Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Late blight on tomato was confirmed July 7 in Maryland on tomatoes grown at Beltsville. Tomato and potato crops in Prince George’s and surrounding counties should be treated with targeted sprays for late blight. All tomato and potato crops should be scouted aggressively for signs and symptoms of late blight.
Specific recommendations for conventional tomato and potato crops can be found at the University of Delaware Commercial Recommendation Guide. http://extension.udel.edu/ag/vegetable-fruit-resources/commercial-vegetable-production-recommendations/. Fungicides such as Curzate, Forum, Presidio, Previcur Flex, Ranman, Reason, Revus Top or Tanos should be tank mixed with a protectant fungicide. Fungicides with different modes of action should be alternated.
Organic tomato and potato crops should also receive sprays for protection. In the few replicated evaluations of organic approved materials for late blight management that have been conducted, copper applied on a regular preventive schedule is the most effective. A program of copper plus Regalia alternated with copper plus Actinovate may reduce disease spread. Information on late blight for organic growers is available at: http://www.longislandhort.cornell.edu/vegpath/photos/lateblight_tomato.htm
Upper and lower surface of leaf infected with late blight. Note white sporulation on the lower leaf surface.