V T " c < Division of Agricultural Sciences UNIVERSITY OF CALIFORNIA PLANT REGULATORS in GRAPE PRODUCTION ROBERT J. WEAVER CALIFORNIA AGRICULTURAL EXPERIMENT STATION BULLETIN 752 PLANT REGULATORS ir T PLANT REGULATORS, now beginning to replace or augment girdling in commercial grape production, hold promise of even larger berries for Thompson Seedless and other seedless varieties. This bulletin describes experiments with two particularly promising plant regulators — 4-CPA (4-chlorophenoxyacetic acid) and BOA (benzothiazol-2- oxyacetic acid) — used on grape varieties that present special problems. Good re- sults, in all cases, depend on timing and degree of concentration, factors that vary from one locality to another. Here, in brief, are the findings: v BLACK CORINTH achieves good set and large berries with applications of 4-CPA. BOA also produces good set but smaller berries, desirable in some instances 4 THOMPSON SEEDLESS produces larger berries with firmly attached pedi- cels, is subject to less berry shatter, and may experience a slight delay in maturity when 4-CPA is applied 11 DELAYING MATURITY in Thompson Seedless, Zinfandel, and Ribier varieties with BOA depends on careful timing of the applications and use of the proper concentration 17 OTHER USES for plant regulators, such as thinning, rooting of cuttings, * and weed-killing, have been investigated with some success but are still in the experimental stage 23 THE AUTHOR: Robert J. Weaver is Lecturer in Viticulture and Associate Viticulturist in the Experiment Station, Davis. JANUARY, 1956 -* GRAPE PRODUCTION ROBERT J. WEAVER Plant regulators, long used for certain vegetable crops and tree fruits, are now entering the field of grape production. The compound 4-chlorophenoxyacetic acid (4-CPA), for example, has been found to induce a good set of large ber- ries in Black Corinth and is being used commercially to replace the girdling op- eration. (This compound is also known as para-chlorophenoxyacetic acid or PCPA.) It is also beginning to replace or supplement girdling to produce a larger berry in Thompson Seedless raised for table grapes. Another compound still in the experi- mental stage, benzothiazol-2-oxyacetic acid (BOA), markedly delays maturity in both seeded and seedless grapes. A grower may thus control rate of matura- tion, delaying the process in part of his vineyard to facilitate picking. Or he may use it to carry his grapes into later and more lucrative markets. Plant regulators such as alpha-naph- thaleneacetic acid (NAA) are also being used experimentally to thin grapes and to root cuttings. Their use for weed control in vineyards is still in the experimental stage, but the success so far achieved with 2,4-dichlorophenoxyacetic acid (2,4-D) and other compounds indicates that eventually this will be another ac- ceptable use for plant regulators. Experimental results concerning the uses in California of two of the most promising plant regulators — 4-CPA and BOA — are presented in this bulletin. * Submitted for publication February, 1955. While some of the applications discussed are now in commercial use, others are still in the experimental stages. Other possible applications have not yet yielded positive results. There can be little ques- tion that the use of still untested new compounds will yield beneficial effects. How the tests were conducted In all spray experiments, unless other- wise indicated, both the clusters and much foliage were heavily sprayed. Craftsman paint sprayers, 3-gallon pump- type sprayers, and large power sprayers have been used. Although 4-CPA is known to be com- patible with wettable sulphur, no fungi- cides or insecticides should be added to the plant-regulator solutions until more information is available. A suitable wet- ting agent was used as needed for thor- ough wetting of fruit and leaves. At harvest or sampling time the berries were removed from the clusters and thor- oughly mixed, and the weight of 100 or 200 was obtained in duplicate to deter- mine berry size. The remaining berries were crushed, and the percentage of total soluble solids in the juice was determined with a Balling hydrometer. Total acidity was determined by diluting 10 milliliters of the juice to 50 milliliters with distilled water and titrating with 0.133 N/NaOH, using phenolphthalein as an indicator. The results are expressed as grams of acid per 100 milliliters of juice, which is approximately the percentage of acid. [3] BLACK CORINTH . . . achieves good set and large berries with applications of 4-CPA. BOA also produces good set but smaller berries, desirable in some instances. The variety Black Corinth (Zante Cur- rant) , used for the currants of commerce, usually produces a very low percentage set of fruit and small berries. In some seasons almost no berries set; in others, although a fair percentage may set, the berries usually remain very small. Girdling at full bloom has been the accepted commercial method of produc- ing a good set of large berries. Since 1949 solutions of various compounds have been applied to Black Corinth clus- ters in an attempt to induce effects simi- lar to girdling (table 1) . The two regula- tors studied in these experiments — 4- chlorophenoxyacetic acid and benzothia- zol-2-oxyacetic acid — are among the most favorable. 