Diseases of alfalfa (
Alfalfa mosaic virus
Alfalfa mosaic virus occurs in alfalfa throughout Arizona but does not cause losses. Infected alfalfa may have symptoms varying from mild mottling and yellowing of leaves to no symptoms at all. An entire field may have a very high percentage of infection but have no symptoms. The virus is transmitted by several different species of aphids, including the pea aphid and blue alfalfa aphid. It is transmitted in alfalfa by seed, and it is also sap transmitted, so it is easily spread by harvesting machinery.
There are many different strains of alfalfa mosaic virus, and they infect a large number of different plants. In Arizona, pepper planted close to alfalfa fields can be heavily infected as can other plants such as tomatoes, potatoes, lettuce, oregano, and basil. These alternate hosts usually have a bright yellow mosaic of the leaves (photo 1). The disease is appropriately called calico in these plants.
No control measures are used. The only control for other susceptible hosts is to plant them at some distance from alfalfa.
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December 27, 2007