Cucurbit Downy Mildew Confirmed in Western NC, July 28, 2021

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Cucumber downy mildew (CDM) has been confirmed on cucumber plant samples from a commercial grower in Haywood County, NC. Approximately 75-100% of plants were affected. Leaves showed symptoms typical of CDM: angular, chlorotic or yellow lesions on the upper surface of the leaves with gray to black spores on the underside of the leaf.

UPDATE (Aug 3, 2021): Downy mildew has been found on cucumber and canteloupe in sentinel plots in Haywood County, NC and on a commercial farm in Henderson County.

Cucumber downy mildew

Cucumber downy mildew

Growers in western NC are advised to implement management strategies. Effective fungicides can be found in the Southeastern US Vegetable Crop Handbook. More information can be found on the cucurbit downy mildew disease fact sheet.

Underside of cucumber leaf showing downy mildew symptoms. Photo by K. Blaedow

Underside of cucumber leaf showing downy mildew symptoms. Photo by K. Blaedow

This pathogen can rapidly become resistant to fungicides so, it is important to rotate fungicide groups and use tank mixes with protectants to minimize the risk of fungicide resistance.

Cucumbers and cantaloupes are generally more susceptible to the disease than squash, watermelon, and pumpkin. Because this pathogen travels through air currents, it can spread rapidly. Therefore, it is important that growers report outbreaks so other growers in the area can implement management strategies.

You can track the spread of CDM and report outbreaks anonymously on the Cucurbit Downy Mildew IPM PIPE (CDM ipmPIPE). If you see symptoms of CDM in your cucurbits, please notify your local Extension Agent to assist in diagnosis and to help you send a sample to the Plant Disease and Insect Clinic.