Devastating disease detected early this season; threatens tomatoes, potatoes in St. Lawrence County and rest of NY
Tuesday, July 10, 2018 - 2:31 pm

State Agriculture Commissioner Richard A. Ball is urging home gardeners in St. Lawrence County and around the state, greenhouse growers, and vegetable farmers to look for and report any suspicions of late blight in their tomato and potato plants and crops this summer.

Late blight is a plant disease that has the potential to cause devastation to these crops, infecting and destroying the leaves, stems, fruits, and tubers of potato and tomato plants. Photos of late blight on potatoes and tomatoes can be found at

Paul Hetzler of St. Lawrence County Cooperative Extension has written about the problem this year in his “Meandering Naturalist” column.

“Late blight is a serious plant disease that can wreak havoc on the state’s tomato and potato industry, which ranks high nationally in production,” Commissioner Ball said. “We want home gardeners, greenhouse growers and vegetable farmers to be vigilant and, at the first sign of late blight, report the finding to the Department and a local Cornell Cooperative Extension office so action can be taken as quickly as possible to prevent the spread of this extremely harmful disease.”

Late blight was detected in June several tomato plants in Onondaga County and confirmed by Cornell University’s Plant Disease Diagnostic Clinic. The plants were destroyed and inspectors will continue to monitor field plantings of tomatoes. The late blight strain detected was not one of the known or common strains.

Late blight was first discovered in the United States in the early 1840s, devastating crops across the northeast. It was also responsible for the Irish potato famine in the mid-nineteenth century.

Growers can identify late blight of potato and tomato by looking for black/brown lesions on leaves and stems. In humid conditions, visible white spores appear. As many lesions accumulate, the entire plant can be destroyed in only a few days after the first lesions are observed. The plant disease thrives in humid, wet conditions and can spread quickly from field to field, and over several miles.

Home gardeners should monitor for late blight as it can be transferred from the home garden to commercial operations. If home gardeners observe tomato plants with late blight symptoms, the Department urges them to contact their local Cornell Cooperative Extension (CCE) for assistance. It is important not to compost any diseased plant material.

Greenhouse growers should contact the Department’s Division of Plant Industry at 518-457-2087 if late blight is suspected. In addition, commercial vegetable growers should survey their tomato and potato fields for late blight and watch the blight forecast, which predicts disease incidence and directs growers to apply fungicides to protect plants. A map of current locations of late blight outbreaks can be found at The blight forecast can be found at:

If a commercial vegetable grower suspects late blight on their crops, they should work with a local CCE office or regional vegetable specialist, who can help commercial growers select the appropriate fungicide to treat the crops. Vegetable growers should employ standard late blight management procedures. Because we do not know if the strain detected is sensitive to fungicides containing mefenoxam, growers should use fungicides with other active ingredients and should be certain to rotate chemistries. Organic growers will want a product with copper.

Dr. Christine Smart, Professor of Vegetable Pathology and Director of the School of Integrative Plant Science, College of Agriculture and Life Sciences, Cornell University, said, “Cornell is working as quickly as possible to learn more about the strain of the pathogen identified here in New York. We are glad to partner with the NYS Department of Agriculture and Markets to help potato and tomato growers manage late blight.”