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Late blight confirmed in New York, Delaware and Virginia.

Posted: June 29, 2011

Late blight is rearing its ugly head again on both tomatoes and potatoes! Continue to scout your plant vigilantly!
Symptoms of late blight on tomato (Photo: Beth K. Gugino)

Symptoms of late blight on tomato (Photo: Beth K. Gugino)

In the past couple of days two isolated cases of late blight have been confirmed on potato in Delaware and the Eastern Shore of Virginia. In Delaware, visible stem lesions were observed on two plants in a difficult to spray portion of the field. Late blight specific fungicides were going to be applied. According to Steve Rideout, Vegetable Pathologist at Virginia Tech, potato and tomato growers on the Eastern Shore of Virginia are considered at risk for late blight infection and it has been recommended that late blight specific fungicides be applied. In New York, late blight was confirmed on tomato at 3 farms and on potato at 2 farms on Long Island in an area that experiences long periods of morning fog making conditions very favorable for late blight. To-date, there have been no confirmed reports of late blight in Pennsylvania.

Late Blight Tomato

Late Blight: Phytophthora infestans

These reports serve as a reminder that scouting on a regular basis is a critical component of late blight management. When scouting for late blight, focus on higher risk portions of the field. These include shaded areas near wooded borders, lower areas of the field, and/or areas where late blight has been a problem in the past. Look for lesions that are pale green or water-soaked and gray in color on the leaves, petioles and stems. Under humid conditions, white sporulation (fuzzy growth) can develop especially on the underside of the leaves. When released, these spores can spread the pathogen to near-by plants. When dried out, the lesions appear necrotic and brown-black in color. Late blight development is favored by wet, cool weather (50-75°F), high humidity and frequent rainfall. When applied preventatively, protectant fungicides such as chlorothalonil can be used to effectively manage late blight. Incorporate late blight specific products once late blight has been confirmed in the field or nearby.

Remember that late blight is a community disease! If you suspect late blight please contact your local Penn State Cooperative Extension Office, the Penn State Plant Disease Clinic or Beth Gugino at bkgugino@psu.edu or 814-865-7328. Updates will continue to be posted on our Vegetable and Small Fruit Extension Team website (http://extension.psu.edu/vegetable-fruit) and audio-messages posted on the 1-800-PENN-IPM hotline under the tomato/potato. For the most current map of confirmed late blight outbreaks please visit http://usablight.org.