In 1999, US-8 clonal lineage was responsible for huge potato losses in the Red River Valley, but New York was spared any losses due to our dry conditions. Part of this planting was sprayed to kill the plants, and part is being sprayed aggressively on 5-day schedule. Scouting for Late Blight. If you are not sure that you can recognize late blight, obtain the Vegetable Crops Fact Sheet 726.20 authored by William Fry in July 1998, with colored pictures of the symptoms of late blight of potatoes and tomatoes. Scout aggressively for signs of late blight, beginning as soon as green tissue emerges.
Late blight can occur on stems as well as on leaves.
When a canopy develops, look for blight in the lower portions of the plant where the foliage stays wet. Take care not to spread late blight from field to field when scouting. Inoculum also can be carried from field to field on equipment, but is easily removed by washing with water. Early blight and Botrytis leaf blight are also occurring on potato at this time, so submitting a sample to your county agent would be appropriate for accurate identification. We can expect that most inoculum, when it occurs in the state, will be of the new immigrant genotypes which are Ridomil-resistant, and are more aggressive than the older isolates.