,- .. {.2 "c; . ...u -‘..u- ‘.\x: —.w ‘l 4; LIBRARY :3; Michigan Scam University “Ah‘ffio This is to certify that the thesis entitled THE USE OF GIBBERELLIC ACID SPRAYS IN ALTERING FLOWERING AND FRUITING OF THE SOUR CHERRY (PRUNUS CERASUS L. CV MONTMORENCY) presented by DONALD CLAUDE COSTON has been accepted towards fulfillment of the requirements for Ph .D. degree in Horticulture »;Z‘5/?mwir%é ’ Dr. A. L. Kenworthy Major professor Date June 1,4, 1976 0-7639 ‘ BINDING BY V am & sous 1‘! ‘ C. § LIBRARY _ E“glidichig:ui Stan % University ABSTRACT THE USE OF GIBBERELLIC ACID SPRAYS IN ALTERING FLOWERING AND FRUITING OF THE SOUR CHERRY (PRUNUS CERASUS L. CV MONTMORENCY) BY Donald Claude Coston Field plots were established in Michigan commercial sour cherry orchards to investigate the potential of gib- berellic acid (6A3) sprays to improve production of low vigor trees and to prevent flowering of young trees. In the first experiment GA3 was sprayed on mature sour cherry trees two weeks after full bloom. 6A3 concentrations used were 15 ppm and 30 ppm. Nonsprayed trees were used as controls. Treatments were begun in 1972. They were repeated to give the following timings: 1972 only; 1972 and 1973; 1972 and 1974; and 1972, 1973, and 1974. GA3 sprays had no effects on yield the year of application. The percentage of vegetative buds on terminal growth was increased on sprayed trees as evaluated during bloom the year after application. Yields in 1973 were decreased as a result of 1972 GA3 sprays when compared with nonsprayed trees. Yields in 1974 from trees sprayed in 1972 were greater than from nonsprayed trees. There were no dif- ferences between sprayed and nonsprayed trees for combined 1973 and 1974 yields as affected by 1972 GA sprays. 3 Donald Claude Coston There were no differences in 1975 yields among the 30 ppm timing treatments. Yields in 1975 were increased in plots which had been sprayed with 15 ppm 6A3 in 1972 and 1973 or in 1972, 1973, and 1974. These data suggested that annual applications of 15 ppm GA should result in increased yields 3 after a decrease in yield the year following the year of first application. No differences in fruit firmness or fruit removal force were found between sprayed and nonsprayed trees. In the second experiment higher concentration of GA3 were sprayed on young sour cherry trees to try to prevent flowering. In 1973 GA3 sprays were applied to 2 and 3 year- old sour cherry trees in 4 Michigan orchards two weeks after full bloom. 6A3 concentrations used were 45 ppm and 90 ppm. The percentage of flower buds on 1973 terminal growth as counted during the 1974 bloom season was greatly reduced by all 6A3 sprays when compared with terminal growth on nonsprayed trees. However, there seemed to be no affect on flowering of spurs from the GA sprays. 3 In 1974 GA was sprayed 2, 3, and 4 weeks after full 3 bloom at 25 ppm, 50 ppm, and 100 ppm in single and repeat applications on trees in 2 Michigan orchards. GA3 sprayed at 50 ppm or 100 ppm 3 weeks after bloom and again 4 weeks after bloom eliminated most flowers on both terminal growth and spurs as evaluated during the 1975 bloom. There were no differences in terminal growth, number of nodes on terminal growth, internode length, or leaf nitrogen between sprayed and nonsprayed trees. THE USE OF GIBBERELLIC ACID SPRAYS IN ALTERING FLOWERING AND FRUITING OF THE SOUR CHERRY (PRUNUS CERASUS L. CV MONTMORENCY) BY Donald Claude Coston A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1976 ACKNOWLEDGMENTS I wish to express appreciation to Dr. A. L. Kenworthy for his guidance and encouragement during the course of graduate study. I would like to thank Drs. M. J. Bukovac, D. H. Dewey, and D. E. Linvill for their help and suggestions in this work. Appreciation is due the growers - Wally Cox, John and Jerry Stanek, Art Lister, Ozzie Herkner, and Bill Harmon. Their assistance and observations were most helpful. Much appreciation is also due Lowell Silsby, Harry Ponder, and Mike Smith. As fellow graduate students their help and friendship were and are most valuable. I would like to thank my parents, Mrs. Claude