Cucurbit Downy Mildew Outbreak in Southeastern North Carolina

— Written By

Written by Emma Wallace and Dr. Lina Quesada-Ocampo

Cucurbit downy mildew was reported today (June 9, 2014) in a commercial cucumber field in Duplin County, North Carolina and confirmed by the Quesada Lab at NCSU.

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

Cucumber leaf collected from Duplin County, North Carolina on June 8th, 2014, adaxial side. Note angular, chlorotic lesions. In some cases, the lesions have started to turn necrotic and merge into one large infected area. (Emma Wallace, NCSU Vegetable Pathology Lab)

Cucumber leaf collected from Duplin County, North Carolina on June 8th, 2014, adaxial side. Note angular, chlorotic lesions. In some cases, the lesions have started to turn necrotic and merge into one large infected area (Emma Wallace, NCSU Vegetable Pathology Lab)

Cucumber leaf collected from Duplin County, North Carolina on June 8th, 2014, abaxial side. Note angular, chlorotic lesions with a grayish-brown “downy” appearance (Emma Wallace, NCSU Vegetable Pathology Lab)

Cucumber leaf collected from Duplin County, North Carolina on June 8th, 2014, abaxial side. Note angular, chlorotic lesions with a grayish-brown “downy” appearance (Emma Wallace, NCSU Vegetable Pathology Lab)

Structures of Pseudoperonospora cubensis, the oomycete that causes cucurbit downy mildew. Observed at 100x using a compound microscope (Emma Wallace, NCSU Vegetable Pathology Lab)

Structures of Pseudoperonospora cubensis, the oomycete that causes cucurbit downy mildew. Observed at 100x using a compound microscope (Emma Wallace, NCSU Vegetable Pathology Lab)

The disease seems to be just starting and only 1% of the field was affected; however, individual leaves presented about 80% disease severity. Growers are recommended to take immediate action to protect cucurbit crops in NC, especially since we will experience favorable weather for disease in the next two weeks. Typically cucumbers, watermelons and melons 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, previous alerts, and results from our demonstration trials. Control recommendations are also available in the Cucurbit downy mildew IPM pipe website, where you can also register to receive text, email and/or phone alerts when new disease outbreaks are reported.

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. 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.

With the arrival of downy mildew in North Carolina this year, we encourage commercial growers and homeowners alike to be diligent 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 on the epidemiology of this pathogen, which contributes to developing disease management strategies. With your help, we can lessen the effects of downy mildew!

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Written By

Photo of Dr. Lina Quesada-OcampoDr. Lina Quesada-OcampoAssistant Professor, Plant Pathology (Cucurbits and Sweetpotato) (919) 513-3530 lina_quesada@ncsu.eduEntomology and Plant Pathology - NC State University
Updated on May 6, 2016
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