Identifying SMV-resistant soybean varieties is a high research priority in soybean production research. Photo courtsey of the University of Illinois.
Plant SMV-free seed
Infected seeds are the most important means that soybean mosaic virus is introduced into a soybean field. Therefore, planting SMV-free seed is an effective way of controlling the disease. SMV is seldom detected in weeds or other legume crops.
Late planting increases risk
Once established in a field, aphid vectors spread the virus when feeding. Late planting coincides with higher populations of the soybean aphid and increases the probability of transmission to young seedlings. Infection in the early growth stages has the greatest risk of yield loss and reduced seed quality, compared to infection later in the season.
Variety selection is the key
Disease resistance is the best long-term strategy to prevent yield losses from viruses. Growers are encouraged to ask their seed dealers about resistance to virus disease. Although most commercial soybean varieties are susceptible to SMV, resistance to SMV has been identified in soybean genotypes and varieties. Many promising genotypes have been identified in maturity groups appropriate for the North Central region and this remains a high research priority. It is likely that recommendations for SMV-resistant soybean varieties will be available to growers in the not-too-distant future.
Several promising lines have common parental backgrounds. Parker, (Minnesota Agricultural Experiment Station), and Colfax (Nebraska Agricultural Experiment Station), expressed low symptom severity. Archer (Iowa Agricultural Experiment Station) was also identified as a common parent.
Insecticides are not effective in reducing transmission of SMV by aphids
A cooperative study in Iowa and Wisconsin, funded by checkoff dollars, was conducted to determine if foliar application of insecticide recommended to suppress aphid populations would also reduce disease caused by soybean mosaic virus. The study concluded that SMV control cannot be obtained, even though aphid populations were suppressed well. The reason is that the insecticide does not eliminate the impact of numerous aphid species immigrating into the soybean field from transmitting the virus. Since previous studies conducted in Iowa before the introduction of the soybean aphid showed rapid spread of soybean mosaic virus by an array of diverse migratory aphid species, the migratory form of the soybean aphid is just added to the menagerie of aphids moving through the fields to transmit the virus.
The study also found that the colonizing form of the soybean aphid had little additional impact on disease spread, which was good news. So, since it doesn't take a lot of migratory aphids to generate a problem, the introduction of the soybean aphid into Iowa and Wisconsin will probably not make the problem worse; however, disease management cannot be obtained through attempts to control the aphids that transmit the virus.
The bottom line is that you shouldn't spray an insecticide below the soybean threshold since using an insecticide will only suppress the vector but not the disease and may make the virus problem worse.
Accurate diagnosis is important
Symptoms of SMV can be similar to other virus diseases. However, because virus infections involve specific combinations of virus, host, and vectors, the management strategies may be very different than for other viruses. If a virus problem is suspected, growers need to know the most prevalent virus or viruses involved. Most diagnostic clinics in the North Central region can perform serological tests that distinguish among soybean viruses.