Cucurbit Downy Mildew Alert - August 26, 2026

Alert: Cucurbit Downy Mildew Protective Spray Now Warranted

As some of you may have seen in the UMass Extension Vegetable Program Alert, cucurbit downy mildew (CDM) has now been reported in Pennsylvania and northern Ohio. With storms forecasted for later this week, spores could arrive in Massachusetts and New Hampshire within the week. Cucumber and watermelon growers should begin applying targeted protectant fungicides.

Downy mildew has a high likelihood of fungicide resistance, so many products historically used are no longer effective (Quadris, Revus, Forum, Ridomil). Please rotate FRAC numbers to slow the buildup of resistance in our fields and to maintain good control options. 

To prevent disease before symptoms appear, growers can apply chlorothalonil, mancozeb, or Zampro. Once symptoms appear and you are managing the disease there are two options: tank mix with a protectant (chlorothalonil or mancozeb) and one of these products: Ranman, Presdio, Pervicur. Option 2 is to apply without a protectant and use one of these products: Orondis Opti/Ultra, Omega, Gavel, and Zing!

Orondis Opti/Ultra, Ranman, and Elumin are rated as good efficacy against downy mildew, while Zampro, Tanos, Previcur Flex, Omega, and Ridomil Gold + Bravo were rated as fair efficacy based on the 2026 Southeastern US Vegetable Crop Handbook (page 229). More detailed fungicide information and options for conventional and organic commercial growers can be found in the New England Vegetable Management Guide. 

If you suspect CDM in your field or have questions, contact Liza DeGenring or your local county field specialist. Photos of suspected infections can be send to your local county field specialist or the UNH Plant Diagnostic Lab at unh.pdl@unh.edu for diagnosis.