Verticillium wilt becomes evident when lower leaves on the vine turn yellow and wither. Symptoms progress upward until the entire plant yellows and wilts. Vascular tissue of stems becomes a light brown, which is best observed near ground level. Some tubers from infected plants may develop a light brown discoloration in the vascular ring near the stem end. Wilt causes early senescence of plants in heavily infested fields.
Life cycle
The fungus that causes Verticillium forms resistant structures that can survive for years in the soil in the absence of a living host. In the presence of a host plant, the resistant structures germinate and penetrate the plant's roots either directly or through wounds. Once inside the root, the fungus grows until it reaches the water-conducting cells, inside which it spreads upward through the plant, restricting water flow. Infection is favored by cool weather, but injury is most severe during periods of hot weather when plants are stressed for water.
Solutions
Verticillium wilt is caused by a soilborne fungus. Avoid soil previously planted with tomatoes, peppers, eggplant, or cucurbits. Rotate out of these susceptible crops and potatoes for 2 or 3 years. Legumes are good rotation crops. Following good sanitation practices and using soil solarization may help minimize problems. Some varieties are more tolerant than others.
