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Downy mildew (Pseudoperonospora cubensis) occurs on most cucurbits. It first appears as pale to bright yellow spots on the upper surface of leaves in the crown area of the plant; these spots may be irregular or “blocky” in appearance. As lesions expand and the number of lesions increases, leaves become necrotic and plants will appear scorched. On the underside of leaves, lesions will be water-soaked and slightly sunken; profuse sporulation (light to dark gray or even purple in color) will be evident on lower leaf surfaces when humidity is high. 

Downy mildew on upper side of cucumber plant foliage.

(Photo: Kenny Seebold, University of Kentucky)

Downy mildew on lower side of cucumber plant foliage.

(Photo: Kenny Seebold, University of Kentucky)

Downy mildew on pumpkin.

(Photo: Kenny Seebold, University of Kentucky)

Management:

• Use resistant cultivars (primarily cucumber)
• Avoid overhead irrigation
• Plant in sunny areas with good airflow
• Apply fungicides

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