CONTROLLING CROPPING IN LOADEL CLING PEACH USING GIBBERELLIN - EFFECTS ON FLOWER DENSITY, FRUIT DISTRIBUTION, FRUIT FIRMNESS, FRUIT THINNING, AND YIELD

Whole-tree sprays of Release LC [predominantly gibberellic acid] (GA(3 )) were applied in a commercial peach [Prunus perisca (L,) Batsch,] or chard in the California Central Valley on three dates from mid-June (a bout 90 days after full bloom = 28 days before harvest) to late July ( 14 days postharvest) 1993 at 50, 75, 100, and 120 mg . liter(-1). Gibb erellin (GA) reduced the number of flowers differentiated in 1993, the reby reducing fruit density in 1994, when sprays were applied by early July 1993, Sprays in late July did not reduce flowering and fruiting density in the following year, In 1994, there were fewer fruit located on the proximal third of the shoot after GA sprays of 75, 100, and 12 0 mg . liter(-1) applied on 15 June compared to hand-thinned controls, and reduction was linear with increase in GA rate, Fruit numbers in t he middle and distal sections of shoots were reduced by all 15 June an d some 9 July GA sprays, with fewer fruit as concentration increased, However, the distribution of fruit within shoot sections, after GA tre atments during floral differentiation, expressed as a percentage of th e total number of fruit along fruiting shoots, showed even fruiting co mpared with hand thinning, Due to reduced flowering in response to GA treatments in June and early July 1993, the hand-thinning requirement was significantly reduced, with no thinning required in 1994 from 15 J une 1993 GA sprays, All sprays applied in early July resulted in 40% t o 60% fewer fruit removed during thinning than the nontreated controls , Sprays in late July were ineffective, Sprays of GA applied in mid-Ju ne at 50, 75, 100, and 120 mg . liter(-1) and sprays of 120 mg . liter (-1) applied in early July (4 days preharvest) increased the firmness of 'Loadel' cling peach (about 26% improvement in June sprays) in 1993 , The salable yield of fruit (after removal of the undersized fruit) w as the same on hand thinned and on non-hand thinned trees treated with GA on 15 June at 50 mg . liter(-1). The salable yield of fruit was in creased by GA sprays of 50 and 75 mg . liter(-1) applied on 9 July 199 3 compared to controls, There were no differences in fruit size (by we ight or diameter) among the aforementioned treatments and hand thinnin g, GA sprays of 75, 100, and 120 mg . liter(-1) applied on 15 June 199 3 tended to reduce salable yield, but fruit size increased with decrea sed yield, Based on the results obtained in 1993 and 1994, we believe that Release LC has good potential for chemically thinning peaches in California.