Vegetable gardeners need to be on the lookout for late blight early during the 2010 gardening season. Late blight gets its name because it normally doesn’t pose a threat until late in the gardening season, but this year late blight has already been confirmed in Florida, Louisiana and Maryland.
You might be asking what is late blight? Late blight is a fungus disease of mainly tomatoes and potatoes. The late blight pathogen is Phytophtora infestans, which in Latin means ‘plant destroyer’. The pathogen can infect foliage, stems, fruit and tubers. The pathogen will show up on the leaves as a black lesion and can have white growth around the outer edge. The infection on the stem will usually occur where a leaf or group of leaves meet the stem and will appear as a brown greasy looking lesion. On tomato fruit, late blight will appear as a dark greasy looking lesion. The pathogen can be spread by wind blown spores and it favors warm moist conditions to multiply. It may overwinter in potato tubers or could spread to our area from developing strains in Florida that stay alive long enough to move up into our area as crops in other states develop.
For gardeners control will take a multi-step process. Gardeners should use clean transplants and tubers, use resistant varieties when available, control volunteer tomato and potato plants, and when there is a risk of late blight occurring use a fungicide program as part of management. Most fungicides work as protectant’s so they must be applied before the late blight fungus infects the plants. If late blight becomes severe the foliage or fruit that rot should be destroyed to eliminate them as a source of spores for plants that aren’t infected.
For help in identifying late blight symptoms contact your local Cooperative Extension Center.
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