Coston and the late Mr. Coston, whose examples and ideals serve as lifetime inspirations and goals. A special word of appreciation is due Debbie, whose encouragement and patience have been unceasing. ii TABLE OF CONTENTS ACKNOWLEDGMENTS . . . . . . . . . . . TABLE OF CONTENTS . . . . . . . . . . LIST OF TABLES. . . . . . . . . . . . INTRODUCTION . . . . . . . . . . . . LITERATURE REVIEW . . . . . . . . . . SECTION I: GIBBERELLIC ACID SPRAYS TO INCREASE PRODUCTION OF SOUR CHERRY TREES (PRUNUS CERASUS L. CV. MONTMORENCY) . . . . . ABSTRACT O O O O O O O O O O O 0 MATERIALS AND METHODS . . . . . . . RESULTS AND DISCUSSION . . . . . . . LITERATURE CITED . . . . . . . . . SECTION II: GIBBERELLIC ACID SPRAYS TO REDUCE FLOWERING OF YOUNG SOUR CHERRIES (PRUNUS CERASUS L. CV. MONTMORENCY) . . . . . ABSTRACT . . . . . . . . . . . . MATERIALS AND METHODS . . . . . . . RESULTS AND DISCUSSION . . . . . . . LITERATURE CITED . . . . . . . . . SUBWRY O O O O O O O O O O O O 0 REFERENCES CITED . . . . . . . . . . . iii Page ii iii iv 10 10 12 13 21 22 22 23 25 34 35 37 LIST OF TABLES Table SECTION I Effects of gibberellic acid (GA ) sprays on the percent vegetative buds on gour cherry terminal growth the year following applica- tion. 0 O O O O O O O O O O O 0 Effects of 1972 gibberellic acid (GA3) sprays on sour cherry yields in 1973 and 1974 . . . . . . . . . . . . Effects of GA3 sprays in both 1972 and 1973 on 1974 yield of sour cherry trees . . . Effects of 15 ppm GA3 sprays on 1975 yields of sour cherry trees . . . . . . . . SECTION II The effects of 1973 GA sprays on flowering of 1973 terminal growtg as counted in 1974 at locations 1, 2, and 3. . . . . . . The effects of 1973 GA sprays on flowering 1973 terminal growth ag counted in 1974 at location 4 . . . . . . . . . . . Effect of 1974 GA Sprays on percent flower buds on 1974 terminal growth as counted in 1975 at location 1. .' . . . . . . . Effect of 1974 GA Sprays on rating of spur flowering in 1975 at location 1 . . . . Effect of 1975 GA sprays on percent flower buds on 1974 terminal growth as counted in 1975 at location 2. . . . . . . . . Effect of 1974 GA sprays on rating of spur flowering in 1975 location 2 . . . . . iv of Page 14 16 17 19 26 27 29 30 31 32 INTRODUCTION A major problem in sour cherry production is declining yields as a result of low vigor. Gibberellic acid (GA3) has been found to reduce flower bud initiation on terminal growth. The first part of the work presented in this dissertation involved investigating the use of GA sprays 3 to increase the number of vegetative buds on terminal growth. The year following the GA spray, the vegetative 3 buds should develop into spurs which would bear fruit in subsequent years. Another problem of the sour cherry industry is flowering and fruiting of trees at an early age - often, the second year in the field. The second part of the work discussed here involved the use of GA3 sprays to prevent flowering of young sour cherry trees. LITERATURE REVIEW Flower buds of the sour cherry are located laterally on one-year terminal growth and on the one-year-old part of short shoots (5 cm or less) known as spurs. Generally there are two to four flowers per bud born in each corymbose inflorescence. The flower buds are pure - that is, they contain only flower parts. Likewise, leaf buds contain only vegetative parts. The terminal bud is always vegeta- tive. As a result, elongation of spurs continues each year from the terminal resulting in relatively straight spurs. Lateral vegetative buds give rise to Spurs. On trees with about 20 cm or less terminal growth, most of the buds formed laterally are flower buds (1,25). The following year these fruit. Since no new vegetative tissue is formed laterally, the year after fruiting the shoots are "blind" (barren of vegetative buds). Shoots in the range of 20 to 45 cm will have some vegetative buds in lateral positions. The longer these shoots are, the higher will be the prOportion of vegetative buds. These vegetative buds deve10p into spurs which will bear fruit for several years. As shoot growth exceeds 45 cm, most lateral buds will be vegetative. Some of these buds likely will deve10p into lateral branches; others, into spurs. 