Downy Mildew Alert for Cucumbers and Cantaloupes in PA

By Blake Jackson

Growers should remain alert for signs of downy mildew in cucumbers and cantaloupes, as confirmed cases have been reported in Columbia, Bucks, and Lancaster counties. The nearest occurrence in watermelon and summer squash has been documented in South Carolina.

Current dry conditions are keeping the region’s risk relatively low, but storms are expected soon. This is an ideal time to apply protective fungicides to cucumbers and cantaloupes before rainfall increases disease pressure.

Preventive fungicide treatments are far more effective than applications after symptoms appear. Since fungicides remain the primary control method for downy mildew, it is essential to follow a well-structured spray program.

Rotate products with different FRAC codes to prevent resistance, and include protectant fungicides such as chlorothalonil (FRAC M05) or mancozeb (FRAC M03) if they are not already part of a premix.

Commonly used downy mildew-targeted fungicides include Orondis Opti (FRAC 49 + M05), Ranman (FRAC 21), Elumin (FRAC 22), and Zampro (FRAC 40 + 45).

Powdery mildew (PM) is also starting to appear on cucurbit crops. It is important to note that fungicides for downy mildew will not control powdery mildew. PM spreads through abundant asexual spores that are easily carried by wind.

Unlike many plant diseases, dry weather favors its development and spread, while rain and surface moisture tend to slow it down. If left unmanaged, PM causes leaves to yellow and die early, leading to reduced yields and poor-quality fruit due to sunscald, diminished storage life, and weak pumpkin handles.

To manage powdery mildew, incorporate chlorothalonil into tank mixes alongside targeted products such as Vivando or DMI fungicides like Proline, Procure, Luna Experience, or Rhyme. Quintec and Torino are also effective options.

For a more detailed list of recommended fungicides, refer to the 2024-2025 Mid-Atlantic Commercial Vegetable Production Recommendations.

Extension educators are actively scouting fields and assisting with disease identification. If you suspect downy mildew on your farm, contact your local Extension educator or reach out to Leah Fronk at lxf339@psu.edu for guidance.

Photo Credit: gettyimages-diane-labombarbe