EFFECT OF SUMMER PRUNING, CLUSTER THINNING, GIBBERELLIN AND FUNGICIDE APPLICATION ON BUNCH ROT DISEASE OF GRAPEVINE CV. THOMPSON SEEDLESS.

Abstract

Two field trials with 15 years old grapevines cv. Thompson Seedless (highly susceptible cultivar) were conducted at SadatCity, Menofyia governorate, Egypt. In these trials, treatments consisted of summer pruning, i.e. ( leaf removal , shoot removal , topping and the treatment with (leaf removal +shoot removal + topping) in addition to the control vines (without summer pruning) . An additional trial , compared the cluster thinning treatment with the control ( without cluster thinning).All plots were established in a split –plot design with or without fungicides or gibberellin application .The above mentioned treatments were applied during the growing season starting at full bloom till veraison stage ( the beginning of ripening ) in order to control grapevine bunch rot disease . The obtained results showed that the disease incidence and severity of bunch rot were best reduced by using any of the used gibberellin treatments compared to that of untreated vines . The greatest reduction in disease incidence and severity was occurred in the treatments with three sprays of gibberellin when the flower cluster was 10 cm3 long, Full Bloom and 6mm in berries diameter stage which summer pruning is done . In additional trial , cluster thinning also reduced disease incidence and severity in nonsprayed control compared to the nonsprayed control ( without cluster thinning). The greatest reduction in disease incidence and severity was recorded from the treatments with three sprays of the fungicide (Euparen M) at bloom, pre-close and veraison. Also, the produced fruit yield from treated vines was significantly higher during the first and the second seasons in comparison with that of untreated vines.