and Methods

Five-year-old field grown blueberry plants in Griffin, Georgia, were used for this experiment. The cultivar selected was Tifblue. A split plot experiment of GA₃ and CPPU was initiated in the spring of 1999. Main plots were split into two levels of GA₃ (+ and - GA₃), and sub-plots were three CPPU treatments (no CPPU, CPPU timing 1 and CPPU timing 2). When a majority of flowers were at stage 5 to 6 of development (Spiers, 1978), applications of the growth regulator ProGibb (4% GA₃) were initiated for whole plants. The timing and rate of GA₃ were based on previous work (NeSmith and Krewer, 1992, 1997a, 1997b). GA₃ treatments consisted of one application of 200 mg/L at the appropriate growth stage, followed by a second application (same concentration)14 days later. These were applied to five rows (every other row out of 10 total rows) containing10 plants in each row. The remaining five rows were not treated with GA₃, and thus only relied on pollination for fruit set. CPPU applications were applied to three plant plots in each of the GA₃ and non-GA₃ rows. The treatments were: 1) no CPPU, 2) CPPU applied one day after the last GA₃ application, and 3) CPPU applied 14 days after the last GA₃ application. All CPPU applications were applied at a concentration of 10 mg/L. All growth regulator applications consisted of spraying whole plants to the point of drip using a back pack sprayer. All sprays utilized the nonionic surfactant X-77 at 0.25 percent. There were five replications (containing 3 plants each) of each GA₃ and CPPU combination.

Data collection from all treatments consisted of fruit number per plant, average fruit weight, fruit firmness, ripening assessment, and yield. Fruit number per plant was determined by harvesting and counting all fruit on plants. Fruit weight was determined 2 times on a 25-berry sample of ripe fruit. Ripening assessment was made by randomly stripping five shoots per bush and counting the number of green and the number of ripe fruit one week prior to first harvest (June 29, 1999). Fruit firmness was determined on a 25-berry sample per plot using a FirmTech II firmness tester. One complete harvest was made for all bushes on July 6, 1999, however, bird problems prevented continuous harvesting of fruit, so yield estimations were made. Yield estimations were made by multiplying fruit number per plant by average fruit weight. All fruit data were taken on the center bush of each three-plant plot. Thus, data bushes were bordered on each side by another bush.

Results

Ripe fruit percentage one week prior to first harvest are depicted in Table 1. The ripe fruit percentage overall was only 12 percent for GA₃-treated plants compared to 26 percent overall for plants receiving no GA₃. This response of delayed ripening has been noted previously for GA₃-treated plants (NeSmith and Krewer, 1999). The primary reason for this delay is likely the lack of seeds in the GA₃-treated plants. CPPU application timing 2 (two weeks after last GA₃ application) showed a considerable delay in ripening as compared to the other two CPPU treatments. This delay may well be due to the heavy fruit load on CPPU plants treated at timing 2 (to be discussed later).

The total number of berries per plant for the growing season and the number of ripe berries at the first harvest for all treatment combinations are presented in Table 2 and Table 3. These data show little difference in total berry number per plant between GA₃ and non-GA₃ treated plants overall. However, total berry number per plant was greatly increased for plants receiving CPPU at either timing. The second CPPU timing treatment tended to show the greatest increase in berry number per plant. These data also show that more berries were ripe for non-GA₃-treated plants than for GA₃-treated plants at the first harvest, which corresponds with previous discussions. Also, CPPU timing 2 tended to have fewer ripe berries at the first harvest. Again, this could be related to the heavy fruit load for that treatment.

Average berry weight for two sampling intervals is shown in Table 4 and Table 5. These data show a trend for GA₃-treated berries overall to be smaller than non-GA₃-treated berries. This response to GA₃ has been previously reported (NeSmith et al., 1995; NeSmith and Krewer, 1999). Average berry weight of CPPU-treated plants was greater than berries of plants receiving no CPPU. Again, CPPU timing 2 showed the greatest increase in berry weight as compared to no CPPU. Berry weight increased 10 percent to 20 percent when CPPU was applied at the second timing.

Average berry firmness at the first harvest is depicted in Table 6. These data indicate that on average, GA₃-treated fruit were 20 percent firmer than non-GA₃ fruit. This is the first observation of this to our knowledge. There was not much increase in fruit firmness with regard to CPPU treatment.

Total yield estimates made from total berry number per plant and average berry weight are listed in Table 7. These data indicate no yield differences in response to GA₃ overall. However, there was a substantial increase in yield in response to CPPU application. Yields were 2.5 to 3 times greater for CPPU treated plants than for plants receiving no CPPU. This yield increase is related to both increased berry numbers per plant and to increased berry size in response to CPPU.

Overall, these data suggest that CPPU usage can enhance yield, both with and without GA₃. The yield increase is related to both increase in fruit set and to increase in berry size. There was no yield increase resulting from GA₃ usage in this experiment. However, the use of GA₃ will continue to be beneficial in rabbiteye blueberry production in the Southeast, especially for freeze rescue. Fresh fruit varieties may not benefit from GA₃ due to the resulting reduced berry size and delayed ripening; however, the data here suggest that CPPU may overcome the small berry size problem to a degree. Berry size and maturity date are less important for processed blueberries; hence, GA₃ would likely be used to increase yields of those processed varieties.

These findings, although preliminary, strongly suggest further exploration of using CPPU in blueberry production. Experiments to better define rates and timing of the growth regulator are greatly needed. The field results showed a considerable degree of variability, but such is to be expected under field conditions with growth regulators. Carefully designed greenhouse experiments would be of benefit in further examining benefits of CPPU.

References

NeSmith, D.S. and G. Krewer. 1992. Flower bud stage and chill hours influence the activity of GA₃ applied to rabbiteye blueberry. HortScience 27: 316-318.

NeSmith, D.S. and G. Krewer. 1997a. Response of rabbiteye blueberry (Vaccinium ashei) to gibberellic acid rate. Acta Hort. 446: 337-342.

NeSmith, D.S. and G. Krewer. 1997b. Fruit set of eight rabbiteye blueberry (Vaccinium ashei Reade) cultivars in response to gibberellic acid application. Fruit Var. J. 51: 124-128.

NeSmith, D.S., and G. Krewer. 1999.Effect of bee pollination and GA₃ on fruit size and maturity of three rabbiteye blueberry cultivars with similar fruit densities. HortScience. (In press).

NeSmith, D.S., G. Krewer, and O.M. Lindstrom. 1999. Fruit set of rabbiteye blueberry (Vaccinium ashei) after subfreezing temperatures. J. Amer. Soc. Hort. Sci. 124: 337-340.

NeSmith, D.S., G. Krewer, M. Rieger, and B. Mullinix. 1995. Gibberellic acid-induced fruit set of rabbiteye blueberry following freeze and physical injury. HortScience 30: 1241-1243.

Reynolds, A.G., D.A. Wardle, C. Zurowski, and N.E. Looney. 1992. Phenylureas CPPU and thidiazuron affect yield components, fruit composition, and storage potential of four seedless grape selections. J. Amer. Soc. Hort. Sci. 117: 85-89.

Spiers, J. M. 1978. Effect of stage of bud development on cold injury in rabbiteye blueberry. J. Amer. Soc. Hort. Sci. 103: 452-455.