Southern Blight

• White cottony mycelium spreading outward from the stem base at or just below the soil surface — often appearing overnight when conditions are right
• Small tan or brown round structures (sclerotia) the size of mustard seeds embedded in or under the white mycelium — these are the overwintering bodies
• Stem tissue at the base turning brown and collapsing as the fungus girdled the plant
• Plant wilting rapidly and dying, usually over several days — the collar rot is complete before the upper plant shows distress
• Surrounding soil surface showing the characteristic white fan-shaped mycelial growth spreading outward from the dead plant
• Multiple nearby plants affected in sequence if the fungus spreads through moist soil in warm weather

Athelia rolfsii is a soilborne fungus most damaging in hot, humid climates — common in the southeastern United States and in any garden with warm, wet summer conditions. The fungus overwinters as sclerotia (hard, round bodies) in the top 2–3 inches of soil. Sclerotia can survive in soil for years. When soil temperatures exceed about 85°F and moisture is high, sclerotia germinate and mycelium spreads outward from the germination point, infecting plant stems at or below the soil surface. The fungus affects an exceptionally wide range of host plants — over 200 species — which means rotation alone cannot eliminate it from an infected bed.

1. 01Deeply till or turn infected soil in late summer to bury sclerotia below 4–6 inches, where they are less likely to germinate and reach the surface
2. 02Apply a 4–6 inch layer of compost mulch over the bed after tilling — the microbial competition in mature compost can suppress sclerotia germination
3. 03Remove infected plants immediately, taking the surrounding soil with the root ball and disposing of it in the trash — do not compost
4. 04Avoid overhead irrigation and morning watering that keeps soil surface wet during the hottest months
5. 05Solarize severely infected beds in midsummer: cover moist bare soil with clear plastic for 4–6 weeks to heat the upper soil layer above lethal temperature for sclerotia
6. 06Biocontrol products containing Trichoderma harzianum applied at planting have shown efficacy against Sclerotium rolfsii in some studies

If southern blight is recurring every season and solarization has not resolved the problem, your extension plant diagnostic lab can confirm the pathogen and advise on whether soil fumigation is a practical option for your situation.

• Southern Blight of Vegetables— University of Georgia Extension
• Southern Blight Management— UC ANR Integrated Pest Management