Cucurbit Downy Mildew Update: August 6, 2025

Continue to be on the lookout for downy mildew on cucumber and cantaloupe. It has been confirmed in Columbia, Bucks, and Lancaster counties. The closest report on watermelon and summer squash is in South Carolina. The drier weather is currently putting the region at lower risk. Now is a good time to make sure your cucumber and cantaloupe crops are protected with fungicides before the next storms are forecasted.

Preventive applications are much more effective than applications made after the disease is detected. Since fungicides are the primary management tool for downy mildew, it is important to have a well-thought-out fungicide program that rotates among different FRAC codes for fungicide resistance management, as well as tank mixes with protectant fungicides that contain chlorothalonil (FRAC M05) and mancozeb (FRAC M03) if not already in the premix. Downy mildew targeted fungicides include, but are not limited to, Orondis Opti (FRAC 49 + M05), Ranman (FRAC 21), Elumin (FRAC 22), Zampro (FRAC 40 + 45), etc. See the 2024-2025 Mid-Atlantic Commercial Vegetable Production Recommendations for a more complete list of fungicide recommendations.

Powdery mildew is also starting to show up on cucurbit crops. Remember that fungicides that specifically target downy mildew will not manage powdery mildew.

Extension educators are visiting farms and scouting for disease. If you suspect downy mildew on your farm, please contact your closest Extension educator or Leah Fronk at lxf339@psu.edu. The next report will be posted on August 13, 2025.