Pumpkin Downy Mildew Alert!

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Downy mildew on pumpkin and butternut squash is now present in many fields in Maryland and Delaware. Growers should scout their fields carefully. Preventative sprays are more effective than fungicides applied after the disease is established. On the lower surface the lesions are brown and angular. If viewed through a good hand lens, black flecks, which are the sporangia, may be visible. On the upper surface of the leaves the symptoms are more general and mimic many other diseases. Lesions on the upper surface appear as yellow angular spots that eventually turn brown and necrotic. Also, be aware that powdery mildew is also abundant in fields. Powdery mildew will appear as white granular spots, and is also prevalent on the leaves pictured below.

Downy mildew lesions lower surface

 Downy mildew lesions upper surface

There are several fungicides registered for managing downy mildew. The “targeted” products below should all be used in a tank mix with protectant product such as chlorothalonil or mancozeb. (These products are not effective on powdery mildew, so remember to include a product to control powdery mildew, also.)

Product (FRAC code) Efficacy on downy mildew
Presidio (43) excellent
Ranman (21) excellent
Previcur Flex (28) good (the pathogen may be developing resistance)
Tanos (11 + 27) good in alternation or tank mix
Curzate (27) good in alternation or tank mix
Gavel (22 + M3) good in alternation or tank mix


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