4-CPA (4-chloro- phenoxyacetic acid) Vines sprayed with 4-CPA produced a good set of large berries (fig. 1 ) . In some locations the berries resulting from the compound were smaller than those achieved with girdling, but in most they were larger (table 2). Where larger ber- ries occurred, resulting in a heavier crop, ripening was somewhat delayed. The pedicels or capstems of treated clusters were three or four times as thick as those of clusters on girdled vines (fig. 2) ; this is neither advantageous nor disadvan- tageous. In some seasons or in regions where rotting of clusters is prevalent, more rot usually occurs on sprayed vines than on girdled, probably because the berry size of sprayed fruit is generally larger than that from girdled vines. Dur- ing the first few weeks after spraying sprayed berries grow much more rapidly than berries on girdled vines. Vines sprayed with 4-CPA usually de- velop some stunted leaves with abnormal venation, resembling those affected by 2,4-D (fig. 3). The few distorted leaves, however, do not cause any over-all de- pression of vine growth even when the compound is applied at a concentration of 20 or 40 ppm (parts per million). At Fresno a concentration of 40 ppm may result in a certain amount of injury. The formative effects on the leaves do not carry over from one season to the next, although they might if extremely hig'i concentrations were used. The clusters must be sprayed thor- oughly to achieve a good set. Experi- ments have shown that if only the foliage is sprayed, a poor set results, indicating that relatively little movement from leaves to fruit occurs. When only portions of flower clusters were treated, there was also relatively little transfer of plant reg- ulator from one part of the cluster to another (fig. 4). What is the best concentration? The optimum concentration to use varies with the location of the vineyard. A grower desiring to use plant-regulating sprays for any purpose should spray a few vines with several different concen- trations the first year to determine the best one for his particular locality. The lowest concentration that produces a maximum set of large berries is best. Higher concentrations may produce good clusters, but possibility of injury to foliage increases. At Davis the optimum concentration is from 20 to 40 ppm, while at Madera and Fresno it is probably be- tween 2% and 10 ppm (fig. 5) . This latter range applies to most of the Black Corinth-growing areas of California. [4] Compact clusters with large berries are produced both by girdling and by application of regulator. A, control; B, girdled only; C, not girdled but sprayed shortly after full bloom with 4-CPA at 40 ppm. A, girdled only. B, not girdled but sprayed shortly after full bloom with 4-CPA at 40 ppm (20 ppm produces the same effect). Berries have been removed to ex- pose the pedicels, which are three or four times thicker on the sprayed vines. Laterals on vines sprayed with 4-CPA at 40 ppm. Note stunted leaves with abnormal venation, resembling leaves from vines sprayed with 2,4-D. i B ■Fa Clusters 86 days after 4-CPA at 50 ppm was applied to (A) the apical end, (B) the apical half, (C) both apical and basal parts. The foliage was not sprayed. Note that berries have usually enlarged only where the compound was applied. When should the vineyard be treated? While higher concentrations usually result in larger berries, the time of application also has an important bearing on the results. Clusters sprayed at full bloom produce many berries that contain hard seeds, and the higher the concentration, the greater the number of such berries (tables 2 and 3). The hard seeds are usually empty. In no instance has it been possible to germinate them. Full bloom in this bulletin is consid- ered to be that time when about 70 per cent of the calyptras have fallen. At Davis, spraying should be delayed until about one week after full bloom in order to avoid the formation of hard seeds. In the warmer areas of the San Joaquin Val- ley, the interval between full bloom and spraying can be shorter. Spraying must not be delayed too long or berry shatter may begin, with a resulting loss of crop. There is usually a ten-day period during which proper spraying may be per- formed. BOA (benzothiazol- 2-oxyacetic acid) Applications of BOA produce a good set of rather small berries as compared with girdling or applications of 4-CPA (fig. 6, table 4) . Smaller berries might be of value in regions where rot is prevalent in the fruit of girdled vines or vines sprayed with 4-CPA. Small berries might also be more acceptable to the baking industry. With this compound the percentage of total soluble solids is sometimes slightly lower, and the coloration of berries is always markedly delayed. However, by harvest time the color of sprayed berries is almost as intense as that of girdled clusters. Sprayed clusters are also char- acterized by uneven ripening. When most of the cluster is fairly ripe, some small, green berries are usually