The cool, wet weather that has enveloped Pennsylvania and the Northeast this summer has created ideal conditions for a serious plant disease long feared by potato and tomato growers, according to a specialist in Penn State’s College of Agricultural Sciences.
Late blight, caused by the fungus Phytophthora infestans, can wipe out entire fields of tomatoes and potatoes within two weeks of infestation. The disease, which caused the famous Irish potato famine in the 1840s, occurs sporadically in Pennsylvania. In 1994, confirmed late blight outbreaks caused yield losses as high as 100 percent in some Pennsylvania fields, costing growers millions of dollars…
The disease thrives in cool, moist conditions. “The ideal conditions for late blight are nighttime temperatures of 50 to 60 degrees Fahrenheit — accompanied by fog, rain or heavy dew — and daytime temperatures of 60 to 70 F for at least four or five days,” says [Barbara Christ, professor of plant pathology]. “The fungus requires moisture on the leaf surface, and may die after an extended period of temperatures above 86 degrees.” …
The first symptoms are small, irregularly shaped dark spots on leaves that may expand rapidly in moist weather to form brown, blighted areas. Leaves may become limp…
Home gardeners should check their potato and tomato plants for symptoms weekly, more often during cool, wet weather. “If symptoms appear, remove and bury or burn all parts of infected plants,” says Christ…
Weather Conditions Raise Concerns about Late Blight in Crops