Downy Mildew Confirmed on Pumpkin in Pennsylvania

Posted: August 20, 2013

Downy mildew was confirmed on one of the most economically important vegetable crops being grown in Pennsylvania...pumpkin.
Downy mildew symptoms on pumpkin. Purple-gray sporulation is visible on the underside of the leaf.

Downy mildew symptoms on pumpkin. Purple-gray sporulation is visible on the underside of the leaf.

Cucurbit hosts confirmed with downy mildew has expanded from primarily cucumber, cantaloupe and butternut squash to now include pumpkin. Reports of downy mildew on pumpkin also are increasing in the states to our south which tend to be our source of inoculum as a result of the prevailing weather patterns. Symptoms of infections could be visible in as few as 3 to 5 days if conditions are favorable. On pumpkin, the chlorotic lesions on the upper leaf surface tend to be smaller than on cucumber but are still delineated by the leaf veins and purplish-gray sporulation will be visible on the underside of the leaves. Some bacterial diseases can look very similar so place suspect leaves in a sealed plastic bag with a dry paper towel over night and then check for sporulation the following day. Lesions caused by a bacterial pathogen will not develop sporulation under humid conditions. Suspect samples can also be submitted to the Penn State Plant Disease Clinic for diagnosis as well.

If you are currently harvesting, products labeled for cucurbit downy mildew with a 0d PHI include Ranman, Revus (poor efficacy on cucumber downy mildew), Forum, Zampro, chlorothalonil and copper (check the label for details). Previcur Flex and Presidio (poor efficacy when the pathogen originates from the southeastern U.S.) have a 2d PHI; Curzate and Tanos a 3d PHI and mancozeb and Gavel have a 5d PHI.

For the latest information on outbreaks and to receive email or text alerts please visit the Cucurbit Downy Mildew Forecasting website. If you suspect downy mildew on your farm, please let me know via email at or by phone at 814-865-7328. Updates will also be made to the 1-800-PENN-IPM hotline weekly or more frequently if needed to provide growers with information that can be used to help make timely management decisions.