Do You Know How to Diagnose Cucurbit Downy Mildew in Different Cucurbit Crops?

— Written By

Cucurbit downy mildew has now been reported in Wayne, Nash, Johnston, Franklin, Sampson, Wake, Martin, Hertford, Wilson, New Hanover, Lenoir, Edgecombe, and Rowan counties.  Hosts in North Carolina reported to be infected so far include cucumber, cantaloupe, butternut squash, giant pumpkin and watermelon. All cucurbits can be severely affected by this foliar disease.

For more information about the disease and how to control it see our factsheets in english and spanish in our lab website. Control recommendations are also available in the Cucurbit downy mildew IPM pipe website, where you can also register to recieve 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.

While symptoms in cucumber are very characteristic, symptoms in other cucurbits may be harder to identify because lesions are irregular in shape instead of being angular and bound by veins, which is commonly observed in cucumber. A good way to determine if you have cucurbit downy mildew is to check the underside of the leaf for dark (brown, gray, black) sporulation with a 20X hand lens. Sporulation is typically easier to see when conditions are cool and humid, for example, early in the morning. Do not confuse cucurbit downy mildew with powdery mildew. Powdery mildew has white sporulation on the topside of the leaf. Cucurbit downy mildew has dark (brown, gray, black) sporulation on lesions on the backside of the leaf. See bellow some photos of cucurbit leaves infected with cucurbit downy mildew to help you when scouting. We also regularly post vegetable disease photos in our lab’s facebook page.

Follow us on twitter and facebook for more veggie disease alerts.

Cucurbit downy mildew symptoms in cucumber leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on cucumber leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on backside of cucumber leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on backside of cucumber leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab

Close-up of cucurbit downy mildew symptoms on cucumber leaf. Note angular lesions bound by leaf veins (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on cucumber leaf. Note angular lesions bound by leaf veins (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on backside of cucumber leaf. Note dark sporulation on some lesions (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on backside of cucumber leaf. Note dark sporulation on some lesions (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on cantaloupe leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on cantaloupe leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on backside of cantaloupe leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on backside of cantaloupe leaf. The white sporulation is not cucurbit downy mildew (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on cantaloupe leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on cantaloupe leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on backside of cantaloupe leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on backside of cantaloupe leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on watermelon leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on watermelon leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on backside of watermelon leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on backside of watermelon leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on watermelon leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on watermelon leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on backside of watermelon leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on backside of watermelon leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on gourd leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on gourd leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on backside of gourd leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on backside of gourd leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on gourd leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on gourd leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on backside of gourd leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on backside of gourd leaf. The white sporulation is not cucurbit downy mildew (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on squash leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on squash leaf. The white sporulation is not cucurbit downy mildew (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on backside of squash leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Cucurbit downy mildew symptoms on backside of squash leaf. The white sporulation is not cucurbit downy mildew (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on squash leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on squash leaf. The white sporulation is not cucurbit downy mildew (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on backside of squash leaf (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

Close-up of cucurbit downy mildew symptoms on backside of squash leaf. The white sporulation is not cucurbit downy mildew (Photo Dr. Lina Quesada, NCSU Vegetable Pathology Lab)

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
Was the information on this page helpful? Yes check No close
This page can also be accessed from: go.ncsu.edu/readext?232512