Downy Mildew on Watermelons

— Written By and last updated by Brad Thompson

Downy mildew, caused by the oomycete Pseudoperonospora cubensis, has been reported in watermelon in North Carolina. It was observed in Nash county and the field presented 5% incidence with each infected plant/leaf having 50% severity. A previous report earlier this month was on cucumber in Duplin county.

Cucurbit downy mildew affects the leaves of all commercial cucurbits (cucumber, cantaloupe, squash, watermelon, pumpkin, etc.). Growers are advised to actively scout for the disease and initiate preventative sprays in watermelon and other cucurbits due to earlier reports. 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. To prevent fungicide resistance it is critical that growers alternate products in their fungicide programs and tank-mix with a protectant with every application.

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.