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New disease, insects threaten Virginia soybeansNew disease, insects threaten Virginia soybeans

• A new disease to Virginia, soybean vein necrosis virus (SVNV), has spread into soybean fields and may cause a problem for growers in the 2012 season.• This year Virginia soybean growers will likely see kudzu bugs in large numbers.• Each of these pests are a threat to soybean yields and to profitability of the crop in Virginia.

Roy Roberson 2

June 11, 2012

5 Min Read
<p> SYMPTOMS of soybean vein necrosis virus.</p>

Virginia soybean growers got their first taste of brown marmorated stink bugs last year and just a glimpse of a new soybean disease called soybean vein necrosis virus.

This year they will likely see kudzu bugs in large numbers.

Each of these pests are a threat to soybean yields and to profitability of the crop in Virginia.

Soybean prices are likely to remain high for the 2012 crop and acreage across the Southeast is likely to react to price. Virginia Tech Soybean Specialist David Holshouser says in some areas of the state input costs are already pushing $10 a bushel, and the prospect of dealing with new pests is almost certainly going to push these costs higher.

A new disease to Virginia, soybean vein necrosis virus (SVNV), has spread into soybean fields and may cause a problem for growers in the 2012 season.

This disease is transmitted by thrips in much the same was as tomato spotted wilt virus is transmitted.

The record warm winter of 2011-2012 and other factors indicates a heavier than usual thrips flights. If infestations are heavy in the later part of the thrips season, it would bode well for transmittal of SVNV.

Soybean vein necrosis virus belongs to a group of thrips-transmitted viruses called the tospo viruses. The most common and damaging of these viruses in row crops in the Southeast is tomato spotted wilt virus.

Pat Phipps, long-time Virginia Tech plant pathologist, says SVNV showed up for the first time in Virginia soybeans last year. The disease causes yellow blotches initially and as they start to darken, yellowing in the vein of the plant develops.

How much yield damage this disease can cause in soybeans in the Upper Southeast isn’t known. It has been found sporadically in Kentucky, Tennessee and Arkansas since 2008, but it is so new to Virginia and the Upper Southeast that researchers have not had time to determine how much of a threat it may be to soybeans there.

Phillip Sylvester, an Extension agent in Kent County, Del., says the disease showed up for the first time in 2011 in his state. “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 yield losses are likely,” he says.

Determining yield loss from SVNV is going to be difficult because the disease often occurs in combination with other diseases, like cercospora blight. Symptoms from the two diseases and other commonly occurring diseases in soybeans are similar.

Phipps says the new disease was widespread in Virginia last year, though most growers didn’t know it even existed.

“We didn’t see the symptoms expressed until July, and then symptoms became more and more prevalent later in the growing season,” Phipps explains.

Symptoms found in mid-July

The Virginia Tech pathologist says little is known about the infection process. It could be that infections from thrips are occurring early, but the symptoms don’t show up until mid-July.

Whether moving up thrips treatments and intensifying application of these pesticides will affect the disease one way or another isn’t known, Phipps says. If it is like other tospo viruses, tomato spotted will virus, for example, the primary tools for managing it will be seed treatment insecticides or foliar sprays.

Virginia Tech Entomologist Ames Herbert says so little is known about the way thrips vector this new disease it is difficult to know what, when, or if chemical treatment is needed.

“We don’t know what thrips species is transmitting the disease or when this might happen. We do know that thrips alone is not an economic threat to soybeans,” Herbert says.

“Until we know more about the disease and the infection process, I would not go with wholesale protective measures, until we determine the need and the best strategy for managing thrips in soybeans. We could waste a lot of time and money putting out the wrong material and getting little in return,” Herbert says.

If there is good news connected to having a new disease to manage, it is that SVNV is not seed transmitted. It has to have an insect host to vector the disease.

Two relatively new insect imports from China, the brown marmorated stink bug and the kudzu bug, known throughout most of the world as the bean platispid are expected to be prevalent in 2012. Both insects have been bigger problems in other states, but seem destined to meet in Virginia.

The kudzu bug is the first of its entire family ever to be found in the U.S. Nothing even close to it has been found in the U.S., says Virginia Tech Entomologist Ames Herbert.

The brown marmorated stink bug has moved slowly southward from Pennsylvania over the past few years. Last year, for the first time, soybean growers in north and central Virginia had to treat their fields for this pest.

The kudzu bug is approaching Virginia in a steady south to north movement. It was first found in north Georgia, and within two full growing seasons made its way through the Carolinas.

Based on previous south to north migration, it appears certain the kudzu bug will be a problem in Virginia soybean fields this summer.

The good news, Herbert says, is that a joint research project among Maryland, Delaware and Virginia Tech researchers has turned up some good management strategies to manage brown marmorated stink bug. This information is available to growers via their county Extension office or from any of the IPM websites in these states.

The kudzu bug has been a big problem, especially in South Carolina, where it first became a problem on soybeans. Initial research by Clemson Entomologist Jeremy Greene, and subsequent work by North Carolina State entomologists, has provided some answers to managing this pest, and this information will be valuable to Virginia soybean growers as the pest moves northward.

“It is extremely challenging to researchers and even more so for farmers, because we still have to deal with our native insect species. Add to that challenge, these new invasive insects from other parts of the world, and it’s a big challenge.

“And, as the brown marmorated stink bug and kudzu bug have proven, we don’t really know what insect challenges we will be facing in the future,” Herbert says.

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