interspersed among the colored ones. The optimum concentration at Davis is between 10 and 20 ppm, while in the [6] hotter regions of the state 5 or 10 ppra is enough (fig. 7). Foliage sprayed with this compound develops many characteristically cup- shaped leaves (fig. 8). The compound evidently affects the leaf margins, which are the last part of the leaf to mature. Such leaves are markedly different from those affected by 2,4-D or 4-CPA, which usually inhibit growth of leaves in width. Mixtures of BOA and 4-CPA were found in a preliminary experiment to have no advantages over the compounds used separately. Table 1. Activity of Plant Regulators Applied by Dipping or Spraying to Flowering Clusters of Black Corinth Plant regulator Benzothiazol-2-oxyacetic acid 3-Chloro-isopropyl-N-phenylcarbamate 4- Chloro-o-toloxy acetic acid 4-Chlorophenoxyacetamide 2-Chlorophenoxyacetic acid 4- Chlorophenoxy acetic acid Alpha- (2-chlorophenoxy) -propionic acid Alpha- (4-chlorophenoxy) -propionic acid N-2-chlorophenylphthalamic acid 2,4-Dichlorophenoxyacetic acid 3,4-Dichlorophenoxyacetic acid 2,4-Dichlorophenoxyacetonitrile Alpha- (2, 4-dichlorophenoxy) -propionic acid Indole-3-acetic acid Gamma- (indole-3)-n-butyric acid Beta- (3-indole) -propionic acid O-isopropyl N-phenylcarbamate Maleic hydrazide N-meta tolyl phthalamic acid Alpha-methoxyphenylacetic acid Naphthaleneacetamide Alpha-naphthaleneacetic acid Beta-naphthoxyacetic acid Alpha- (1-naphthoxy) -propionic acid Beta-naphthoxypropionic acid N-1-naphthylphthalamic acid N-phenylphthalimide Sodium salt of alpha-cyano-beta-(2,4-dichlorophenyl) acrylic acid 2,4,5-Trichlorophenoxyacetic acid 2,4,6-Trichlorophenoxybenzoic acid Alpha- (2, 4, 5-trichlorophenoxy) -propionic acid 2,3,5-Triiodobenzoic acid Concentrations tested (ppm) Activity 2.5-100 + +* 50, 500 50, 500 10-50 + + 0.5-50 0.5-50 + + 0.5-50 0.5-50 50, 500 + 0.2-200 + 0.4, 4 0.4, 4 0.2-20 2-200 20-1000 20, 200 50, 500 100, 1000 20-50 20, 50 2-200 2-200 2-200 20, 200 + 2-200 + 2-200 + 100-1000 + 10-50 + 0.5-50 20, 50 0.5-50 20, 200 + + + =Very active; percentage of set and berry size comparable with girdling. + = Active, but inferior to girdling. = Inactive, or almost inactive. * Berries rather small. [7] Table 2. Effect of 4-CPA Applied as a Spray to Black Corinth Grapes at Full Bloom at Davis and Fresno, California, in 1952 Treatment, concentration of regulator (ppm) (not girdled) 10 (not girdled) 20 (not girdled) (girdled) Weight per berry (gm) Davis 0.38 0.44 0.55 Fresno 0.18 0.57 0.60 0.37 Percentage of berries containing hard seeds Davis 10.5 18.8 1.2 Fresno 2 85 Table 3. Data at Harvest for Black Corinth Grapes from Vines Sprayed at Varying Times with 4-CPA at 25 ppm at Davis, California (Averages of four replicate canes.) Time of treatment Weight per berry (gm) Percentage of berries containing hard seeds Sprayed May 24 (full bloom) 0.48 0.35 0.36 0.37 0.32 0.18 0.37 71.8 20.9 0.1 0.8 0.4 0.3 0.0 Sprayed May 28 (stamens dried) Sprayed June 3 (berries 1/16 inch in diameter) . . . Sprayed June 7 Sprayed June 14 Not sprayed, not girdled Not sprayed, girdled Table 4. Effects on Fruit at Time of Sampling or Harvest of Applications of BOA and 4-CPA Treatment Weight per berry (gm) Degree Balling reading Percentage of acid Davis Madera Davis Madera Davis Madera Untreated control 0.15 0.47 0.18 0.35 0.36 0.20 0.41 24.3 23.7 21.5 24.5 13.4 14.0 13.8 0.84 1.10 1.09 0.89 1.05 1.48 1.15 Girdled only Benzothiazol-2-oxyacetic acid, 10 ppm 4-Chlorophenoxyacetic acid, 10 ppm [8] Black Corinth clusters from vines at Madera, sprayed shortly after full bloom with the following concentrations of 4-CPA: A, control; B, 1 ppm; C, iVi ppm; D, 10 ppm. Note that the cluster sprayed with 1 ppm has small berries and is rather straggly, but that compact clusters with large berries resulted from concentrations of 2V2 and 10 ppm. Clusters of Black Corinth at Davis 70 days after treatment with regulator: A, control; B, girdled; C, sprayed with 4-CPA at 20 ppm; D, sprayed with BOA at 20 ppm. Note that girdling and treatment with 4-CPA resulted in compact clusters with large berries, whereas the cluster treated with BOA has smaller berries and less color. [9] Y Black Corinth clusters from vines sprayed at Davis shortly after full bloom with BOA at the following concentrations: A, 5 ppm; B, 20 ppm; C, 40 ppm; D, 100 ppm. Note that ripening is rather irregular in clusters sprayed with 20 ppm, and injury becomes in- creasingly severe at 40 and 100 ppm. q Typical leaves from Black Corinth vines at Davis: A, controls; B, sprayed with 4-CPA at 40 ppm; C, sprayed with BOA at 100 ppm. Note that 4-CPA resulted in stunted growth and abnormal venation resembling that caused by 2,4-D. Foliage sprayed with BOA formed many cup-shaped leaves. Similar leaves may develop when the regulators are applied at 10 or 20 ppm. THOMPSON SEEDLESS produces larger berries with firmly attached pedicels, is subject to less berry shatter, and may experience a slight delay in maturity when 4-CPA is applied. Girdling is used commercially for table grape production in Thompson Seedless because it increases berry size. Various regulators were tested