2 Flowering and fruiting are necessary for production of the current season's crop. Maintenance of vegetative growth promotes spur formation thereby maintaining or increasing the bearing surface and insuring future crOp potential. Thus a balance of vegetative growth and fruiting is desired in a mature sour cherry orchard. To maintain high yields, trees should not be allowed to become non-vegetative. Weakly vegetative trees will be made more fruitful by any treatment which increases growth without reducing fruiting surface (39). Gardner (11) proposed that the ultimate upper limit on crop size, with no frost or leaf spot, is set by factors such as soil fertility and moisture supply. He maintained that it is reasonable to encourage heavy cropping by promoting Optimum tree deve10pment. He recommended that 30 to 60 cm of terminal growth be maintained during the early years of tree life to develop a large fruiting sur- face. When trees are mature 15 to 30 cm of terminal growth will maintain yields. Similar observations were made by Kenworthy (25). Many Michigan sour cherry producers observe that plantings are decreasing in productivity as they become older. The "blind" shoots (those without spurs) mentioned previously continue to develop over several years. When this occurs the tree takes on a willowy appearance, fruit is only born laterally on the previous year's terminal growth, and the only leaves are from the terminal vegetative bud. The terminal growth is essentially performing as a spur. In addition to low production, the willowy branches are not stiff enough to allow good shaking action from mechanical harvesters. The fruit either remains on the tree or the tree is injured by excessive shaking in trying to remove the fruit. The cause oftfluablind willowy shoots is often attri- buted to a virus complex. Keitt and Clayton (21) reported that a bud transmissible disease of sour cherry existed in Wisconsin and that the causal agent was a virus. They later reported that this was a disease which formerly was called "physiological yellow leaf" and had been blamed on unfavorable soil and weather conditions (22). A further report (23) included a proposal to call the disease "cherry yellows". Work in New York confirmed these findings (18). Sour cherry yellows has now been shown to result from a complex of two viruses - necrotic ring spot and prune dwarf (6, 7). Necrotic ring spot is found without prune dwarf but prune dwarf is not found in the absence of necrotic ring spot. It is generally accepted that the tree is infected with ring spot first and is thereby predisposed to prune dwarf. Symptoms of ring spot are usually found on only a few branches the first year (20). The following year other branches show symptoms though the original area may not. In the years symptoms occur, the tree is considered in the "shock" stage. Later the trees appear normal unless yellows deve10ps. Symptoms during the “shock" stage are most pro- nounced for the two weeks following petal fall. Leaves may be small and have depressed fine etching. Partial to complete rings may deve10p. These may become necrotic and fall out giving the leaf a tattered appearance. Necrotic ring spot affects growth and production. Growth may be reduced 10 to 30% (9,34). Bud take in prOpa- gation may be reduced up to 50% when infected scion wood is used (31). There may be a reduction in growth of nursery trees (31). Yield reductions are reported from 20 to 56% (9,30,34). Yield will generally recover to about 90% of normal within one or two years providing yellows does not develop (31). Symptoms of yellows (4,15,24,26) include a striking green and yellow mottling which appears on the leaves about three to four weeks after petal fall, a much reduced spur system, and long willowy terminals. The last two suggest a set of circumstances quite akin to that described previously. In addition, there is early summer leaf drop. When the yellows complex is present there may be severe yield reductions (9,26,29,33,42). Since this is primarily the result of