Cucumber Downy Mildew Detected in North Carolina

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Written by Lina Quesada-Ocampo and Kimberly D’Arcangelo

Cucumber Downy Mildew (CDM) was confirmed on a cucumber sample from a production field in Wilson County. Leaves displayed approximately 10% disease, but only 5% of the field was affected.

Characteristic symptoms include angular, chlorotic lesions on the upper surface of cucurbit leaves and gray sporulation on the underside of the leaves. Sporangiophore structures typical of Pseudoperonospora cubensis, causal agent of CDM, can be observed using a hand lens or under a dissecting microscope.

North Carolina growers are advised to take immediate preventative action to protect cucurbit crops. Growers are encouraged to read our Cucurbit Downy Mildew fact sheet and our annual demonstration trials for the latest fungicide recommendations. Effective fungicides can also be found in the Southeastern US Vegetable Crop Handbook. This pathogen quickly becomes resistant to fungicides and therefore it is critical to make sure fungicide groups within products are alternated and tank mixes are utilized to minimize the generation of fungicide-resistant isolates. Cucumbers and cantaloupes are generally more susceptible to the disease than squash, watermelon, and pumpkin.

Because this is an airborne pathogen that can travel from state to state, controlling CDM remains a community effort. We encourage growers and homeowners to actively and continuously scout cucurbit leaves for downy mildew and report findings of the disease to the Cucurbit Downy Mildew IPM PIPE (CDM ipmPIPE). Reports remain anonymous and are crucial in warning growers throughout the East Coast of outbreaks. No specific information needs to be provided to submit a report other than the host crop affected and the county. Also, consider registering to receive texts, emails and/or phone alerts when new disease outbreaks are reported from the CDM ipmPIPE site.

If you believe you may have CDM in your cucurbits, please contact your local Extension Agent to assist in diagnosis. Agents may also help you send a sample to the Plant Disease and Insect Clinic if a confirmation is necessary.