Extension scientists identified Southern blight in a tomato planting in mid-June. Southern blight is a soil-borne fungal disease and is a problem on tomatoes and other broadleaf crops.
The disease thrives under moist conditions and high temperatures. Initial symptoms include leaf yellowing and wilting of infected plants. A black discoloration of the stem at the soil-line is often visible. The stem may become covered with a white fungal growth under moist conditions. This growth is also visible on fruit in contact with soil and on crop debris. Round, tan, mustard-seed size sclerotia often form in the mycelium.
The fungus is spread as mycelium in infested organic matter, or as sclerotia in infested soil. The fungus may spread more than 3 feet through the soil, often killing adjacent plants within a row.
For control, do not plant tomatoes or other broadleaf crops in the same area more than once every 3 to 4 years. Deep-plowing the soil to bury crop debris and sclerotia will help reduce inoculum. Wider plant spacing and removing infected plants as soon as symptoms are visible may slow development and spread of this disease.
Soil drench-type fungicides used at transplanting may reduce damage. There are a few foliar fungicides that offer suppression of the southern blight. Please refer to the Southeastern Vegetable Crop Handbook for fungicide recommendations.