Alfalfa mosaic, caused by Alfalfa mosaic virus (AMV), is a viral disease that is becoming increasingly common in soybeans. Alternate hosts of AMV include alfalfa, other legumes and solanaceous crops. AMV is transmitted by aphids. Leaves have mottled patterns of bright yellow and dark green tissues. Newly emerged leaves may be smaller than usual with bright yellow spots and brown discoloration. Plants may be stunted. Plants infected by AMV do not produce seed with mottled seedcoats, unlike some other soybean viruses.
AMV is transmitted by more than 15 species of aphids, including the soybean aphid (Aphis glycines). Reports of alfalfa mosaic in soybeans have increased in recent years and are believed to be associated with outbreaks of soybean aphids. The disease may be more prevalent on edge of fields, especially in fields bordering alfalfa.
The best time to scout is anytime during the growing season. Check plants on the edge of fields and near alfalfa.
Variety selection: Resistance to AMV has been identified in soybeans, but is not yet commercially available. However, current soybean varieties differ in tolerance to AMV, based on degree of symptom expression.
Foliar insecticides: These are not likely to be effective in reducing transmission of AMV by aphids.
Photo by Craig Grau