A problem encountered by some home gardeners in recent weeks is the sudden wilting of tomato plants. The two most likely causes of wilting are vascular wilts and stalk borers.
The initial symptoms of Verticillium and Fusarium wilts are wilting of the plant leaves during the heat of the day. Affected plants often recover in the evening or overnight. Gradually, however, the wilting becomes progressively worse and many plants eventually die.
Verticillium and Fusarium wilt are caused by soil-borne fungi that invade tomato plants through injured roots. The fungi spread into the water-conducting tissue (xylem) in the stem and block the flow of water to the foliage. Foliage of affected plants turns yellow, then wilts and dies. A cut through the lower stem of a dead plant often reveals a brownish discoloration of the vascular tissue.
There is nothing that can be done for plants that have Verticillium or Fusarium wilts. Plants that die should be removed and destroyed. Crop rotation is of limited value as the vascular wilt fungi may survive in the soil for several years. The use of resistant varieties is the most practical way for home gardeners to prevent losses due to wilts. Resistant varieties may become infected but many plants survive and produce an acceptable crop. Resistant varieties are available in seed catalogs and at garden centers. The letters V and F following the variety name in seed catalogs or on seed packets denote varieties that are resistant to Verticillium and Fusarium wilts. Wilt resistant tomato varieties that perform well in Iowa include Jetstar, Better Boy, Burpee VF, and Celebrity.
The stalk borer is an insect pest that attacks a wide variety of plants including tomatoes, potatoes, peppers, corn, hollyhocks, and dahlias. The larva (caterpillar) bores into the stem and tunnels inside the stalk. (The entrance hole is small and often difficult to locate.) Affected plants wilt and often die. However, stalk borer damaged plants that are given good care may survive.
Please refer to the article on stalk borers in Entomology (this newsletter) for additional information.
This article originally appeared in the July 1, 1994 issue, p. 105.