OSU Extension entomologist Jim Jasinski found powdery mildew on squash in Champaign county today. The find is unusual since 1) it is very early and 2) the disease was more severe on the underside than the top of the leaves. We normally advise scouting in earnest for powdery mildew at the end of June or early July. However, southern OH growers should start looking carefully for the disease in cucurbits, checking the lower side of leaves as well as the tops.
It is not necessary to apply fungicides for powdery mildew control before it has appeared in the field. However, fungicide applications should begin when the disease is first spotted, and at a very low incidence. Powdery mildew can get away from you and cause a lot of damage. See the Midwest Vegetable Production Guide for Commercial Growers, page 98 for fungicides labeled for treatment of powdery mildew. Product ratings are included on page 109.