One of the diseases that can occur in desert melon production fields is Fusarium wilt. Symptoms on melons are similar to Fusarium wilt diseases on other plants, usually beginning as initial yellowing and wilting on one side of the plant or on one runner, followed by runner collapse. Internal discoloration of the xylem tissue at the base of the plant can be present as well. The xylem discoloration is usually light yellow to tan in color, not the dark reddish brown observed with lettuce. As the disease progresses, other runners will show symptoms and collapse, eventually leading to plant death. Fusarium wilt of cantaloupes and of watermelons are caused by two different specific forms of the fungal pathogen Fusarium oxysporum. For cantaloupes and other melons classified as Cucumis melo, the relevant pathogen is Fusarium oxysporum f. sp. melonis; whereas the pathogen for watermelon (Citrullus lanatus) is Fusarium oxysporum f. sp. niveum. In general, Fusarium wilt severity increases when plants are stressed due to high temperature, heavy fruit loads, and other plant growth stress factors. The use of resistant varieties is a useful disease management tool; however, the performance of a resistant variety can be affected by the inoculum level of the pathogen in soil. According to various published research articles, rotation out of melons from 3 to 10 years can significantly reduce but not eliminate the inoculum load of the pathogen in soil. There are numerous different forms of the Fusarium wilt pathogen, and each form has the capability of initiating disease on one or at most a few closely related types of plants. If you are concerned about planting melons in a former lettuce field known to have had Fusarium wilt, you have no need to worry. The Fusarium wilt pathogen of lettuce (Fusarium oxysporum f. sp. lactucae) will not cause disease on melons.

To contact Mike Matheron go to: matheron@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.