Diseases of melon (
Alternaria leaf spot
Alternaria leaf spot is caused by the fungus Alternaria. The fungus produces dark, multicelled spores on host tissue only when there is substantial moisture, usually during summer rains. The spores are easily carried in wind and splashing water and infect only the leaves. Brown necrotic spots appear on the leaves wherever spores germinate and infect leaf tissue (photo 1). Spots are small at first then may enlarge and coalesce to form circular lesions with visible concentric rings (photo 2).
Disease severity is dependent on varietal susceptibility and environmental conditions. Extended periods of moisture and warm temperatures favor disease development. Applications of fungicides, chlorothalonil or mancozeb, are preventive only, so fungicides should be applied regularly at the onset of summer rains to fields or plants in areas where disease is known to have occurred previously.
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July 30, 2003