Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Tomato crops across Delaware and Maryland are at risk of late blight. Late blight is now in commercial and home gardens in two counties in western Maryland, and I suspect that unreported late blight is present in additional counties. In addition, our current weather is highly favorable to this disease. Preventative fungicides should be applied. For current reported locations of late blight across the Eastern U.S., see http://www.usablight.org/
We are waiting for the determination of the genotype we have in Maryland. Isolates in nearby states have all been US-23, which means that they are sensitive to mefenoxam, the active ingredient in Ridomil Gold Bravo. Additional fungicides, which are effective on late blight when used in tank mix with a protectant fungicide, are Curzate, Forum, Presidio, Previcur Flex, Ranman, Reason, Revus Top, and Tanos. See the Delaware/Maryland Commercial Vegetable Recommendations for more information (http://extension.umd.edu/mdvegetables/2014-commercial-vegetable-production-recommendations or http://extension.udel.edu/ag/vegetable-fruit-resources/commercial-vegetable-production-recommendations/).