Cucumber Downy Mildew Confirmed in Buncombe County, NC – July 7, 2017

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Cucurbit downy mildew was reported by an NCDA Agronomist on July 5, 2017 in an organic, commercial cucumber field in Buncombe County, North Carolina and confirmed by Inga Meadows, Extension Plant Pathologist for Vegetables in western North Carolina.

UPDATE (7-26-17): Cucumber downy mildew also has been confirmed in Henderson County.

Symptoms were typical of downy mildew, including angular chlorotic lesions on the leaves and a grayish-brown “downy” appearance on the under side of the leaves. Structures of the oomycete Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew, were identified using dissecting and compound microscopes, confirming the disease.

Downy mildew on cucumber

Downy mildew on cucumber

Growers are recommended to take immediate action to protect cucurbit crops in NC. Typically, cucumbers, melons, and watermelons are more susceptible to the disease than squash and pumpkin.

For more information about the disease and how to control it see our Cucurbit Downy Mildew fact sheet and previous alerts. Control recommendations also are available in the Cucurbit downy mildew IPM pipe website, where you can register to receive text, email and/or phone alerts when new disease outbreaks are reported.

Upon detection, growers should use intensive spray programs every 5-7 days, especially if weather conditions are conducive (wet and cool). The downy mildew pathogen can become resistant to fungicides quickly and it is important that growers alternate products in their fungicide management programs and tank mix with a protectant upon every application. This will protect the few chemistries that are still highly effective in controlling cucurbit downy mildew.

If you think you have cucurbit downy mildew in your cucurbits please contact your local Extension Agent and send photos and/or physical samples to the Plant Disease and Insect Clinic. Physical samples are strongly preferred. If cucurbit downy mildew is confirmed in your samples by an expert, please make sure a report is sent to the Cucurbit downy mildew IPM pipe website or allow permission for us to do so.

We encourage commercial growers and homeowners to be thorough in checking cucurbit leaves for downy mildew and reporting this disease to the Cucurbit downy mildew IPM pipe website. These reports are crucial to warn growers of an outbreak, and serve as valuable data for research of this pathogen, which contributes to developing disease management strategies.