By Nathan Kleczewski
Extension Plant Pathologist
Soybean Vein Necrosis Virus (SVNV) is a relatively new virus of soybeans. Currently, SVNV is the most prevalent virus in soybean production in the United States. Surveys in Delaware in 2015 detected the virus in over 72% of fields, with 69% of full season and 93% of double crop beans infected to varying levels. The virus is known to be spread persistently by thrips.
A leaf with a low level of SVNV symptoms. Note how the lesions originate from the veins.
Thrips pick up the virus from an infected host early in their development and can spread it throughout their lifespan. Thus, greater exposure to thrips should be related with increased levels of SVNV symptoms. In 2015, this was the case, as Delaware Soybean Board-funded field surveys and small plot trials showed that double crop beans had greater levels of SVNV symptoms than full season fields/plots. The idea is that there are more thrips earlier in the double crop season, allowing for more pronounced symptoms and potential yield/quality effects. We also noticed significant differences in symptomology as a result of variety. What causes a variety to express less symptoms is not currently known.
Results from the 2015 Delaware soybean survey. SVNV symptoms were greater in double crop soybeans as compared to full season soybeans.
SVNV as impacted by variety and planting date. Green = full season. Yellow = double crop. Clearly, full season beans showed greater SVNV symptoms as compared to double crop beans. Varieties differed in symptomology, with 74B42R having significantly lower symptoms than other varieties across both systems. From Kleczewski et al 2015.
In addition, a recent paper in the journal PLOSone shows that the virus not only can be spread by thrips, but also in seed. Researchers in the Midwest were able to detect the virus in symptomatic seed and asymptomatic (no disease apparent) plants growing from the infested seed lot. This is the first time a virus in this particular viral family has been shown to be transmitted in seed.
Research into SVNV continues, and there is much progress being made in this area. We are still learning much about this virus and what potential impacts it may have. Thus, there are no management recommendations at this time. However, be aware of this virus and what symptoms look like. It is easy to misidentify SVNV symptoms as being caused by fungal diseases. Obviously, fungicides will have no impacts on a virus.