Verticillium wilt of tomatoes and potatoes
Verticillium wilt of tomatoes and potatoes can be caused by two different soil-borne fungi, Verticillium albo-atrum or Verticillium dahliae. These fungi have a very broad host range, infecting up to 200 species of plants. In addition to tomatoes and potatoes, these fungi can infect cucumber, eggplant, pepper, rhubarb, watermelon, artichoke, beet, broad bean, strawberries, raspberries, and a number of weedy plants. They may also infect several woody species such as maple, ash, lilac, smokebush and roses. For information on how this disease affects woody plants, see the University of Minnesota Extension Publication Verticillium Wilt of Trees and shrubs.
Wilting is the most characteristic symptom of infection by Verticillium spp. Symptoms usually appear on the lower leaves in mid-August when infected plants wilt during the warmest part of the day, and then recover at night. Leaf edges and areas between the veins turn yellow and then brown. In addition, infected plants often have a characteristic V-shaped lesion at the edge of the leaf occurring in a fan pattern. These foliar lesions can enlarge, resulting in complete browning and death of the leaves.
Verticillium wilt can be detected by looking for the presence of vascular streaking in stems near the ground. When cut longitudinally, Verticillium-infected stems show a light tan discoloration of the vascular tissue (Figure 1). These symptoms are similar to those caused by another fungus, Fusarium, but vascular streaking caused by Fusarium is generally darker and progresses further up the stem than streaking caused by Verticillium. Infected potato tubers may also show similar vascular discoloration occurring in rings, especially near the stem end (Figure 2). Although discolored, the tubers are safe to eat.
Wilt caused by this disease may be differentiated from drought-stress based on the portion of the plant that is wilting and on the location of wilted plants. Diseased plants often have only a portion of the plant wilting, such as one or two stems (Figure 3). In addition, diseased plants usually appear in patches within the growing area (Figure 4). Plants suffering from drought, however, are uniformly wilted and occur throughout the growing area.
The fungi causing this disease overwinter in the soil as mycelium or on plant debris as microsclerotia. The fungi infect a susceptible host through wounds in the roots caused by cultivation, nematodes (microscopic worms), or the formation of secondary roots. This disease is considered a cool-weather disease, developing between 65° and 83°F.
Management of this disease is difficult since the pathogen survives in the soil and can infect many species of plants. As with many diseases, no single management strategy will solve the problem. Rather, a combination of methods should be used to decrease its effects. When a positive diagnosis has been made, the following recommendations may be followed:
- Whenever possible, plant resistant varieties. There are many Verticillium-resistant varieties of tomatoes. These are labeled "V" for Verticillium-resistance. There are no potato varieties that are resistant to Verticillium, though some varieties are tolerant. The pepper variety 'Giant Szegedi' is reported to be Verticillium-resistant. Note: Verticillium-resistant plants may still develop Verticillium wilt if there is a high population of nematodes in the soil.
- Remove and destroy any infested plant material to prevent the fungi from overwintering in the debris and creating new infections.
- Keep plants healthy by watering and fertilizing as needed.
- Gardens should be kept weed-free since many weeds are hosts for the pathogen.
- Susceptible crops can be rotated with non-hosts such as cereals and grasses, although 4 to 6 years may be required since the fungi can survive for long periods in the soil.
- Soil fumigants are effective in reducing disease severity, but are not recommended for home use.
|Verticillium-resistant Tomato Varieties||Verticillium-tolerant Potato Varieties|
For more information, see the following websites:
Fusarium and Verticillium Wilts of Tomato, Potato, Pepper, and Eggplant, The Ohio State University Extension Fact Sheet
Verticillium Wilt, Plant Disease Lessons, American Phytopathological Society
Verticillium Wilt of Tomato, Cornell University Vegetable MD Online