Soybean mosaic virus (SMV) is currently not a production problem in Iowa because disease levels are very low. However, this virus disease is seedborne, and to prevent problems in the future, efforts must be made now to prevent the build-up of this disease in seed sources.
The main concern about SMV is the effect on seed quality. Virus-infected plants may produce fewer, smaller, and often mottled seed. Infection in the early growth stages has the greatest risk of yield loss and reduced seed quality, compared to infection later in the season.
Another concern about SMV is dual infection with other viruses, a common situation that increases the risk of yield loss and reduced seed quality. SMV and Alfalfa Mosaic Virus often occur together in the same plant. Tobacco Streak Virus and Bean Pod Mottle Virus (BPMV) have also been found in multiple infections.
Common leaf symptoms of SMV are a mosaic of light and dark green areas, chlorosis, rough leaves, and leaf curl.The youngest and most rapidly growing leaves show the most symptoms, especially at cooler temperatures. Plant stunting, reduced pod numbers and seed discoloration are also symptoms of SMV infection.
Infected seed is the most important way that SMV is introduced into a soybean field. Once the virus is in the field, aphids can spread it from plant to plant as they feed. Over 30 species of aphids transmit SMV worldwide. Recent research confirmed the soybean aphid, (Aphis glycines ) is a vector of soybean mosaic virus.
Management of Soybean Mosaic Virus
Symptoms of SMV can be similar to other virus diseases. Because effective management depends on accurate virus identification, growers need to know what is causing the most prevalent virus problem in a particular field. The ISU Diagnostic Lab and the ISU Seed Science Center can assist you in making an accurate diagnosis.
Seed transmission of SMV depends on variety and ranges from 0-5% in most modern soybean varieties. If you save seeds for next season, check your seeds for virus infection if you find that a significant proportion of your seeds from an aphid-infested field are discolored.
Most commercial soybean varieties are susceptible to SMV. However, resistance to SMV has been identified in soybean genotypes and varieties, and it is likely that recommendations for SMV resistant soybean varieties will be available to growers in the near future.
Insecticides are not considered effective in reducing transmission of SMV by aphids. Aphids present at spraying are killed, but the field is quickly recolonized by winged aphids and virus transmission can resume. Aphids that contact insecticide residues on the leaf surface are killed, but are still capable of virus transmission prior to death.
Research on the longer-term management strategies for this pest complex is in progress. Continue to check at the ISU Integrated Crop Management newsletter for the latest findings and recommendations for SMV and soybean aphid management.