The disease problems of basil are similar to those of other herbs. See Herbs for a detailed discussion of these diseases.
Plants develop a general or partial wilt.
The affected tissue can also turn dark and water-soaked. The water-conducting tubes inside the stem will become discolored. The fungus which causes the disease is seedborne. However, the fungus can persist in the soil for long periods of time once it is established. Control can be achieved by using clean seed and fresh potting soil.