Tomatoes are susceptible to several wilt diseases caused by soilborne organisms or environmental conditions. Wilt disease in tomato plants can often be confirmed by cutting into the lower stem and observing discoloration or staining of the vascular (food and water transport) tissues. Tomato wilts in the garden can be caused by fungi such as Verticillium dahliae and Fusarium oxysporum f. sp. lycopersici. Sometimes wilt, yellowing, and dying symptoms caused by these fungi appear on one side of the plant before the plant becomes completely affected.

Tomato wilt fungi survive for long periods of time in the soil. Gardeners may plant wilt-resistant tomato varieties by choosing those varieties designated as VF (Verticillium- and Fusarium-resistant) or VFN (VF plus N for root-knot nematode resistance). Practice long crop rotations (four to six years) in the garden with crops other than tomato, pepper, eggplant, and okra. Remove and destroy infected crop debris.

In southern states tomatoes are frequently affected by Southern bacterial wilt, caused by the bacterium Ralstonia solanacearum. Plants may rapidly wilt and die over a period of a few days. Vascular tissue of the stem near the soil line is brown and appears water-soaked when split open. You can confirm the presence of the bacteria by suspending a small piece of the stem base in a glass of water. The bacteria will "stream" out from the cut surface of heavily infected plants and will turn the water cloudy in an hour or so. Infected plants will not recover and should be removed and destroyed. The causal bacterium is soilborne and can survive in the soil for years. The most practical control is to avoid planting susceptible plants such as tomato, pepper, potato, sunflower, dahlia, geranium, marigold, or zinnia in the affected area. Rotation with nonhost plants for at least three years is recommended.

Tomatoes planted within the root zone of black walnut trees will wilt due to exposure to the toxin juglone, which is leached into garden soil from walnut roots. Walnut wilt causes many of the same wilt symptoms caused by the tomato wilt fungi and even causes a similar brown staining of the stem vascular tissues. Tomatoes should not be grown near walnut trees.

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Tomato Wilt Diseases