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AgAlert! Cucurbit Downy Mildew

Take preventative measures before these foliar diseases affect your cucumber harvest

Cucurbit downy mildew (CDM) has now been found in Monongalia County, West Virginia, as well as neighboring states – Virginia, Pennsylvania, Ohio and Maryland. For the latest information, visit the CDM regional map at

Cucurbit downy mildew (CDM) is a destructive disease that can affect most members of the gourd family or Cucurbitaceae, such as cucumber, cantaloupe, pumpkin, squash, watermelon and zucchini. However, cucumbers are the worst affected cucurbit that can be completely killed in two weeks from the onset of the disease. 

Symptoms of the disease may vary slightly from species to species, but in general, it causes angular chlorotic lesions on the foliage. These lesions appear angular because they are bound by leaf veins. During humid conditions, the lower surface of the leaf is covered with a downy, pale gray to blackish mildew. 

This is the most critical time to take preventative measures against this deadly disease. Products available for preventative use are chlorothalonil (Daconil, Bravo, Echo, Fung-onil) or mancozeb (Dithane M/F/DF, Manzate, Penncozeb). Once disease is confirmed in a field or garden, products of choice should include more effective ones. An efficacy trial at a WVU research farm in 2021 indicated that fungicide products, such as Orondis, Omega, Previcur Flex or Ranman, tank-mixed with protectants mentioned above on a seven to 10 day schedule could provide excellent control of the disease.  

Cucurbit downy mildew on a leaf. Fungal sporulation on the lower leaf surface under humid conditions.

This alert impacts all West Virginia counties. West Virginia counties bordering other states should take extra precaution, but any cucurbit crop grown in any county should be scouted carefully at this time and take preventative measures.

Please send suspected samples to WVU Plant Diagnostic Clinic.

Get help from the WVU Plant Diagnostic Clinic


Mahfuz Rahman
WVU Extension Specialist
Plant Disease Specialist
Email Mahfuz

Trade or brand names used in this publication are for educational purposes only. The use of such product names does not imply endorsement by the WVU Extension Service to the exclusion of other products that may be equally suitable.