Soybean Mosaic Virus

SMV

Potyvirus

Soybean leaves crinkled and misshapen by Mosaic Virus infection. Photo courtesy of Daren Mueller. {{CCBY3.0}}
Soybean leaves crinkled and misshapen by Mosaic Virus infection. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
SMV is a virus spread by aphids that causes plants to be stunted and often result in lower quality seed. In some areas it is not much of a concern, while in other areas it has caused up to 35 percent yield loss.
SMV can be transmitted through seed or aphids, and usually overwinters in perennial weeds or aphids. It can only be transfered via a live host, and the transmission rate in aphids (the most viable transmitter) is usually about 5 percent. It is known to infect plants throughout the growing season.
SMV symptoms can be nonexistent in some cases or result in severely mottled and deformed leaves. Mottling ranges from light to dark green and is most obvious in young leaves that are in growth spurts. Leaf blades that become deformed begin puckering around the veins and then curve downwards. Overall, the plant's growth and development is stunted while the pods and seeds are reduced in number. Symptoms can be exasperated if the plant is also infected by bean pod mottle virus (BPMV). Younger plants tend to be more symptomatic.
SMV is known to cause yield loss, affect seed quality, and reduce seed germination. Infections late in the season usually cause very little damage. In combination with BPMV, yield losses can be much higher. Along with higher terminal death, there is a greater chance of seed transmission. Soybeans infested with aphids are at a higher risk for contracting the virus. Losses have been reported to range from 5 to 35 percent, with severe cases resulting in 94 percent loss.
Be sure to use seed that does not have the pathogen in it. Planting late is more conducive to soybean aphid infestation, as infection in early growth stages can be the most detrimental.
Insecticides may be used to control aphid populations, but studies have shown that it has virtually no net positive effect on the spread of the virus. This is because immediately following the eradication of aphids in the field, new swarms will enter the area, possibly carrying in other viruses. Please contact your local plant pathologist to learn what is most effective in your area and how to use it best. Always read and follow all label instructions.
Some varieties of soybean have resistance to SMV.