Alfalfa Mosaic Virus Detected in Soybeans Back »

Figure 1. Alfalfa mosaic virus symptoms on soybean. Credit: E. Byamukama

Written collaboratively by Emmanuel Byamukama, Connie Strunk, Connie Tande, Marie Langham, and Adam Varenhorst.

Alfalfa mosaic virus-like symptoms (Figure 1) were found at a very low incidence in a few soybean fields scouted last week. Leaves from the potentially infected plants were subjected to laboratory test and were confirmed to be positive for Alfalfa mosaic virus (AMV). Some of the soybean fields that were found with AMV were adjacent to an alfalfa field.

Symptoms & Transmission

Alfalfa mosaic virus causes bright yellow mosaic patterns on the leaves. Infected leaves may also be distorted or have a rough leaf surface (rugosity). Symptom severity may vary from soybean cultivar to cultivar and will also depend on the time of infection. Sometimes infected plants may recover from infection and become symptomless later in the season. Alfalfa mosaic virus is transmitted by over 15 species of aphids including the soybean aphid. It can also be seedborne but the rate of AMV seed transmission is very low. Aphids can acquire AMV from alfalfa plants or weeds such as black night shade (Figure 2 and Figure 3) and transmit it to soybeans.

Figure 2. Alfalfa mosaic virus symptoms on alfalfa.
Credit: E. Byamukama
Figure 3. Alfalfa mosaic virus symptoms on a black nightshade weed within an alfalfa field.
Credit: E. Byamukama



Select soybean cultivars with AMV resistance if AMV has been observed in the area. Insecticides may not be effective in controlling AMV since aphids may be agitated to move and transmit the virus before dying. In addition, aphids other than the soybean aphid may be responsible for transmitting the virus but will not colonize soybean. Follow the recommended soybean aphid threshold before applying insecticides. Weed control may help in reducing the inoculum both in alfalfa and in soybean fields.

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