DISEASES OF ALFALFA - ALFALFA MOSAIC

Another disease characterized by yellowing symptoms is alfalfa mosaic, caused by the alfalfa mosaic virus (AMV). This virus is transmitted by aphids, and once infection occurs, feathery, yellow lines and streaks form in the leaf tissue. A lack of any hyphal growth on the underside of the leaf helps distinguish this disease from downy mildew.

Control of leaf diseases is not typically of high priority in alfalfa production. For severe outbreaks of diseases such as spring black stem, common leaf spot, Stemphylium leaf spot and downy mildew, early harvest may be an option. This removes inoculum, and reduces humidity that may be favorable for pathogen growth and reproduction, and disease development. Because AMV is a systemic pathogen (i.e., it becomes distributed internally throughout the plant), early harvest is not an effective control. Where possible use aphid-resistant varieties. These varieties limit feeding and movement of aphids, and thus limit the movement of AMV as well.