Fusarium wilt can occur in Yuma area melon fields and has already been detected in a melon planting this season. Symptoms of Fusarium wilt on melons are similar to Fusarium wilt diseases on other plants and include 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 occur as well. As the disease progresses, other runners will show symptoms and collapse, eventually leading to plant death. Fusarium wilt on cantaloupes and on watermelons is each caused by a specific form 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 temperature extremes, heavy fruit loads, or other plant growth stress factors. The use of resistant cultivars is a useful disease management tool; however, the performance of a resistant cultivar can be affected by the inoculum level of the pathogen in soil. According to published articles, rotation out of melons for from three to 10 years, depending on the report, will 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. No worries about planting melons in a former lettuce field known to have had Fusarium wilt. 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.