to determine whether effects similar to girdling could be induced. Of those tested, 4-CPA was found to be the best for increasing berry size (fig. 9) . The size of both girdled and ungirdled grapes was often increased about 30 to 35 per cent by sprays of regulator. Since this increase is reflected in the weight of the crop, more thinning is necessary to avoid overcropping and the development of fruit of poor quality. When a larger berry is produced, thin- ning should be more severe to prevent the development of clusters that are too com- pact. The "right" concentration The proper concentration at Davis is about 15 ppm, at Fresno 10 ppm, and in the Coachella Valley desert 5 ppm. Lower concentrations apparently suffice in hot- ter regions. In some areas the compound alone often resulted in berries as large as those produced by girdling only; in others, the sprayed berries were smaller (table 5). The greatest increase in berry size occurred in the hotter regions of the San Joaquin Valley, and the least in the cooler. Concentrations that increased berry size resulted in little injury to foliage, but higher concentrations caused much injury to the vines (fig. 10) . Table 5. The Effect of the Diethanolamine Salt of 4-CPA Applied as a Spray to Thompson Seedless Grapes Treatment, concentration of regulator (ppm) Weight per berry (gm) Percentage of total soluble solids Percentage of acid (not girdled) 5 (not girdled) 15 (not girdled) 25 (not girdled) (girdled) 15 (girdled) Stanislaus County 2.30 2.68 2.88 2.59 3.18 3.54 20.5 18.8 17.6 17.8 19.0 15.8 0.68 0.67 0.75 0.74 0.68 0.82 5 (not girdled) 15 (not girdled) 25 (not girdled) (girdled) 15 (girdled) Kern County 1.96 2.26 2.12 2.22 3.10 14.4 13.2 11.7 14.5 13.2 1.51 1.70 1.98 1.48 1.49 [11] Effect of 4-CPA at 15 ppm on berry-thinned Thompson Seedless grapes at Davis: A, control; B, sprayed; C, girdled only; D, girdled and sprayed. Note that spraying increases berry size and that the largest berries result from girdling in addition to spraying. [12] 12 Canes from g.rdled Thompson Seedless ot Sanger about four months after treatment- A control; B, sprayed with regulator at 10 ppm; C, sprayed with 4-CPA at 20 ppm. Note that the sprayed canes developed much callus and that canes are larger above the girdle than below it, especially with the 20 ppm concentration. When to spray Vines should not be sprayed before berry shatter or too many berries will set and the clusters will be too compact (fig. 13). In seeded grapes the application of 4-CPA also results in the formation of many shot berries. In an experiment at Davis, Thompson Seedless vines were sprayed with regula- tor at 15 ppm on June 10, the approxi- mate time of berry shatter, and on four later dates (table 6) . The data at harvest indicate that when the regulator was ap- plied more than a week after berry 13 Thompson Seedless: A, control; B, 89 days after treatment at flowering with 4-CPA at 50 ppm. Note many "shot" berries. [15] shatter, it had little or no effect on berry size. Many clusters from vines sprayed on June 24, July 2, and July 8 showed much splitting and callusing on peduncles, rachises and their branches, and pedicels. Berries in these lots were easily removed from the clusters, as pedicels were not firmly attached to the berries. Girdling brings about the largest in- crease in berry size when it is done soon after berry shatter. The proper time to apply regulator is, therefore, about the same as for proper girdling. Cluster or foliage spraying It is important to know whether clus- ters must be thoroughly sprayed to bring about increased berry size or whether spraying the foliage is enough. In two experiments at Davis the clusters were en- closed in paper bags to protect them from the regulator while the foliage was thoroughly sprayed. The bags were re- moved about two hours after spraying when the vines had dried. The first ex- periment was performed in 1952. At harvest, berries that had developed on the bagged clusters were larger than the untreated controls but not significantly so. Results of a similar experiment in 1954 indicated that berries became just as large if only the foliage were sprayed (table 7). Until this experiment is re- peated, however, it is recommended that the clusters be thoroughly sprayed to attain maximum berry size. Table 6. Effect of the Ammonium Salt of 4-CPA Applied as a Spray at 15 ppm to Ungirdled Thompson Seedless Vines at Davis (Averages of ten replicate canes.) Time of treatment Weight of fruit per cane (kg) Weight per berry (gm)* Percentage of total soluble solids Percentage of acid Control 16.7 19.4 15.3 14.8 17.5 14.3 2.30 2.91 2.77 2.35 2.44 2.23 21.5 20.0 19.8 19.2 18.7 19.0 0.52 0.53 0.55 0.55 0.61 0.62 June 10 June 17 June 24 July 2 July 8 * L.S.D. at 5% level, 0.85. Table 7. Influence of 4-CPA Applied to Foliage at 15 ppm on Increase in Berry Size Treatment Weight per berry (gm) 1952 2.30 2.91 2.75 1954 Control 1.79 Clusters dipped, leaves not sprayed 2.03 Clusters dipped, leaves sprayed 2.16 Clusters bagged, leaves sprayed 2.14 L.S.D. at 5% level 0.85 0.21 [16] The effect on rate of maturity To study the effect of regulator