Symptoms and Signs
Tomato plants with southern blight have lesions on the stem at or near the soil line. These lesions develop rapidly, girdling the stem and resulting in a sudden and permanent wilting of the plant. White mats of mycelia are produced on the stem and in the adjacent soil. In a few days, tan to brown spherical sclerotia about 0.06 inch (0.5 mm) in diameter appear on the mycelial mat. The abundant sclerotia are a good diagnostic feature.
Comments on the Disease
Southern blight is not a common disease of tomatoes. High temperatures (above 85°F, 29°C) favor the disease, which occasionally causes damage to tomato crops grown in the Central Valley.
The fungus attacks a wide range of plants and survives for long periods in soil as sclerotia. Disease incidence and severity are dependent on the number of sclerotia in the soil.
- Rotate to nonhost crops, such as corn, sorghum, rice, or small grains, for at least 2 years to reduce inoculum.
- Deep plowing to bury plant refuse may help to destroy sclerotia.
- Keeping the tops of beds dry in tomato fields helps reduce the disease in furrow- and buried-drip-irrigated fields.