Diseases of alfalfa (
Cercospora leaf spot
Cercospora leaf spot is caused by the fungus Cercospora medicaginis. Lesions form on leaves and stems when relative humidity is very high and temperatures are warm, 80 - 90 F. Disease is not common in Arizona because of the moisture requirement, but during summer rains or in overhead irrigated fields, disease may develop. When disease progresses, leaves may become yellow then shed. Stems then weaken and collapse (photo 1). Lesser infections may reduce hay quality.
Infected alfalfa should be cut as soon as possible to minimize loss and reduce reproduction and spread of the fungus. There is no resistance to disease in alfalfa, but certain varieties have more tolerance than others. For example, in greenhouse trials, CUF 101 was very susceptible while Mesa showed some tolerance.
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December 27, 2007