It is that time of year again. Temperatures are rising, melon plantings are maturing, and sudden wilt and death of melon plants is occurring. What causes this sudden collapse of plants? In the desert melon production areas of Arizona and California, symptoms of melon plant wilting and collapse usually can be attributed to one of four diseases; Charcoal rot, Fusarium wilt, Monosporascus root rot, or Pythium sudden wilt. Each of these diseases is caused by a different soil-borne plant pathogen, so knowing what management options might be available first requires accurate identification of the responsible pathogen. Charcoal rot and Fusarium wilt, caused respectively by the fungal pathogens Macrophomina phaseolina and Fusarium oxysporum, are not effectively controlled by fungicides. Preventative actions that may reduce 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 stress factors such as fruit load and hot temperatures are obviously beyond your control. Monosporascus vine decline, caused by Monosporascus cannonballus, can be suppressed by application of the fungicide Cannonball at seeding or transplanting followed by additional applications as specified on the product label. The other disease mentioned was Pythium sudden wilt. Pythium, the pathogen that causes this disease, is a fungus-like soil-borne organism 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 identified 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. Knowing the melon disease history in a particular field can help immensely in preparing for possible recurrence of soilborne pathogen initiated diseases in a future planting.

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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.