Effects of Fruit-Zone Leaf Removal, Training Systems, and Irrigation on the Development of Grapevine Powdery Mildew

Abstract

Removing basal leaves 2 weeks postbloom significantly reduced powdery mildew severity on clusters in each year of a study in a New York Chardonnay vineyard. In contrast, removing leaves 5 weeks postbloom had no effect. The effect was not significantly different whether one leaf or two above and below each cluster was removed. Shoot density of vertical shoot-positioned (VSP) vines was lower than that of Umbrella-Kniffen vines and was associated with a significant reduction in disease development in one year of the study. When VSP-training was combined with early leaf removal in the absence of fungicide sprays, it reduced mean disease severity by 32% relative to untreated clusters on Umbrella-Kniffen-trained vines. However, there was no effect of training system in the second year of the study. In South Australia, doubling the volume of irrigation water supplied to vines that received a standard reduced deficit irrigation program resulted in two- and seven-fold increases in foliar powdery mildew severity in two consecutive seasons. Results highlight that viticultural practices targeted primarily at controlling vine growth and crop quantity and quality can also significantly affect the development of powdery mildew.