Timber Rot or White Mold

• Timber rot, also known as white mold, is a common fungal disease that affects many different crops, including tomatoes. Caused by a strain of Sclerotinia fungus, its symptoms begin as infected plants develop a water-soaked appearance. Most often, these symptoms develop on the plant's main stem close to the soil line. As it progresses, the plants wilt and die. Infected stems often crack open revealing white, cotton-like fungus surrounding small, black, pebble-like growths. Timber rot occurs in cool, wet weather, often following large amounts of rainfall.
  
  

Late Blight

• Tomatoes infected with late blight disease often develop pale green, water-soaked spots on the leaves, starting at the edges. As the disease progresses, the spots become surrounding by yellow or brown halos, developing a target-like appearance. During humid weather, the leaf spots are accompanied by a white, cottony mold developing on the undersides of leaves. Wet weather also contributes to the spread of late blight, and entire tomato plants may die after a few days of wet weather.
  
  

Powdery Mildew

• Powdery mildew is another common fungal disease that can affect tomato crops. Symptoms begin with the development of light green to yellow blotches on the upper surfaces of plant leaves. As the infection continues, powdery mildew causes leaves to turn brown, shrivel and die. The leaves become covered in a white, powder-like growth. Powdery mildew typically occurs in commercially grown tomatoes, especially those grown in greenhouses. According to gardening experts at the University of Florida IFAS Extension, the states most likely to develop powdery mildew in North Carolina, California, Nevada and Utah.
  
  

Control Options

• After identifying the fungi attacking the tomato plants, home gardeners may develop a plan to control the problems. Begin by sanitizing all garden tools both before and after working in the garden. Soak tools in a solution of one part bleach to nine parts water. Rinse off tools. Always sanitize after working with diseased plants before working on healthy plants. Control timber rot by carefully weeding the garden, destroying infected plants. For the next three years, plant tomatoes in another location to avoid soil contamination. Follow the same practices to control late blight. For powdery mildew, destroy infected plants and apply a fungicide approved for powdery mildew to the healthy specimens.