Johnson warns that late blight often develops where sprinklers overlap, and within the first 80 to 100 feet out from the center of pivot-center sprinkler systems. Potatoes should not be grown in those areas, Johnson says. Late blight can be prevented by protective fungicide sprays, which need to be applied several times during the growing season. Johnson urges potato growers to consult fieldmen and WSU county extension faculty for advice on fungicides. Control is a regional problem, Johnson says.
Cull piles are an especially important problem because they provide a place for the fungus to grow.
Late blight first appeared in Washington in 1947, near Prosser. It was next reported in the area in 1974, near Hermiston. It struck crops during seven of the next 16 years and every year since 1990. Late blight is kept in check by good management practices based on research and extension work. Johnson also has a research program aimed at development of resistant plants.