Downy mildew on cucumber

Pseudoperonospora cubensis

Downy mildew causes angular, yellow to brown lesions on top of the leaves that are restricted by leaf veins. When conditions are favorable, for example early in the morning when moisture is higher, lesions observed on the underside of the leaf may be covered in dark “down”. This downy growth is masses of pathogen spores called sporangia, which can be seen in the field with a 20X hand lens. In the presence of water, sporangia can directly germinate or differentiate into swimming zoospores that infect leaves. Identification of downy mildew in cucumber can generally be done in a field setting due to the characteristic angular lesions and pathogen sporulation in the underside of the leaf. However, in crops such as watermelon and cantaloupe where lesions do not always have the characteristic angular shape, sporulation can be scarce and diagnostics can be more difficult. 

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Factsheets

• Downy Mildew, Cornell University
• Monitoring Cucurbit Downy Mildew, Michigan State University
• Managing Cucurbit Downy Mildew, Michigan State University
• Monitoreo y Manejo del Añublo Lanoso de las Cucurbitáceas, Spanish translation
• Cucurbit Downy Mildew Fact Sheets, NC State University
• Añublo lanoso en cucurbitáceas, NC State University

Diagnostic Resources

• Cucurbit Downy Mildew Forecasts – ipmPIPE
• Cucurbit downy mildew symptoms on cucumber
• Plant Disease Clinics

Disease Control Information

• The Cucurbit Downy Mildew Forecast Homepage
• Hausbeck Plant Pathology Research Lab Downy Mildew News
• Better Know a Pest: Downy Mildew of Cucurbits (video)
• Cornell Cucurbit Downy Mildew Management Guidelines
• Downy mildew on cucurbits: Early symptoms
• Downy mildew on cucurbits: Other symptoms and imitators