Posts Tagged ‘soybean vein necrosis virus’

Soybean Disease Update – September 23, 2011

Friday, September 23rd, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Soybean Vein Necrosis Virus
I just wanted to add a brief summary for our WCU readers that soybean vein necrosis virus has been seen in all three counties in Delaware and apparently is widespread in the surrounding states of PA, MD, and VA. We see it everywhere we look now but I am not sure how much effect it is having on yield at this point. Researchers in other parts of the country are also working on it and have a few more years experience with it. It is premature to say too much about it other than we now know what is causing the symptoms we have seen this year and probably last year as well, but did not know what it was. By the time the winter meetings occur hopefully I will be able to share more hard facts about the disease and control options for our region.

Early symptoms of soybean vein necrosis virus (SVNV) from DE

Soybean Cyst Nematode
Do not ignore soybean cyst nematode. Soil sampling after harvest before any fall tillage is recommended for fields to be planted next season to soybeans following this year’s crop. Do not plant SCN susceptible varieties without soil testing first. Soil sample bags and information sheets are available from the county Extension offices for $10/ sample bag.

Soybean Rust Risk Assessment (ZedX, Inc. & PSU)
Despite recent heavy rainfall along the Atlantic Coast and throughout the Northeast from the remnants of Lee and Hurricane Irene, source inoculum in the Southeast was likely still too low to cause widespread transport and deposition of spores further north. Soybean rust was, however, identified in extreme southwestern Georgia for the first time this season. Due to the ongoing drought in Texas and Oklahoma, the slow progression this season in the Southeast, and the fact that the primary soybean production season is in the later stages, it is unlikely that soybean rust will spread as far as it has in years past. As such, the risk area will remain rather minimal in spacial coverage (see map below). Double crop soybeans along the Gulf Coast could still be at risk for soybean rust as the season progresses, but even double cropped soybeans are at a minimal risk.

The above image displays the current threat level of soybean rust. The yellow “wait” areas are considered slightly at risk, orange “watch” areas are at moderate risk, and red “warn” areas are at great risk or already identified positive for soybean rust. Risk areas are estimated based on meteorological factors affecting spore transport and deposition and factors conducive for further development within the canopy such as temperature and moisture. Biological factors such as host plant and crop phenology are also considered. Risk assessment maps are produced by the PSU Ensemble Field Crop Rust Forecasting Program.

Soybean Vein Necrosis Virus Confirmed in DE, MD and VA

Friday, September 16th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Soybean vein necrosis virus was confirmed this week by Dr. Yannis Tzanetakis, Department of Plant Pathology at the University of Arkansas. So the symptoms that we have been seeing and sharing with concerned growers are due to this new virus disease. Although I say it is new, some of the first symptoms were seen in 2008 in Tennessee and Arkansas. The subsequent work by the researchers at Arkansas discovered the new virus. They were able to report that this new virus disease, soybean vein necrosis virus (SVNV), belongs to a group of thrips-transmitted viruses. This group called the tospo viruses includes several that we see in greenhouse production in the region and in the field occasionally, namely tomato spotted wilt virus and impatiens necrotic spot virus.

 Early symptoms of soybean vein necrosis virus (SVNV) from DE

This group of viruses are acquired by thrips feeding on infected plants and once acquired then the virus can be transmitted by the thrips for the rest of its life. We call this a persistent virus in the vector and this may allow us to control SVNV by controlling thrips. This is very preliminary and much work is being done in the Midwest to identify the thrips vectors and possible other hosts of the virus that may harbor it and allow thrips feeding to move it to soybeans. It is too early to know if that strategy will work practically. The question we all have is: will it reduce yield here or affect seed quality? So far I have not seen enough leaf loss to imply that some yield effects are possible. But we have some time to go before maturity, so the jury is still out on the yield effects here in the Mid-Atlantic. Fortunately this group of viruses is not known to be seed-transmitted and that is being addressed by these researchers.

The researchers from Arkansas have noted that often a single virus infection may not have much of an effect but multiple infections with other viruses may increase yield loss potential. We have occasional outbreaks of bean pod mottle virus and we have seen soybean mosaic virus and peanut stunt virus in soybeans in the region, so the potential is here for multiple infections. We do not have much information about the extent of other virus diseases in soybeans.

The other avenue of control is identifying sources of resistance and evaluating current soybean varieties for resistance. Ideally identifying sources of genetic resistance that are incorporated into good varieties will be best control strategy. That work is ongoing as well. It is too early to be making recommendations but growers need to be aware of this disease and know that work is being conducted to answer some of these pressing questions.

Also, do not ignore soybean cyst nematode. Soil sampling after harvest before any fall tillage is recommended for fields to be planted next season to soybeans following this year’s crop. Do not plant SCN susceptible varieties without soil testing first. Soil sample bags are available from the county Extension offices for $10/ sample bag.

Possible New Virus Detected in Delaware, Maryland and Virginia Soybeans

Friday, September 2nd, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

We have seen samples from DE and MD with unusual leaf spot symptoms that are often limited to the veins. There is a yellowing and reddening of the tissue and veins associated with the virus infection. The symptoms can progress to a necrosis of the tissue around the veins as well. This virus disease, soybean vein necrosis virus, once it has been confirmed, would be new and a first report for our area. It has been seen in parts of the Midwest and confirmed by researchers at the University of Arkansas. They have seen pictures of the samples we have received and are sure it is SVNV. If you have seen these symptoms on soybeans we would like to know about it, and receive some leaf samples. There are differences in susceptibility to this new virus among varieties so we would need to know what variety you are growing if you see these symptoms. There may be some confusion about these symptoms because they can resemble Cercospora leaf blight caused by Cercospora kikuchii, which also causes purple seed stain.

Symptoms associated with soybean vein necrosis virus.