Temperatures are increasing, melon plantings are maturing, and sometimes sudden wilt and death of plants is occurring. What is causing this condition? In the desert production areas of Arizona and California, the symptoms of melon plant wilting and collapse usually can be attributed to one of four diseases, Charcoal rot, Fusarium wilt, Monosporascus root rot and vine decline, or Pythium sudden wilt. Each of these diseases is caused by a different soil-borne plant pathogen, so knowing what management options are available first requires accurate identification of the responsible pathogen. Charcoal rot, Fusarium wilt, and Monosporascus rot and vine decline, caused by Macrophomina phaseolina, Fusarium oxysporum, and Monosporascus cannonballus, respectively, are not effectively controlled by fungicides at this time. Preventative actions that may lessen the severity of these diseases include planting resistant melon varieties when available (for Fusarium wilt) and minimizing plant stress. Plant stress due to over- or under-irrigation can be managed; however, other crop stresses due to fruit load and hot temperatures are obviously beyond your control. The other disease mentioned, Pythium sudden wilt, was associated with significant losses of plants last season in several watermelon plantings. Pythium is a fungus-like pathogen that can be managed by fungicides, such as mefenoxam. However, the difficulty in preventing extensive Pythium sudden wilt is that once this disease is initially detected in a field, rapid deployment of an effective fungicide treatment will protect noninfected plants but may not save plants already infected but not yet displaying sudden wilt symptoms.

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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.