Growers ask: since powdery mildew is a foliar disease of a fruiting crop, is it really necessary to manage it? It may appear not to be as fruit generally are mature in the vining cucurbits when leaves die due to powdery mildew.
However, this disease causes leaves to die prematurely which in some crops can lead to fruit maturing early (cantaloupes). Winter squashes, in particular acorn, appear mature long before they are ready to harvest. Leaves need to remain healthy until fruit matures so they develop full flavor and sugar content.
When powdery mildew is not managed, melons in particular lack flavor due to low sugar content and taste bland. Winter squashes also won’t store as well and loss of protective leaves renders fruit prone to sunscald.
Pumpkin fruit color may not be as deep orange in the absence of powdery mildew control, and their handles usually are not an attractive green due to powdery mildew developing on them and they turn brown, shrivel, and cannot be used to pick up the fruit when their vine dies prematurely because of powdery mildew.
Additionally, powdery mildew can increase plant susceptibility to other diseases, notably gummy stem blight (aka black rot). Fruit production declines and ends prematurely when powdery mildew is not managed in bush type cucurbits (zucchini and summer squashes). While very rare, occasionally powdery mildew can develop directly on immature cucurbit fruit.
More information/prepared by:
Margaret Tuttle McGrath
Associate Professor
Long Island Horticultural Research and Extension Center (LIHREC)
Plant Pathology and Plant-Microbe Biology Section
School of Integrative Plant Science
College of Agriculture and Life Sciences
Cornell University
mtm3@cornell.edu