Shoot Topping and Ethephon Effects on White Riesling Grapes and Grapevines

Abstract

Canopy modification by shoot topping or ethephon application was examined with pendelbogen-trained White Riesling grapevines in the hot, humid Piedmont region of Virginia. Treatments were: control, two levels of shoot topping (10 vs. 20 leaves per shoot retained) or ethephon application to shoot tips (600 mg/L). Topping shoots to maintain 10 or 20 leaves per shoot reduced annual cane pruning weights by an average of 61% or 24%, respectively, compared with non-topped vines. The application of ethephon produced a vine size comparable to that of vines hedged to 20 leaves per shoot. Canopy insolation was least with control vines (due to shoot tops shading original canopy) and similar among other treatments. Vines topped to 20 leaves per shoot produced more fruit than did vines topped to 10 leaves per shoot. More fruit was harvested from shoot-topped vines than from control vines in two of three years. Neither wood maturity nor dormant bud survival were adversely affected by shoot topping or ethephon application. Greatest fruit soluble solids at harvest were generally observed with vines topped to 20 leaves per shoot. Shoot topping resulted in fruit with lower titratable acidity at harvest than with control vines, but fruit pH was not appreciably affected by any treatment. Fruit rot incidence and the concentrations of rot-associated metabolites (glycerol, ethanol, and acetic acid) were significantly and mutually correlated. Fruit rot and rot metabolites were greatest with control and ethephon-treated vines and were least with vines whose shoots were topped to 10 leaves. Shoot topping to 15 to 20 leaves per shoot appears appropriate with vigorous, low-trained White Riesling to maximize benefits of this remedial canopy management practice in the humid mid-Atlantic United States.