Diseases of melon (
Charcoal rot
Charcoal rot is caused by a soil borne fungus, Macrophomina phaseolina. This fungus is common in Arizona soils, and causes disease in wide variety of plants. The fungus produces microsclerotia, small black structures that develop under the cortical tissue of roots or on the surface of stem lesions, that enable the fungus to survive in the soil for many years in the absence of a host.
M. phaseolina has been associated with late season vine decline. In Arizona it is often isolated from pink colored root lesions and from rotted roots. In drip irrigated systems, M. phaseolina also causes water-soaked lesions on the stems and crown (photo 1) that may have an gummy exudate in which case the disease looks very similar to Gummy stem blight (photo 2). Vines with stem lesions have yellowing and death of leaves (photo 3). If lesions continue to develop, usually only very moist conditions of summer rains, plants may die. Fruit may also become infected, resulting in a firm, dark-colored decay.
There are no control measures currently recommended for charcoal rot. Cultural practices such as rotation, deep plowing and maintenance of soil moisture have not been effective. There has been little or no control using solarization or fumigation.
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July 30, 2003