Downy mildew was found on pumpkins last week in Scioto County, OH. There have also been reports of pumpkin downy mildew in Kentucky and Illinois. Downy mildew was also reported in Clark County, OH on cucumbers. Downy mildew can be quite severe on pumpkin leaves, as shown below. Look for the angular brown lesions on the leaves. We found a great deal of the fuzzy look (sporulation) of the pathogen on the underside of these leaves. Downy mildew is managed using fungicides such as Ranman plus Bravo, alternated with Zing or another downy mildew product; products should be applied weekly.
As the summer winds down and cooler weather, with heavy morning dews, becomes common, we can expect downy mildew to ramp up. Sporangia of the downy mildew pathogen move from plant to plant through the air. They do not survive well on sunny days, but can move for long distances under overcast skies. It is important to keep downy mildew to a minimum on all types of cucurbits – not only to protect yield, but to prevent spread of the disease to other fields – near and far.