Soybean acres are up in Virginia and so are concerns about two relatively new imported pests, brown marmorated stink bugs and kudzu bugs.

Virginia soybean growers planted about 600,000 acres of soybeans this year, but few imagined prices would be pushing $20 a bushel ($18.39 on the last day of August) by the time they will harvest this year’s crop.

The increased value of this year’s bean crop makes late season insect control all the more imperative.

Neither kudzu bugs nor brown marmorated stink bugs (BMSB) are entirely new to Virginia growers. Last year BMSB infested soybean fields in a relatively small area of the state. They moved into commercial soybean fields early and typically didn’t move far into the fields.

(For an earlier report on the situation, see New insect pests converging on Virginia soybeans).

As a result, Virginia Tech Entomologist and state IPM Leader Ames Herbert helped develop a program that recommended growers spray one-time on the field edges with one of any number of insecticide products.

This limited management tool seemed to work fine last year. This year Herbert says the Asian imports aren’t playing by the rules. We are finding BMSB well into soybean fields and they appear to be coming into commercial fields at slower pace than last year, but also seem to be spreading out over a bigger part of the state, he notes.

This is only the second year these particular stink bugs have been known to infest commercial soybean fields in Virginia. As a result of the short learning curve, researchers and growers alike are being forced to make some of the rules for management for these pests on the run.

The brown marmorated stink bug is a native of Asia, hence its’ common nickname Asian stink bug, and was first found in and around Allentown, Pa. in the early 2000s. It was mostly a problem for homeowners and gardeners for the first few years, but now seems destined to become a major pest of agricultural crops.

BMSB is native to China, Japan, Korea and Taiwan. Since its first occurrence primarily as a household pest in Pennsylvania, BMSB has been reported in over 20 eastern and southern states ranging from Maine to Mississippi, as well as Ohio, California and Oregon.

Entomologists across the country seem to believe the distribution of BMSB is much wider than currently documented and that detections will increase with greater public awareness of this pest.

This insect is a strong flyer and readily hitchhikes on vehicles, thereby contributing to the rapid spread of this pest.

Though similar to its common cousins brown stink bugs, green stink bugs and Southern green stink bugs, the Asian version has some unique and troubling characteristics.

The native stink bugs tend to over-winter in wooded areas in and around agricultural fields. The Asian stink bugs have shown a propensity to over-winter in urban areas, specifically in very high populations in houses, sheds, barns and other structures.

Spreading rapidly

Herbert says this year, his research team has already documented BMSB populations in 20 Virginia counties and the number is almost certain to go up. He contends by the end of the year there will be many more soybean fields reporting BMSB populations than last year.

The Virginia Tech IPM leader says in some cases BMSB are following the same pattern of infesting only the edges of soybean fields. “Many growers are treating field edges this year and we are going to follow as many as possible to determine if those treatments worked and held,” he adds.

“The good news is that based on our insecticide trials it is not difficult to kill BMSB with several common insecticide products. And, many fields, especially the full-season crop fields, are rapidly approaching the safe stage, which based on previous field cage studies happens after R6 (full seed) when pod walls begin to toughen,” he explains.

Kudzu bugs are beginning to become more frequent pests of crops in Virginia, too. This Asian import, entomologists contend is most likely from Japan, is moving rapidly from south to north.

Since it was first confirmed in the U.S. in north Georgia in October of 2009, kudzu bugs have infested every county in North Carolina and South Carolina and are rapidly getting established in southern Virginia.

North Carolina State University Entomologist Dominic Reisig says in general this year many acres in his state were treated for kudzu bugs that didn’t need to be treated.

For sure, kudzu bugs can damage soybeans. In untreated tests we’ve seen up to 50 percent yield loss, but averaged nearly 20 percent across untreated soybeans, he says.

In South Carolina, Clemson Entomologist Jeremy Greene says soybean yield losses of up to 20 percent in untreated fields were seen last year.

This year farmers seem to be keeping a careful watch out for these pests and monitoring various information sources to stay ahead of these bugs, he adds.

There is a website dedicated to kudzu bug monitoring and management (www.kudzubug.org) that has an easy to use population threshold that can be used to determine when to spray. It also has timely updates on movement of kudzu bugs, insecticide control, identification photos and other tips for managing this new pest.

“Kudzu bug is so new and so potentially damaging to crops that growers just don’t know what to do. I had one agent tell me that one of his growers found one adult kudzu bug in a field, and he sprayed the field. That’s one end of the extreme and the other is waiting too late to manage populations of these bugs,” Reisig says.

Virginia soybean growers are caught in the middle of the north to south migration of BMSB and the south to north migration of kudzu bugs.

The increase in soybean acreage and the high price of beans ups the ante on developing economically sound management strategies for controlling these pests.

Neither of the Asian imports appears to be difficult to kill with a number of insecticides.

With BMSB, it is difficult to get accurate threshold numbers because of this insect’s amazing startle reaction. Herbert says sweep nets are still the best option, though sometimes standing in a field and slowly turning 360 degrees and counting the number of bugs you can see works about as well.

Kudzu bugs are likewise not difficult to kill, but when they get into soybeans with heavy foliage, getting the insecticide to the insect can be challenging, because these bugs feed on the underside of leaves and on stems of soybeans.

Scout late season soybeans, then scout them again and again seems to be the universal advice of entomologists across the Southeast as growers struggle to take optimum advantage of this year’s high prices.

rroberson@farmpress.com