appli- cations on rate of maturation, it was necessary to eliminate the effect of crop. If regulator increases berry size by 30 to 35 per cent, the amount of crop will be increased by approximately the same amount. The larger crop tends to delay maturity. At Davis in 1953 and 1954 the number of clusters per cane was reduced on sprayed canes in an attempt to equalize the final crop on sprayed and unsprayed vines. The data indicate that the regula- tor might delay maturity somewhat. DELAYING MATURITY . . . in Thompson Seedless, Zinfandel, and Ribier vari- eties with BOA depends on careful timing of the applications and use of the proper concentration. In experiments on Black Corinth it was noted that BOA delayed coloration, sometimes depressed the percentage of total soluble solids, and resulted in the retention of a high percentage of total acid. The compound was then tested on other varieties of seedless and seeded grapes, and it was found that a marked delay in ripening occurred. Studies were conducted to determine the effect of con- centration and time of application on the rate of ripening of several grape vari- eties. Thompson Seedless In a typical experiment at Davis in 1954, canes were sprayed on June 10, the approximate time of berry shatter, with the compound at 5, 10, 20, and 40 ppm. Other canes were sprayed on July 9 when the degree Balling reading of fruit was about 6.0, and a third set of canes was treated on August 10 when the degree Balling reading was about 15. A treat- ment with the compound at 100 ppm was added in the second and third treatments. One set of canes was not sprayed. There were ten replicate canes selected at random along the rows for all treat- ments. Little injury to foliage occurred from the compound at 5 or 10 ppm, but at 20 ppm slight damage to foliage resulted from each spraying. Many leaves were characteristically cup-shaped. The injury became progressively greater with the compound at 40 and 100 ppm, much damage occuring especially on the apical one or two feet of many shoots. Fruit was harvested on September 4 (table 8). Berries on vines sprayed with the compound at 100 ppm on July 9 were markedly smaller. Many berries in this treatment remained hard and green. The higher concentrations of the compound applied at the first and second treatments resulted in significantly lower degree Balling readings and significantly higher percentages of total acid. The July 9 ap- plication resulted in the greatest retention of acidity. The August 10 treatments had relatively little effect on degree Balling reading and no significant effect on acid. Grapes sprayed soon after berry shatter developed a normal waxy bloom at ma- turity. Sprays applied on July 9 removed much of the bloom that had developed by that time, and the August 10 spraving removed most of the grapes' bloom. This situation held true with the other vari- eties tested. Similar results were obtained in an experiment near Delano (table 9). Much variation in berry size occurred after the [171 second spraying, many berries remaining small and hard (fig. 14). In all the experiments with BOA the stage of development of the fruit was closely associated with its response to the regulator. Applications made four or five weeks after normal berry shatter, when the degree Balling of fruit was about 6, usually resulted in a greater retardation than did applications made immediately after berry shatter or after the fruit at- tained a degree Balling reading of 14 or more. To determine the influence of regulator on rate of ripening, vines at Davis were trunk-girdled on June 8, 1954, after berry shatter. Regulator at a concentration of 20 ppm was applied on July 20 when the degree Balling reading was about 12.2. There were five replicate treatments of two vines each for both sprayed and un- sprayed vines. About a 10-pound sample of fruit was taken from each plot on August 24, September 8, September 23, and October 11. The spray had no effect on berry size. Sprayed fruit attained a degree Balling reading of 18 about 12 days later than that girdled but un- sprayed, and throughout ripening the degree Balling reading of sprayed fruit lagged 12 or more days behind that of the fruit girdled only (fig. 15). At the final Table 8. Data at Harvest for Girdled Thompson Seedless Grapes at Davis, California, from Canes Sprayed at Different Times with Various Concentrations of BOA (Average of ten replicate canes.) Concentration of compound (ppm) Girdled* Time of treatment Weight per berry (gm) Degree Balling reading Percentage of acid Not sprayed 2.62 21.1 0.51 Sprayed June 10 5 2.85 19.4 0.56 10 2.91 19.1 0.58 20 2.96 17.0 0.66 40 2.71 16.7 0.66 Sprayed July 9 5 1 2.66 19.6 0.67 10 2.81 17.2 0.78 20 2.48 17.1 0.79 40 2.63 16.7 0.86 100 1.84 12.1 1.15 Sprayed August 10 5 2.56 20.2 0.53 10 2.56 20.2 0.52 20 2.39 19.7 0.54 40 2.69 19.8 0.48 100 2.55 19.9 0.50 L.S.D. at 5% level between concentrations (for any given time of spraying) N.S. 0.13 0.04 L.S.D. at 5% level between times of spraying (at a given concentration) 0.14 0.79 0.04 * The vines sprayed at 100 ppm are not included in the statistical analyses. [ 18 ] sampling, however, there was a difference of only about 0.7 degree Balling between the two treatments. The difference in degree of maturity of sprayed and un- sprayed vines lessens as full maturity is approached. Throughout ripening the percentage of acid was higher in sprayed fruit. Zinfandel At Davis head-pruned vines in their fifth summer of growth, bearing 25 to 35 clusters, were used. Some vines were sprayed on June 18 about one week after berry shatter. Other vines were treated on July 19, when a few berries were begin- ning to color and the degree Balling read- ing was 4.5. A third set of vines was treated on August 28, when berries were fully colored and the degree Balling read- ing was 16.4. For each treatment the com- pound was used at concentrations of 5, 10, 20, and 40 ppm; an application at 100 ppm was added to this series in the second and third treatments. There were four replicate randomized vines for each treatment. On September 27 about 20 pounds of fruit was removed from each vine. At this time sprayed foliage showed no visible effects from the compound. The data (table 10) indicate that the July 19 Table 9. Data at Harvest (August 14) for Thompson Seedless Grapes at Delano, California, from Vines Sprayed at Different Times with Various Concentrations of BOA Time of treatment Concentration of compound (ppm) Weight per berry (gm) Degree Balling reading Percentage of acid Not sprayed 2.26 20.0 0.70 Sprayed on May 25 2 5 2.23 19.9 0.65 5 2.40 19.9 0.75 10 2.51 19.8 0.74 15 2.27 19.7 0.83 20 2.15 18.4 0.85 40 2.23 17.2 1.04 Sprayed on June 24 2 5 5 2.38 2.37 16.8 16.7 1.12 1.16 10 2.46 15.7 1.36 15 2.23 14.8 1.34 20 1.77 13.9 1.59 40 1.44 13.3 1.58 100 1.18 11.9 1.85 Sprayed on July 15 2 5 2.72 19.8 0.65 5 2.74 19.2 0.63 10 2.67 18.8 0.61 15 2.61 18.7 0.60 20 2.77 18.9 0.65 40 2.62 17.7 0.85 100 2.09 15.2 1.21 [19] 1 2l Thompson Seedless: A, control; B, 85 days after spraying with BOA at 100 ppm. Berries are small, irregular in size, and hard. 15 24 Average degree Balling readings and percentages of total acid, taken at intervals from unsprayed Thompson Seedless grapes and from grapes sprayed with BOA at 20 ppm at Davis. The L.S.D. at the 5 per cent level between means on any given date for degree Balling is 0.45 and for percentage of total acid is 0.03. For differences between dates of sampling, the L.S.D. at the 5 per cent level for degree Balling is 1.14 and for percentage of total acid, 0.10. 1.2 BALLING - Not Sprayed 16 o Sprayed ACID ■ Not Sprayed D Sprayed 24 August 8 September 23 HARVEST DATES October 1 1 1.0 .8 .6 Q < < 5 z LU u LU a. .4 spraying was the most effective in delay- ing maturation, as evidenced by the low degree Balling readings, the high per- centages of acid, and the quantity of green fruit present (fig. 16). The spray applied on August 28 had relatively little effect on rate of ripening. Ribier Cordon-pruned vines in their fifth sum- mer of growth were used. Flower clusters were reduced to about 16 per vine early in May. Sprays of BOA at concentrations of 2%, 5, 10, 20, and 40 ppm were ap- plied on July 20, when the degree Balling reading of fruit was 4.0. There were five vines per treatment. On September 16 a 40-pound sample of fruit was harvested from each treatment. On this date foliage sprayed with the compound at 2%, 5, and 10 ppm showed little or no injury. Although many leaves on the apical foot of shoots sprayed at 20 ppm were cupped, the over-all growth was not inhibited. At 40 ppm, the compound caused slightly more injury, decreasing berry size and Table 10. Data at Harvest for Zinfandel and Ribier Grapes at Davis, California, Sprayed on Various Dates with BOA Time of treatment Concentration of compound (ppm) Weight per berry (gm) Degree Balling reading Percentage of acid Percentage of surface of fruit remaining green Zinfandel Not sprayed 2.07 20.0 0.69 0.0 Sprayed June 18 . . 5 2.21 17.9 0.73 0.0 10 2.36 17.2 0.69 0.1 25 2.07 14.8 0.84 2.0* 50 2.02 14.4 0.93 10.0* Sprayed July 19. . . 5 2.03 16.8 0.78 0.0* 10 1.96 14.6 0.94 20.0* 25 1.94 14.4 1.02 25.0* 50 1.91 14.4 1.08 40.0* Sprayed August 28 5 2.08 20.6 0.68 0.0 10 2.09 17.3 0.72 0.0 25 2.15 18.0 0.72 0.0 50 2.11 19.5 0.69 0.0 Ribier Not sprayed 5.93 16.3 0.57 0.0 Sprayed July 20. . . 2.5 5.60 15.2 0.58 2.0 5 5.45 14.8 0.59 5.0 10 2.18 14.2 0.68 5.0 20 5.37 13.3 0.77 10.0 40 3.96 13.2 0.87 40.0 * Colored berries have reddish cast instead of normal blue color. [21] 16 Clusters of Zinfandel sprayed at Davis with BOA at 50 ppm on the following dates: A, control; B, June 18; C, July 19; D, August 28. Note that the July 19 spraying resulted in the most berries remaining green. 