Revista de Agronom�a (LUZ): Vol 10, No. 2, 1993

Defoliaci�n Post-Cosecha en Perlette y Thompson seedless en el Desierto Californiano

Post - harvest defoliation of Perlette and Thompson seedless under desert conditions.

M. A Duarte y E.A. Mielke

Department of Viticulture and Enology University of California, Davis, CA 95616-8749

Palabras claves: Vid, Defoliaci�n, Producci�n, Desierto

Introduction: The early grape market in the United States has been dominated by growers loated in the desert area (i.e.,Coachella Valley ant Arizona deserts).

Viticulture in the desert are as is quiet different from other states. post of the time, grapevinea do not undergo normal defoliation, ant/or the rest period is ery short because of late fall growth. Grapes grown under desert conditions tend to be less fruitful than those grown under colder climates (Lider, 1979, personal communication. It has be en suggested that this lack of fruitfulness could result from the longer crowing season and shorter maturation period. Thus, the lack of rest of the metabolism of carbohydrate reserves could be the cause of the lower fruitfulness. It has also be en observed that budbreak in these desert areas tends to be delayed when warm winters are present ant suggeats a need for rest or a chilling requirement. The present work was undertaken to determine the effect of natural ant artificial vine defoliation ant the use of growth regulators on the carbohydrate reserves, rest, budbreak, ant fruitfulness of the grapevine under Arizona desert conditions.

Method: Defoliation and Growth Regulators: The present experiment was carried out at White Wing R,anch in Yuma County, Arizona. A chemical to eliminate the new vine growth called Endothal, at 100 ppm concentration, was used. Three defoliation times were used: 4, 8, ant 12 weeks after harvest. Three growth regulators were used, Gibberellic acid (GA) 1.000 ppm, DINOSEM 1000 ppm ant Thiourea (TU) 2%, which were applied at 4, 8; and 12 weeks after harvest on defoliated and non-defoliated vines. Parameters, such as pruning weights, total carbohydrates, number of clusters per vine, and sugar content, were taken to assess the effectiveness of the treatments used. This defoliation ant growth regulator egperiment was done in a commercial vineyard where the grower carried out all normal cultural practices needed on both Thompson Seedless and Perlette varieties.

Results and Conclusions: The best treatments were the 4 and 12 weeks defoliation times with no vine growth treatments after harvest. These two treatments hastened budbreak about 10 days, more than doubled fruitfulness, and hastened harvest time by about 10 days. The main conclusions from this research are: (1) hasten budbreak, and also harvest time by about 10 days (table 1) , (2) The use of growth regulators, such as TU 2%, GA 1000 ppm, and DINOSEB 1000 ppm do not have any effect on budbreak, fruitfulness or harvest time of Thompson Seedless and Perlette varietiea grown in Arizona's desert conditions. (3) Budbreak earliness, fruitfulness ant maturation seem to depend greatly upon carbohydrate level in grapevines in the Arizona desert.

Table 1. Effect of vi.ne defoliation 4, 8, and 12 weeks after harvest with control and non-control of new vi.ne growth on �Brix
                                                Treatment                                                                                                                                                       ^oBrig