Calico (Alfalfa Mosaic)


Calico diseaseLeaves of infected plants are very noticeable, clearly stand out in a field. They are bright yellow with a smooth surface, often shiny. Tubers may mis-shape and crack.

The pathogen is the Alfalfa Mosaic Virus (AMV) and it is carried by many aphids affecting alfalfa and clover, and sometimes around wheat.
Spread is from near-by alfalfa and clover fields often just after the time of cutting or harvest as the aphids fly away from these fields into potato fields where water is present. Aphids become the virus and deposited all in only a few plant visits (non-persistent).

Although the problem is not usually a major concern, sections of fields can be severely affected. By planting over a mile from an alfalfa or wheat field will eliminate any problem. If planted near these fields, an aphid control program may be needed. Controlling volunteer alfalfa is helpful. The problem appears worst when a circle is planted partially in potato and partially in alfalfa.