17 Clusters of Ribier 36 days after applications of BOA at 50 ppm: A, control; B, apical third treated; C, basal third treated; D, apical and basal thirds treated; E, middle third [22] degree Balling reading, retarding colora- tion, and increasing percentage of acid (table 10). At the lower concentrations maturity was only slightly delayed. In all cases some irregularity in berry size re- sulted. An experiment was designed to deter- mine whether compound applied to part of the surface of a cluster moves to other berries and there retards ripening. Apical portions of clusters were dipped and other portions painted with the com- pound at 50 ppm on July 21, when ber- ries were still green and hard. The treat- ments were: 1) control; 2) apical third of cluster dipped; 3) basal third painted; 4) middle third painted; and 5) basal third painted and apical third dipped. Observations made on August 26 showed that, on the whole, only treated portions remained uncolored, indicating little or no movement of compound within the cluster (fig. 17). OTHER USES... for plant regulators, such as thinning, rooting of cut- tings, and weed-killing, are still in the experimental stage. Chemical thinning grapes are hand-thinned, as the process Since hand-thinning is a very expen- is too expensive for wine grapes. A sive operation, the development of a method of spray-thinning might make means of thinning by chemical sprays is feasible longer pruning and the produc- highly desirable. At present, only table tion of more shoots and foliage which treated. Note that coloration was delayed only in the treated portions whether application was made by painting or dipping. [23] could nourish a larger crop. Thinning sprays might be useful to kill or injure some flowers or berries in compact clus- ters, such as Zinfandel, and to reduce the yield of overcropped vines. Thinning grapes with sprays presents certain difficulties not encountered in thinning tree fruits. The flower clusters of Vitis vinifera grapes are very small until the shoots are 3 or 4 inches long. Hand-thinning cannot be properly done until the shoots are 5 or 6 inches long. Furthermore, in California flowering does not occur until about six weeks after shoot growth has begun. Therefore, by the time the clusters are large enough to be individually sprayed, they are ob- scured by foliage that is also subject to injury. The flowers and berries of the grape are so close together on the clusters that it is very difficult to kill only a por- tion of either. Seventeen regulators, defoliants, or thinning agents, each at three or four concentrations, were applied to grapes of Vitis vinifera. Solutions of sodium mono- chloroacetate, sodium dinitro-ortho- cresylate, ammonium dinitro-ortho-sec- butylphenate, sodium dinitro-o-cyclo- hexylphenate, and alpha-naphthaleneace- tic acid, when applied at the proper con- centrations, resulted in much injury to clusters but relatively little to foliage. Cordon-pruned vines of Ribier were successfully thinned with sprays of sodium mono-chloroacetate at 0.5 per cent when the shoots averaged about 20 inches long (fig. 18). The advantages of spray-thinning clusters of cordon vines of table grapes are doubtful when hand operations such as suckering and trim- ming clusters are also needed. Flower-cluster or cluster thinning of head-pruned vines was also accomplished by killing groups of clusters. However, the distribution of the remaining clusters was poorer than after hand-thinning. This might introduce problems in prun- ing, for example, and in the maturation of fruit. Individual clusters of Zinfandel spray- ed at full bloom with alpha-naphthalene- acetic acid were often appropriately thinned (fig. 19) . Some berries remained very small as a result of the spray, thus making the compact Zinfandel less com- pact and less subject to rot. It is easy to over- or underthin. One possible use of plant regulators is to remove the second crop on vines. By the time the second-crop flowers are blooming, the first crop has developed into small berries. At this time concentra- tions of alpha-naphthaleneacetic acid that would arrest growth or kill the second- crop clusters would have little or no effect on the first-crop clusters. Thinning by chemical sprays is still in the experimental stage, and no recom- 18 Shoots of Ribier at the proper stage for spray-thinning. Clusters are readily visible but are several inches below suc- culent shoot tips. [24] mendations can be made until further work is done. Rooting of cuttings Grape cuttings treated with various plant regulators have produced a profuse growth of roots as compared with con- trols. Up to the present time, however, cuttings treated with regulator have not given a higher percentage of take in the nursery than have untreated cuttings. Relatively little work has been done on this line of investigation in California. Herbicidal uses The most troublesome weed in the coast counties is wild morning-glory, which is easily killed by 2,4-D and related compounds. Unfortunately, the grapevine is extremely sensitive to 2,4-D, and even small applications (one millionth of a gram) will affect leaf formation. Some growers, however, have applied 2,4-D successfully by using low-pressure sprays under a hooded low boom to prevent drift of spray. Others have used wet burlap soaked in 2,4-D solution to make spot applications. Either the commercial amine or the emulsive acid formulations of 2,4-D should be used, since these do not present a hazard from the standpoint of volatility. On hot soil the low-volatile esters are sufficiently volatile to cause some injury to grapes. Studies should be conducted to find