By Darren Hefty
Just when you think you have things figured out, a new challenge pops up. In this case, that new challenge is the soybean vein necrosis virus (SVNV). While it doesn’t appear to be a game-changer for soybean production like glyphosate-resistant weeds have become, SVNV is still something to keep an eye on. Here are some details.
History
SVNV was first identified in Tennessee back in 2008 and has spread from Alabama to Michigan and from Kansas to New York and everywhere else in between. While we haven’t yet seen it on our farm in South Dakota, its presence was noted all throughout Iowa last year. One of the few good things about last year’s drought was that the SVNV never really amounted to much of a problem in Iowa and several other states due to the lack of moisture and the extreme heat. With some rain, the spread of the disease could have become more of a big deal.
How Does It Spread?
SVNV is usually spread by thrips. If you haven’t heard of or thought much of thrips, you need to pay attention to this tiny little insect now. Thrips are pretty common and can often be seen on the underside of leaves feeding right along the veins and elsewhere. Thrips prefer hot and dry weather like we had last summer.
Identification
Watch for small, light green to yellow patches running near leaf veins. At this point, this could be a symptom of several diseases; so it’s important that you keep scouting these discolored leaves to see what it could be. With SVNV, some people have described the advanced stages looking like a scratch that’s trying to scab over. The lesions become larger and brown and follow the leaf veins. Others say to watch for scalded reddish areas around leaf veins with browning veins especially on lower leaves. Obviously, things will look a little different depending on when you identify the disease.
Resistance?
Some soybean varieties are more tolerant than others. If you’re planting Group 3 and later, seedsmen are getting more familiar with which varieties are the most tolerant to SVNV. If you’re planting Group 2 or earlier, there haven’t been enough observations made to get a good feel for which varieties are the best. For that reason, spread your risk by planting several non-related soybeans.
Should I Worry?
SVNV has been classified as in the tospovirus family of viruses. It is likely they can survive in thrips that overwinter in certain parts of the country. Using a complete seed treatment package with one of the neonicotinoid insecticides (Cruiser, Poncho, Gaucho) should control early season thrips before they can reproduce and spread the virus further.
Will It Be a Problem in 2013?
It’s hard to guess from one year to the next which insects will be a problem, if any. It’s also impossible to predict the occurrence and/or severity of a disease. The weather conditions last year proved favorable for the spread of the thrips carrying the disease. Also, volunteer soybeans and possibly some weed species left alone in fields in the South allow the disease to spread from one crop season to the next; so burning them down or tilling them under is a good management practice.