Tomato Fusarium Wilt

If your tomato plants wilted and yellow on one side of the plant or one side of a leaf, they have Fusarium wilt. Fusarium wilt on tomatoes caused by Fusarium oxysporumsp. lycopersici. It is a fungus soilborn found in the United States, especially in hot regions of the country. The organism is specific to tomato and many longlived in all regions of the United States. The disease develops rapidly in soils that are high in nitrogen and low in potassium. In addition, plants grown in sandy soil tends to contract the disease more often.

Symptoms

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).

Fig - 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.

Fig 2

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). 

Fig 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.

Fig 4

Life Cycle

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

Because Fusarium and Verticillium fungi are widespread and persist several years in soil, a long crop rotation (4 to 6 years) is necessary to reduce populations of these fungi. Avoid using any solanaceous crop (potato, tomato, pepper, eggplant) in the rotation, and if Verticillium wilt is a problem, also avoid the use of strawberries and raspberries, which are highly susceptible. Rotate with cereals and grasses wherever possible.

Keep rotational crops weed-free (there are many weeds hosts of Verticillium).

Whenever practical, remove and destroy infested plant material after harvest.

Maintain a high level of plant vigor with appropriate fertilization and irrigation, but do not over-irrigate, especially early in the season.

Plant disease resistant tomato varieties, labeled V (for Verticillium) and F (for Fusarium). These disease resistance designations are usually shown in seed catalogues. Fusarium- or Verticillium-resistant varieties of eggplant, potato, and pepper are generally not available.

If soils are severely infested, production of solanaceous crops may not be possible unless soil fumigation is an option. See the Ohio Vegetable Production Guide (OSU Extension Bulletin No. 672) for information on soil fumigation.