The fungi Verticillium and Fusarium can cause infectious wilt diseases of tomato. A number of plant samples have tested positive for wilt diseases this year. These soilborne fungi enter the root system of the plant and eventually plug the plant's vascular tissue. This leads to yellowing and wilting of plants leaves, usually working from the bottom of the plant upward. Infected plants die early, often producing little or no fruit.
In addition to the wilt symptoms, infected plants show a brownish-red discoloration of the vascular tissue in the lower stem. This can be visualized by cutting through the lower stem and crown tissue with a knife. The discoloration may extend up the stem some distance.
Tomato plants are available that are resistant to Fusarium and Verticillium wilt. The letter "F" associated with the cultivar name indicates resistance to Fusarium and the letter "V" indicates resistance to Verticillium. Resistance does not mean the plants cannot be infected. If the disease does occur, however, it will not be as severe as susceptible cultivars and a yield is usually obtained.
In addition to purchasing VF resistant cultivars, rotate away from crops in the tomato family (tomato, pepper, potato, and eggplant) for several years. This will help to reduce populations of the fungi in the soil. Also, plant tomatoes in a well-drained soil.
This article originally appeared in the August 11, 1995 issue, p. 120.