a reduction in the number of pro- ductive spurs, the yield reduction may occur over several years. Reduction may be greater than 50% (33). Another factor also observed is reduced fruit set resulting from pollination with infected pollen (33). Necrotic ring spot spreads slowly in orchards less than 4 or 5 years old (8). Prune dwarf generally comes in several years after ring spot and doesn't really spread rapidly until after the trees are about 10 years old (8). Perhaps the most perplexing problem with these diseases is that they are spread by pollen (12,13,14,l6,l7,4l). Becausecnfthis, it is almost impossible to keep them out of an orchard (especially if near other infected orchards). These diseases have a profound effect on the sour cherry industry. Yellows will eventually move into prac- tically all blocks. Control suggested in Michigan is aimed at retarding the movement of the viruses into cherry plantings rather than curing trees (20). Recommended practices are: purchasing virus-free trees, isolating plantings at least 100 feet (preferably 500) from existing blocks, planting solid blocks, and not replanting when a tree dies. Other practices (37) which may prove beneficial include roguing diseased trees and eliminating any factors unfavorable to tree growth. An increase in growth might be expected to improve the situation. Cain and Parker (5) reported that extra nitrogen stimulated vegetative growth in yellows-infected trees resulting in greater spur production and increased fruiting capacity. Increased yields were noted. Another approach to the problem is the use of gibberellic acid (GAB)' Hull and Klos (19) found that GA sprays seemed 3 to overcome some of the stunting effects of yellows. Others (3,10,28,35,36) have confirmed this observation. GA3 treatment results in an increase in the number of vegetative buds on the terminals. Treatment is most effec- tive if sprays are made two weeks after petal fall. The vegetative buds on the terminals act like those described previously. The year after treatment, they deve10p into spurs which fruit the next year (two years after treatment). Some will tend to grow into shoots which will also help increase fruiting surface. Yields are reduced the year following the first application, with yields increased in subsequent years (28). The treatment should be repeated every year since spurs will form only the season following treatment and a lapse in the program will deter spur for- mation (35). Concentrations in the range of 15 to 25 ppm GA3 have been found to be effective (35). Parker 35 El (35) recommended that the 6A3 concentration be adjusted so that 30 to 40% of the lateral buds on the terminals are vegetative. In New York (3,35) the addition of 2 quarts glycerin or 1 pint Tween 20 to 100 gallons of spray with 200 to 300 gallons of spray per acre was suggested. In Michigan (33) adjuvants did not seem to improve performance. Cool and bright conditions during spraying seem conducive to best results (10). On trees which have had yellows for some time, pruning back several years' growth prior to GA 3 application should prove beneficial (35) . In addition to yield increases, Parker gt_al (35) list other advantages to the GA approach for treating 3 yellows symptoms. Twigs are stronger and less flexible which should reduce wind whip injury and make mechanical harvesting easier and less damaging. Increased numbers of leaves from greater twig growth should help prevent wind damage to the fruit. In many orchards that have the "blind" willowy shoots there are no symptoms of the viruses involved in the sour cherry yellows virus complex. The condition results from low vigor. The cause may be winter injury, harvester injury, or the viruses described above. In any event, the appearance and performance of the tree are the same. Higher nitrogen applications to increase vigor should help overcome these problems (2,11,27,38,40). However, nitrogen alone may not be effective in producing the necessary increased terminal growth. Orchards with a high percentage of spur-born fruit tend to have high yields (2,11,40). Spurs bear fruit for several