Cucumber Downy Mildew Reported in North Carolina

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Downy mildew, a devastating disease on cucumbers caused by the oomycete Pseudoperonospora cubensis, has been reported in North Carolina. It was observed on cucumber in Duplin (June 1, 2016) and Sampson (June 27, 2016) counties. The field had 1-5% disease incidence, with the infected plant/leaf having 35-40% disease severity.

Cucurbit downy mildew is a foliar disease that affects all commercial cucurbits (cucumber, cantaloupe, squash, watermelon, pumpkin, etc.), but is most severe on cucumbers. Growers are advised to actively scout for the disease and initiate preventative sprays in cucurbit crops immediately. The Cucurbit Downy Mildew factsheet, previous alerts, North Carolina fungicide efficacy trials, and The Southeastern US Vegetable Crop Handbook provide recommendations for chemical control options. Growers should use intensive spray programs (every 5-7 days) once disease if found in their fields, especially if weather conditions are conducive to disease (wet and cool weather). Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew, can become resistant to fungicides very quickly. It is critical that growers alternate products in their fungicide programs and tank-mix with a protectant with every application to protect the few chemistries we have that are still highly effective in controlling downy mildew.

If you think you have downy mildew in your field, please contact your local Extension agent and send photos and/or physical samples to the Plant Disease and Insect Clinic. Reporting the occurrence of cucurbit downy mildew to the CDM IPM pipe helps us protect our state’s cucurbit industry by providing them with timely disease management information.

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