The brown spots on this tomato stem (below) are probably not due to late blight. Stem lesion with sporulation of the pathogen. Steve Johnson, University of Maine Cooperative Extension.) These plants are too severely affected to be saved.
Found on 25 July after an extensive heat wave ended with heavy rainfall.īelow: Plants with numerous initial symptoms of late blight. Click each image for larger viewsīelow: First symptoms on Long Island in 2013. Lesions (below) with growth and spores of the pathogen that developed while it was in a plastic bag over night.Ī single leaflet with a lesion is the first sign of late blight development in this garden. Established lesions cannot be controlled, even with the most effective systemic fungicides that can be used by farmers with a pesticide license.įuzzy growth on the underside of leaf lesions (below) is produced by the pathogen under moist conditions and consists mostly of spores. And it is destructive as diseased tissue is killed quickly. The disease can be very explosive due to the quantity of spores produced and the quick disease cycle under cool, wet conditions. The spores can be dispersed by wind to healthy plant tissue, infect the healthy tissue if it is wet for a few hours, and within a few days produce a new lesion. The fungal growth on the stems and also on affected leaves consist of thousands of microscopic spores. Next two images: These dark brown lesions on stems, with white fungal growth developing under moist conditions, are characteristic of late blight. See close-up images of those lesions in following images. The primary symptoms are stem lesions between the second and top lines. There is an affected leaflet below the bottom trellis line.
Image below shows initial symptoms of late blight on tomato in a garden.
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