Diseased tomato plant stalks

Southern blight damaged tomato plant

Updated: February 20, 2023

Wilting and collapse of individual stems or entire plants

When a plant or part of the plant (leaf, flower, fruit) rapidly collapses, wilts, and dies this is called blight. Many bacteria, fungi, and viruses can cause blights. Most blights are favored by certain weather conditions, such as hot and humid or cool and moist.

Southern blight is caused by the fungus Sclerotium rolfsii. This fungus can attack a wide range of vegetable crops and herbs and is seen with some frequency in Maryland on pepper and tomato. It is active only during hot weather, so plants can grow well in infested soil during most of the growing season, and only become damaged during the hottest part of the summer. The first symptoms seen are wilting and the collapse of individual stems or entire plants. Close inspection of the stem at the soil line reveals dark brown lesions, white mycelium (strands of fungus growing on the stem and mulch or soil surface), and small (1/8 to 1/16 inch), tan spherical sclerotia, that resemble mustard seeds (They are white when first formed, and gradually over several days turn brown). Roots of infected plants are often unaffected. Stem decay at the soil line is common during hot, humid weather.

southern blight on thyme
Thyme infected with southern blight
plant stem infected with southern blight
Closeup of infected stem


The basis for control of Southern blight is to reduce the number of sclerotia surviving in the upper few inches of the soil. During the growing season, remove wilted and blighted plants and the mycelium clinging to stems and mulch. Deep plowing can provide good control by burying the sclerotia. Keep the soil pH above 6.5 and add compost to garden beds on a regular basis.

The sclerotia are very resistant to heat and are not easily killed in compost piles. Throw out infected plants with household garbage or seal the plants in a clear plastic bag, expose them to full summer sun for 4 weeks and then put the plants through a hot compost process or dispose of in the trash.

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