Downy Mildew of Cucurbit Crops
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Downy mildew (Pseudoperonospora cubensis) affects most cucurbits beginning in July or August as wind-blown spores arrive from the South. Disease 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 or blighted. 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:
- Select resistant cultivars
- Space plants for air circulation and rapid drying
- Avoid overhead irrigation
- Monitor disease using the forecasting website (www.imppipe.org)
- Apply protectant fungicides beginning when the disease is reported in nearby states; maintain a spray program for the remainder of the season.