years. Increasing the number of spur-born fruit usually is accompanied by an increase in fruit born laterally on shoot growth (11,40). GA3 should promote spur formation on "low vigor" trees in a manner similar to that described previously for trees suffering from sour cherry yellows. This hypothesis was investigated as the first part of this dissertation. A similar problem is the flowering and fruiting of young sour cherry trees, sometimes as early as their second year in the field. This takes much of the tree's vitality and reduces terminal growth. The resulting trees are small with very little bearing surface. In many cases, they die. Use of nitrogen does not always prevent early flowering. In some of the early GA investigations with sour cherry 3 yellows, it was noted that higher concentrations resulted in an almost complete absence of flower buds on terminals (3). The second part of this dissertation investigates the possibility of using GA3 to prevent flowering on young sour cherry trees. The two parts of the dissertation are prepared in the style for research papers in the Journal of the American Society for Horticultural Science. SECTION I GIBBERELLIC ACID SPRAYS TO INCREASE PRODUCTION OF SOUR CHERRY TREES (PRUNUS CERASUS L. CV. MONTMORENCY) Abstract. Eight-year-old sour cherry trees were sprayed with 15 or 30 ppm gibberellic acid GA3 beginning in 1972. Some were resprayed to give the following timings: sprayed 1972; sprayed 1972 and 1973; sprayed 1972 and 1974; and sprayed 1972, 1973 and 1974. The year following treatment there were more vegetative buds on one-year-old wood of sprayed trees that non- sprayed trees. Yield was reduced in 1973 as a result of 1972 treatment. Yield was increased in 1974 as a result of the 1972 sprays. However, the combined 1973 and 1974 yields for sprayed trees were not greater than for nonsprayed trees. Thirty ppm treatments showed no effects on 1975 yields. Trees sprayed each year with 15 ppm had higher yields than nonsprayed trees in 1975. There were no differences in fruit firmness and fruit removal force among treatments. Flower buds of the sour cherry develop laterally on the current season's terminal growth and on spurs. The following year they flower. On bearing trees, low vigor often results in all the lateral buds on the terminal growth being floral. This generally occurs when the terminal growth is less than about 20 cm long. After the 10 11 year of bloom, the wood is barren of lateral vegetative growth. If some of the buds on terminal growth are vegetative, the following year they will develop into spurs which will bear fruit for several subsequent years. Prolonged low vigor or short terminal growth results in a willowy appearance of the tree since no spurs are. formed. Fruit will only be born on the previous year's terminal growth. No spurs or lateral branches will develop since no vegetative buds are on the previous year's ter- minal growth. Several factors may lead to such a situation. The one most often described as the cause is sour cherry yellows virus complex. This disease is caused by a complex of two viruses - necrotic ring spot and prune dwarf (3,4). Other causes of the low vigor situation may be low nutrient levels, winter injury, or summer defoliation from cherry leafspot. Several researchers (1,5,6,9,10) have used gibberellic acid (6A3) sprays to combat the effects of the sour cherry yellow virus complex. Such sprays increase the number of vegetative buds on terminals. The year following treatment these vegetative buds develop into spurs which bear fruit in the following years. The present work was initiated to determine if GA3 sprays would be effective in producing similar results in "low vigor" trees. The trees used showed necrotic ring spot symptoms the year before the first treatment. Yellows symptoms were not observed during the treatment period. MATERIALS AND METHODS The trees used were in a commercial orchard in the Traverse City, Michigan area. At the outset of the work, they were 8-years old. Gibberellic acid (GA3)l was sprayed to runoff at 15 or 30 ppm. Approximately 8 liters of dilute GA solution per 3 