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Soybean mosaic virus (SMV) is a common soybean disease that can cause reduced seed quality (including lower oil content), reduced seed germination and nodulation, and yield loss. Worldwide, SMV is currently one of the most prevalent and destructive viral diseases affecting soybean crops. SMV can reduce yield from 8% to 35% or more when combined infection happens with other viruses.¹
Learn to identify symptoms of SMV and discover how choosing the right soybean seed and using proper management practices can help mitigate the risk of soybean mosaic virus affecting your crop.
The primary concern with soybean mosaic virus is the damage and mottling it causes in soybean seeds. Mottling caused by an SMV infection hampers germination rates, lowers seed quality, reduces oil content, and can cause grain-grade reduction, especially in food-grade soybeans.
On average, yield losses due to soybean mosaic virus are very low; however, in rare cases, SMV losses as high as 94% have been reported. For instance, if soybean crops are infected with multiple viral infections (such as bean pod mottle virus in addition to SMV), this can lead to severe damage that can result in plant death and high yield loss.
Soybean mosaic virus has two primary modes of transmission:
📸:@Chiyacat via Canva/Featuring a soybean plant with a heavy aphid infestation
Symptoms of soybean mosaic virus are most severe during cool temperatures (lower than 77 °F), with SMV symptoms potentially disappearing with hot temperatures. Additionally, weather conditions conducive to aphid reproduction can increase the spread of SMV if the virus is already currently affecting the field. Aphid reproduction is most rapid in temperatures between 70 and 80 °F. Aphids typically do not survive temperatures over 90 °F.
Accurately diagnosing soybean mosaic virus is critical to managing it, since SMV symptoms can mimic those of other diseases or herbicide-inflicted crop injury.
The type and severity of SMV symptoms differ depending on the soybean variety, environmental conditions, and the growth stage of the plant at the time of infection. For example, the time between initial infection and the first appearance of symptoms can vary with temperature. Symptoms range widely: You may see no visible symptoms, or you may encounter severely mottled and deformed leaves.
Soybean mosaic virus symptoms include:
Foliar symptoms of SMV include mottled leaves displaying the namesake mosaic of light- and dark-green patches on individual leaves. These patches may become blistered over time. Additionally, infected leaves may be puckered along the veins and curl downward. Scout for foliar symptoms of SMV in cool weather when plants are in active growth stages, since SMV infection is most visible in young soybean leaves.
📸:@Craig Grau and the University of Wisconsin-Madison Teaching Images, bugwood.org/Featuring a soybean plant showing foliar symptoms of soybean mosaic virus.
Soybeans infected with mosaic virus will usually exhibit stunted growth and smaller-than-normal seed sizes and will produce fewer pods per plant. Plants affected by SMV will likely have shortened petioles (the stalk at the base of the leaf that attaches the leaf to the plant stem and internodes) and internodes (the portion of a plant stem between two nodes). SMV-infected pods typically have less hair and are smaller, flat, and more curved than healthy pods.
SMV hampers soybean seed germination and may cause seed discoloration. Seed abnormalities may include a dark discoloration at the hilum (the eye, or point of attachment of the seed to the pod) or a mottled black or brown pattern, depending on hilum color. However, seed mottling alone does not indicate that SMV is present in the seed since some SMV cases do not show signs of seed abnormalities.
📸: @Oleh Malshakov via Canva/Featuring normal, healthy soybeans germinating in soil.
Unfortunately, there are no chemical treatments available to control SMV. While it may seem promising to try to manage SMV by controlling the aphids that contribute to its spread, research concludes that reducing aphid populations with foliar applications of insecticide is ineffective at reducing damage from SMV.⁴
The good news is that there are several proactive soybean mosaic virus control practices that can help reduce the risk of your field becoming infected.
Since SMV is typically introduced into a soybean field via infected seed, it is vital to ensure you are planting seed that is certified SMV-free to control the disease. You can submit a seed sample to a plant pathology lab to determine if it is SMV free.
Most commercial soybean varieties are susceptible to SMV, but some resistance to SMV has been identified in soybean genotypes and varieties. If a resistant soybean can stop the replication and movement of the virus, it can prevent disease spread, and the resistant plant will display no symptoms of SMV.⁵ Ask your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative about which soybean varieties provide the best virus-resistant genetics.
Soybean crops are at the greatest risk of yield loss and reduced seed quality when SMV infections occur in the early growth stages compared to later-season infections. If your field is infected with SMV, higher populations of soybean aphids will be able to take advantage of late-planting conditions that are favorable for aphid reproduction, increasing the risk of SMV damage. Planting soybean crops early can help you mitigate this risk.
Read more about soybean crop threats and how to manage them:
Experts are available to help you make your decisions. Reach out to your seed retailer, a nearby extension office agent or a seed company professional like your regional BASF representative.
This content is being brought to you in partnership with Grow Smart® Live and contributing guest authors. BASF provides the information in this article as a service to its customers; however, the views expressed by guest writers are their own and do not necessarily reflect the views of BASF.
Grow Smart® Live is a registered trademark of BASF. Copyright 2024 BASF Corporation. All rights reserved.
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January 9, 2025
