Fruit Set and Development in Seeded Grape Varieties as Affected by Defoliation, Topping, Girdling, and Other Treatments

Abstract

1. A method for analyzing the effects of treatments on berry set and size within different seed classes was found to be useful.

2. Partial defoliation during bloom reduced set and berry size. Treating shoot tips on partially defoliated vines with maleic hydrazide delayed shoot elongation; it increased set in one experiment, but not in another.

3. Pinching and topping shoots during bloom increased set 10 to 30 percent above that of control vines in six of seven experiments. If decreased the number of seeds per berry slightly, but did not reduce the berry weight within each seed class. Prebloom and postbloom toppings did not improve set. Repeated toppings reduced berry weight slightly. All topping treatments reduced pruning weight considerably, but, in the two years of the experiments, no harmful effects were noted.

4. Girdling increased set markedly. It increased fewer-seeded berries most, causing an increase in the number of seedess berries and/or a decrease in the number of seeds per seeded berry. It increased berry weight within each seed class up to 14 percent above that of the control.

5. Urea foliage sprays did not change set. In two of five experiments it increased berry weight 7.5 percent. When superimposed on girdling treatment, urea sprays sometimes increased and sometimes decreased set compared with girdled vines.

6. The effects of shading on fruit set and size were inconclusive, but leaves on shaded vines were larger and had more chlorophyll.

7. Gibberellic acid applied during bloom, in a single experiment, reduced set.