Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Early blight is one of the most common tomato diseases in the U.S. It occurs yearly in our region, but is most severe in periods of moderate temperatures and high leaf wetness. Early blight lesions may form on leaves, stems or fruit, and the lower (older) leaves are affected first. The lesions on leaves are dark with distinct concentric rings. They may be small, but can range up to ½ inch or more in diameter. Infected leaves may turn chlorotic. Early blight has become problematic this year because of our cool weather and high humidity. Many fungicides are available to manage early blight. Alternate a broad spectrum fungicide such as chlorothalonil, mancozeb, or Gavel with a more targeted material. Targeted fungicides include Cabrio, Endura, Flint, Fontelis, Priaxor, Quadris, Quadris Top, Revus Top, and Tanos. Remember to always alternate materials in different FRAC codes. Organic growers may find some benefit from use of OMRI approved copper products, or Sonata. All growers should maintain optimum, but not excessive nutrient levels to help the plants tolerate disease.
Early Blight on tomato foliage.