Soybean Mosaic Virus
Soybean mosaic virus (SMV) occurs widely, but has been rarely detected in several surveys in the Midwestern U.S. recently. SMV can cause yield loss, affect seed quality, and reduce seed germination and nodulation. Yield reductions are generally low and infections late in the season cause little damage.
Symptoms of plants infected with soybean mosaic virus can range from no apparent symptoms to severely mottled and deformed leaves. Mottling appears as light and dark green patches on individual leaves. Symptoms are most obvious on young, rapidly growing leaves. Infected leaf blades can become puckered along the veins and curled downward. Soybean mosaic virus can cause plant stunting, reduced seed size, and reduced pod number per plant. The disease is one of several factors associated with discoloration of seeds, causing a dark discoloration at the hilum. Symptoms of SMV may not apparent when temperatures are above 90°F. Symptoms are often confused with growth regulator herbicide damage where the leaves will be elongated and which usually occurs in a pattern such as along a field edge. SMV can interact with bean pod mottle virus (BPMV) to create severe symptoms in plants infected with both viruses.
Conditions and Timing that Favor Disease:
Plants can be infected with SMV at any time during the growing season. Plants infected when young tend to show more symptoms than plants infected when older. Higher activity or populations of aphids favor virus transmission.
The causal agent of SMV is a virus. It has a wide host range including pea and snap bean. SMV is transmitted by aphids, sap, and by infected seed. Seed transmission rates appear to typically be below 5%, but can be higher or lower depending on the cultivar.
Use pathogen free seed. Planting early in the season may be helpful. Some cultivars may have some level of resistance to SMV. The value of insecticides to reduce SMV via controlling aphids is uncertain.