- Stems will turn dark and rot when plants have been given too much water. This is called damping off. The roots usually rot first causing the plant to grow slowly and use very little water. Plants use little water during the winter, anyway, and continued irrigation when it is already moist brings on root and stem rot.
- Excess soil moisture provides conditions that are favorable for growth of fungi usually present in potting soil. Water plants only after the surface of the soil has had a chance to dry. This will usually prevent the fungi from rotting roots and stems. Be sure that pots have drainage holes to allow excess water and salts to leach out. Correct the conditions in the pot rather than mask the problem with fungicide treatments.
- Root rot can be detected by carefully inverting the plant and removing it from the pot so roots can be examined. Healthy roots should be creamy white. Diseased roots will be brown or black. It is difficult and usually not worth trying to save a plant with stem and root rot. Unless you have a family heirloom, discard the plant and start over.
- One way to prevent diseases spread when getting rid of a contaminated plant is to microwave the pot before putting a new plant in it. Wash the used pot with hot, soapy water and microwave the dripping wet pot for one to two minutes. The microwave kills spores and fungus that might be present. This process works for both ceramic and plastic pots, but not metal. To avoid melting, do not heat longer than recommended times. New pots do not need to be washed or microwaved.
Sherm Thomson - Utah State University Extension Plant Pathologist