This soil-borne fungal disease thrives in the warm soils and wet weather of the Southeast; it is sometimes called mustard seed fungus, a reference to the organism's small yellow resting bodies. It infects many commonly planted vegetables and flowers, some shrubs, and occasionally lawns. White, cottony growth appears on plant stems near soil level and often spreads to the surrounding soil. As the fungus gradually cuts off the flow of water through the stems, the plant rots at the base, turns yellow, and dies.
Control is difficult, because the fungus can survive in the soil for years without a host. Soil solarization will help; long (4-year) crop rotation is important. To minimize spread of the fungus, don't cultivate soil between plants after planting. In fall, clean up all debris and destroy infected plants, including their root balls. Till soil in winter to bury overwintering resting bodies.
For chemical control of Southern blight on ornamentals, consult your Cooperative Extension Office. There is no chemical control for edible plants.