tree were necessary. The trees were sprayed initially in 1972. Some of the trees were resprayed in 1973 and/or 1974 to give the following timing combinations at each concn: sprayed 1972; sprayed 1972 and 1973; sprayed 1972 and 1974; and sprayed 1972, 1973, and 1974. All trees which had previously been treated, were retreated in 1975. Nonsprayed trees were used as controls. A split-plot design with 3 replications and plots of 5 trees were used. The trees were harvested mechanically and the fruit from each 5-tree plot was delivered to a water-filled standardized rectangular metal tank (2). The depth of cherries in the tank was measured with a standard probe.2 Weight of cherries in the tank was then determined by com- puting volume and coverting to kilograms (1 cm depth = 8.5kg cherries). Yield data are shown as kg per tree with mean separation by percent of control. lPro-Gibb (3.91% liquid formulation). Abbott Laboratories, North Chicago, Illinois. 2Tresco, Spring Lake, Michigan 12 13 In 1973 and 1974, the flower and vegetative buds on 5 terminal shoots produced the year of treatment (each less than 20 cm long) were counted per tree. The terminal bud which is vegetative was counted each time. Data are expressed as precent vegetative buds. Fruit firmness and fruit removal force were measured in 1974 and 1975. These data were regarded as measures of fruit maturity. Firmness was measured with a Durometer, type 001 (8). Fruit removal force was evaluated using a Hunter Mechanical Force Gauge2 equipped with a slotted claw (7). A sample of 150 fruit per S-tree plot was taken 7 days prior to harvest for each of these measurements. RESULTS AND DISCUSSION In none of the years of the experiment did GA3 sprays affect yield the year of treatment. GA3 sprays on sour cherry have been found to affect bud initiation (6) and thus should have no effect on buds formed the year before treatment. The percentage of vegetative buds on terminal growth was increased on sprayed trees when compared with non- sprayed trees (Table 1). Previous studies (l,5,6,9,10) had lShore Instrument and Mfg. Co., Jamaica, NY. 100 units represents 113.5 g resistance. 2Hunter Spring Co., Lansdale, PA 14 Table 1. Effects of gibberellic acid (GAB) sprays on the percent vegetative buds on sour cherry terminal growth the year following application.2 % Vegetative Budsy GA Concn 3 (ppm) 1973x 1974 0 (Nonsprayed) 19 a 19 a 15 36 b 60 b 30 52 b 44 b zMean separation within columns by Duncan's Multiple Range Test, 5% level. Means followed by the same letter are not significantly different. Y% Vegetative Buds = (Number of Vegetative Buds/Total Number of Buds) x 100. xThe years shown were the years counts were made during bloom. The GA was applied the previous year in each case. The terHinal growth was that produced the year of treatment. 15 similar findings. There were no differences in the total number of buds (flower + vegetative) in either year between sprayed and nonsprayed trees. Therefore, there was an increased number of vegetative buds present, each with the potential of becoming a spur. Yield data for 1973 and 1974 as affected by 1972 GA Sprays are presented in Table 2. The 1973 yields were 3 lower than 1974 because of cool weather during the 1973 bloom period which hindered bee movement, pollination, and fertilization. The 1973 yields for trees sprayed in 1972 was less than for nonsprayed trees. There were fewer flower buds on the terminals of the Sprayed trees in 1973 and thus the yield was less since there were few spurs on these trees. In 1974 there was an increase in yield from trees sprayed in 1972 (Table 2). It was assumed that the vegeta- tive buds formed in 1972 as a result of the GA3 spray develOped into spurs in 1973 and were bearing fruit in 1974. There were no differences in combined 1973 and 1974 yields between Sprayed and nonsprayed trees (Table 2). The increase in yield in 1974 was approximately equal the decrease in yield in 1973 for trees sprayed in 1972. Yield in 1974 was increased on trees sprayed in both 1972 and 1973 with 15 ppm GA (Table 3). 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