Downy mildew confirmed on cucumber in New Jersey

Andy Wyenandt, Rutgers Vegetable Pathologist, confirmed downy mildew on cucumber in Gloucester Co., NJ just southeast of Philadelphia today. This is the first report of cucurbit downy mildew in the Mid-Atlantic region this year. It was confirmed in an early seeded cucumber field that had been under hoops earlier in the season. Fungicides were applied today. Downy mildew is also becoming more established in the southeastern U.S. especially with the recent rainfall making it difficult for growers to scout and spray their crops.

It is important to scout your field and high tunnel crops regularly and remember that cucurbits are susceptible at any growth state. Now is the time to re-familiarize yourself with the symptoms and signs. Once present in a field, downy mildew can quickly defoliate your crop so recognizing the symptoms when scouting is important.

Cucurbit downy mildew does not overwinter in our region. Under favorable conditions the spores move both long and short distances from infected fields in the wind trajectories that pass over Pennsylvania and between individual fields. If spores are deposited from wind currents in fields when the conditions are cool and wet then downy mildew symptoms can be visible in as few as 3 to 5 days. Initially, symptoms are found on the upper surface of the leaves. The small angular spots that are delineated by the leaf veins are pale green to begin with before turning yellow in color. On the underside of the leaf, the spots look water soaked at first and under very humid conditions the lesions will sporulate giving them a purplish gray color. Keep in mind that symptoms can vary between types and varieties of cucurbits.

Please visit the Cucurbit Downy Mildew Forecasting website (http://cdm.ipmpipe.org/index.php) for the latest list of disease outbreak locations and forecasts. This information is updated by the end of the day on Monday, Wednesday and Fridays. If you suspect downy mildew on your farm, please let me know via email at bkgugino@psu.edu or by phone at 814-865-7328.