My Tomato's Stem Is Rotting

Timber Rot

• Also called white mold, this disease is caused by a fungus, Sclerotinia sclerotiorum. The stem develops dark, watery-looking lesions that eventually girdle and kill the vine. Humid, moist conditions encourage the fungus to grow. Masses of white, cottony tissue, called mycelia, form on the stem, branch crotches or in wounds on the plant. If you cut open the stem, you will find mycelia inside, along with small, hard black growths the shape and size of small peas. No resistant varieties of tomatoes are available, so rotate tomato crops with other, nonsusceptible vegetables. Make sure the soil in the garden is well-drained, to discourage fungal development, and clear away all plant debris.

Bacterial Canker

• Difficult to diagnose without laboratory analysis, bacterial cankers form on the tomato stem long after the first symptoms of disease may be seen on the vine. Lower leaves turn downward and streaks run from the leaf midribs down to the stem, where the cankers then form. Cankers are lesions that may be white, raised spots with dark centers on the fruit, or sunken, rotted areas along the stem. Since the bacteria can live in the soil for years, do not plant tomatoes in that area of the garden next season. Dig up and destroy infected tomato plants. Collect and dispose of all plant debris.

Blight

• Another fungal disease, early blight or Alternaria leaf spot, appears during the hottest part of the summer. The fungus begins by causing black spots on older foliage, then moves on to infect the stems and fruit. The leaves turn yellow and drop from the vine. Remove dropped leaves and any other plant debris and dispose of it away from the garden. Don't plant tomatoes in the same spot next season. Make sure the plants have good air circulation, and water from the bottom rather than overhead since the fungus thrives in wet conditions. Use a sulfur dust to keep new growth from becoming infected.

Wilt

• Tomato spotted wilt/impatiens necrotic spot tospoviruses cause cankers on tomato stems and turns the leaves stiff. Wilt begins with spots on the leaves that spread to the stems. Yellow rings form on the fruit, and the plant may stop growing on one side. Remove infected plants and destroy them away from the garden. Weeds can harbor the virus, so keep the garden scrupulously weed free. Thrips -- tiny, winged insects -- transmit the virus while feeding on tomato plants.

Integrated Pest Management

• North Dakota State University's Cooperative Extension Service website offers guidance on preventing diseases in tomato plants. Use a multifaceted approach that includes buying only quality, disease-resistant varieties of tomato plants and seeds, rotate garden crops, clear plant debris after the final tomato harvest, and plow under anything that's left behind. Water with a soaker hose or other ground-level means, and avoid overwatering the tomato plants. Keep weeds out of the garden and control insect activity. Disinfect tools between uses and wash your hands before and after handling tomato plants. Avoid nicking or otherwise wounding the tomato plants while hoeing or using other tools in the garden. Use fungicides at the first sign of disease, if you know which disease it is. Follow label directions carefully.