2026 Cucurbit Downy Mildew Updates
Figure 1. Symptoms and signs of downy mildew on the upper and lower leaf surfaces of cucumber. Photo: Jennie Mazzone, Penn State
Cucurbit downy mildew is a fast‑moving, destructive vine crop disease that does not overwinter in Pennsylvania and arrives annually by wind‑spread spores from the south. Penn State Extension monitors the disease each year and reports its movement so that growers can protect their crops when it approaches. Updates for the 2026 season will be posted on this webpage as the disease is detected and moves into the region. Penn State's efforts are part of the Cucurbit Downy Mildew IPM PIPE monitoring system, which tracks confirmed reports across the United States to help predict disease movement and risk nationwide. Â
There are two types of the cucurbit downy mildew pathogen: clade 1, which primarily infects watermelon, pumpkin, and squash, and clade 2, which primarily infects cucumber and cantaloupe. Cucurbit downy mildew causes pale green, yellow, or light brown spots on the upper leaf surface and signs of gray-brown to purplish sporulation on the underside of the leaf (Figure 1). Growers who suspect cucurbit downy mildew should contact their nearby Penn State Extension Educator or submit a plant sample to the Penn State Plant Disease Clinic. See our Call for Cucurbit Downy Mildew article for additional information on the disease, reporting, and monitoring efforts. Â
Cucurbit Downy Mildew Management
Use tolerant or resistant cultivars when available and begin fungicide applications preventively when the strain affecting your crop is nearby. Applications made before infection are far more effective than those made after symptoms are observed in the field. Rotate materials with different modes of action (FRAC codes) and include a protectant fungicide (e.g. chlorothalonil or mancozeb) in each spray to reduce resistance pressure and manage other diseases like anthracnose and plectosporium blight. Recommended fungicides include Orondis Opti (FRAC 49 + M05), Ranman (FRAC 21), Elumin (FRAC 22), and Zampro (FRAC 40 + 45). Refer to the 2026-27 Mid-Atlantic Commercial Vegetable Production Recommendations for a complete list of crop-specific fungicide recommendations.
The first cucurbit downy mildew update will be posted on May 27, 2026.
Please email Jennie Mazzone at jrd5407@psu.edu if you have any questions.
