Late Blight (fungus - Phytophthora infestans): Water-soaked spots enlarge rapidly and turn brown to black. Very humid conditions may produce white mold on the underside of the leaf. Under cool, wet conditions blight may attack petioles and stems, ruining a field in a few days. Blight spores can infect tubers at harvest or while in the ground. Late blight has been verified in the Winter Garden, but has not been reported on the High Plains. Some of the isolates were shown to be metalaxyl resistant. Use fungicide applications and delay harvest about 2 weeks until vines are killed by chemical treatment.