compounds toxic to weeds that are relatively nontoxic to grapevines. Grasses (especially Johnsongrass and 1Q Typical clusters of Zinfandel at Davis 119 days after spraying with alpha-naphthalene- acetic acid at: A, control; B, 100 ppm; C, 500 ppm. The compound at 100 ppm gave about the appropriate degree of thinning, but that 500 ppm resulted in overthinning. In the following year a concentration much lower than 100 ppm was optimum for thinning. [25] Bermudagrass) are among the most troublesome weeds in the interior valley. Controlling grassy weeds is difficult. Dalapon shows real promise of being effective. The injurious effect of the presence of some deformed leaves on the vine is un- known at the present time. If the leaf sur- face is reduced substantially, it could be assumed that the vine is depressed. Herbicidal regulators might also be used to kill vines. When regulators, or mixtures of these compounds with inor- ganic compounds, are applied as sprays to foliage or as liquids to cuts in the bark of the vine, the whole vine, including the roots, dies rapidly. No recommendations can be made at the present time, however. ACKNOWLEDGMENTS The author is indebted to Dr. A. J. Winkler and to the late Dr. W. 0. Williams of the Department of Viticulture for their cooperation in much of this work. Mr. Stanley McCune and Mr. Donald Neuterman rendered much assistance during the course of the experimentation. The following Farm Advisors cooperated in experiments car- ried on in their respective counties: P. P. Baranek (Madera), C. V. Carlson (Mer- ced), J. R. Fleming (Fresno), D. D. Halsey (Riverside), F. L. Jensen (Tulare), A. N. Kasimatis (Kern), and G. F. Mitchell (San Joaquin). C. H. Beeman, R. A. Break, and B. S. Gould, former Farm Advisors, also cooperated in this work. REFERENCES Weaver, R. J., and W. 0. Williams 1950. Response of flowers of Black Corinth and fruit of Thompson Seedless grapes to applica- tions of plant growth-regulators. Bot. Gaz.ll :477-485. 1951. Response of certain varieties of grapes to plant growth-regulators. Bot. Gaz. 113:75-85. Weaver, R. J., and A. J. Winkler 1952. Increasing the size of Thompson Seedless grapes by means of 4-chlorophenoxyacetic acid, berry thinning and girdling. Plant Physiol. 27:626-630. Weaver, R. J. 1952. Response of Black Corinth grapes to applications of 4-chlorophenoxyacetic acid. Bot Gaz. 114:107-113. 1953. Further studies on effects of 4-chlorophenoxyacetic acid on development of Thompson Seedless and Black Corinth grapes. Proc. Amer. Soc. Hort. Sci. 61:135-143. 1954a. Effect of benzothiazol-2-oxyacetic acid on development of Black Corinth grapes. Bot. Gaz. 115:365-371. 19546. Preliminary report on thinning grapes with chemical sprays. Proc. Amer. Soc. Hort. Sci. 63:194-200. 1954c. Effect of benzothiazol-2-oxyacetic acid in delaying maturity of grapes. Science 119:287- 288. 1955. Use of benzothiazol-2-oxy acetic acid to delay maturity of grapes. Bot. Gaz. (In press.) [26] In order that the information in our publications may be more intelligible it is sometimes necessary to use trade names of products or equipment rather than complicated descriptive or chemical iden- tifications. In so doing it is unavoidable in some cases that similar products which are on the market under other trade names may not be cited. No endorsement of named products is intended nor is criticism implied of similar products which are not mentioned. 10m-l,'56(B2560)BEB GRAPE GROWING WINE MAKING TO TRAINED MEN Nearly all the grapes . . . nearly all the wines . . . ALL of the raisins produced and consumed in this country come from California. The grape and wine in- dustries of the state are giants— and still growing. Men with proper training find a variety of rewarding and interesting careers to choose from: as vineyard managers, owner-operators, winery managers, sup- pliers for vineyards and wineries, farm advisors, nurserymen, industrial field men . . . or interesting work in grape and fruit marketing, chemical spraying and dusting, food processing plants, fruit inspection, research for industry or public institutions, and teaching. Training at the University of California at Davis is ideal preparation for any of these careers. Davis has the most complete collection of grape varieties and species in the world . . . America's best library of foreign and domestic literature on grapes, wines, and brandies . . . chemical and microbiological lab- oratories . . . fermentation and conditioning rooms . . . distilling equipment cellars . . . vineyards . . . greenhouses and field houses. The teaching staff at Davis is international in reputation . . . experts who know at firsthand the sciences and business of grape growing, raisin and wine making, and brandy production. Students at Davis study with the scientists who help shape the future in these fields. Some students are employed part-time in the Department, taking part in research that is vital to the future of the industry. Address questions about courses and career opportunities to the Chairman of the Department . . . Department of Viticulture and Enology COLLEGE OF AGRICULTURE University of California • Davis A