Effect of Pruning Severity on the Growth and Fruit Production of 'Thompson Seedless' Grapevines

¹ Department of Viticulture, University of California, Davis, CA 95616.
² Department of Viticulture and Enology, University of California, Davis, CA 95616.

A study was initiated in 1970 to evaluate the effects of different levels of pruning severity on vine growth, crop production and fruit maturity.

The pruning levels of own-rooted 'Thompson Seedless' grapevines were selected from a close visual examination by three experienced pruners of a group of 160 test vines. The variation in pruning level shown by these pruners was taken as the range in pruning severity for the experiment: 9, 15, and 22 nodes per kilogram of dormant one-year-old prunings. The assigned pruning severities were maintained for the five years of the study, with the total node count per vine varying seasonally as total prunings varied.

The variability in pruning weight, as an indication of seasonal vine growth, in this block of vigorous young vines was considerable, ranging from 1.4 to 6.8 kg per vine. The variability in pruner judgment on the number of 15-node canes to retain on vines of equal size was also considerable (3 to 5 canes). The number of nodes retained on a vine in relation to its size as determined by weight of dormant prunings affected both crop load and vegetative growth in the following summer, thereby affecting the rate of maturity of the fruit harvested.