How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

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 hotter areas of 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.

MANAGEMENT

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 prevent the disease in furrow-irrigated fields.

PUBLICATION

UC IPM Pest Management Guidelines: Tomato
UC ANR Publication 3470
Diseases
R. M. Davis, Plant Pathology, UC Davis
G. Miyao, UC Cooperative Extension, Solano/Yolo counties
K. Subbarao, USDA Agricultural Research Station, Salinas
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgments for contributions to the disease section:
B. W. Falk, Plant Pathology, UC Davis