CORNELL (US)—Late blight, the infectious disease that caused the Irish potato famine in the 1840s, is wreaking havoc with potato and tomato plants in gardens and commercial farms in the eastern United States.
“[Late blight] has never occurred this early and this widespread in the U.S.,” warns Meg McGrath, associate professor of plant pathology and plant-microbe biology at Cornell University.
One of the most visible early symptoms of the disease is brown spots (lesions) on stems, which begin small and firm, then quickly enlarge, with slightly fuzzy white fungal growth on the underside when conditions have been humid, such as in the early morning or after rain. Occasionally the border of the spot is yellow or has a water-soaked appearance. Firm, brown spots develop on tomato fruit.
McGrath urges home gardeners to act quickly to protect their plants and to ward against the plants becoming a source of spores that could infect larger commercial farms.
The best way to prevent blight, McGrath says, is for gardeners to examine plants thoroughly at least once a week, regularly spray fungicide, and be prepared to destroy plants if blight starts to become severe.
In New York, late blight has been traced to tomato plants imported to garden centers from production facilities in the South. If tomatoes were started from seed by a gardener or a farmer in the Northeast, plants are unlikely to be infected, at least initially, she says.
Late blight, which also infects petunias, is so destructive that McGrath recommends for gardeners to consider growing other vegetables, at least for this year. Even with fungicide applied every week, there is no guarantee of success, especially if rainy weather continues, she adds.
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