Symptoms and Signs
Symptoms of alfalfa mosaic include bright yellow mosaic or calico pattern on leaves. Older leaves develop a yellow mottle with enlarged veins. Infected plants may be stunted.
Comments on the Disease
The host range of Alfalfa mosaic virus is very large (experimentally, Alfalfa mosaic virus has been shown to infect 430 plant species in 51 families). The virus is transmitted by many aphid species. Seed transmission of Alfalfa mosaic virus has been demonstrated in hosts such as alfalfa but not in lettuce. The primary inoculum source is probably nearby infected plants, especially alfalfa and certain weeds.
Control measures are usually not warranted because alfalfa mosaic is a minor lettuce disease. To avoid the disease, do not plant immediately adjacent to alfalfa or weedy areas.