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Watch for stink bugs in late soybeans

Watch for stink bugs in late soybeans

Look for stink bugs in late-maturing soybeans. "Wormy" year for Arkansas row crops. Yellowstriped armyworm, bollworm numbers high. Soybean loopers "blanketed" the state.

Favorable weather conditions have allowed soybean harvest to roll right along throughout much of Arkansas. To make matters even better, stink bugs have been relatively light across much of the state.

Brown stink bugs seem to be the primary species found at significant levels, although there are some areas with treatable levels of the larger (and easier to control) green stink bugs.

The most notable observation thus far is the apparent lack of redbanded stink bug, Piezodorus guildinii, in Arkansas soybean. Even southern areas of the state that have experienced building numbers of this pest over the last few years have seen very few, if any, redbandeds thus far.

In fact, it is possible that many of our growers and decision-makers will not see this pest all season. I believe the cold snaps we had this winter may have reduced their numbers significantly. 

However, any late-maturing soybeans remaining should still be scouted into R7 as stink bugs (particularly redbanded) have a tendency to move into fields fast. I currently see several fields that will still be hanging on for the next couple of weeks -- I’d hate to see any late-arriving stink bugs take us by surprise.

Although we may finish the season having escaped stink bugs, we saw our fair share of insect problems in Arkansas soybean. 2010 turned out to be a “wormy year” with extremely high numbers of lepidopteran pests from start to near finish.

Even yellowstriped armyworm, a pest whose numbers rarely justify treatment, were unusually high early on in spots.

We also received many reports of fall armyworm in soybean. This was likely the rice strain that we commonly see in pastures, as we received numerous calls for pastures having reached treatment level of fall armyworm during the same time periods. Many of the treatable levels of fall armyworm resulted from controlling grasses that the worms had been initially feeding with a postemergence herbicide (such as glyphosate).

2010 was also a banner year for bollworms, as we experienced significant numbers in cotton as well as soybean. Pyrethroids applied alone left more larvae in the field than was expected in several cases. Some of these instances may have been due to pyrethroid-resistant tobacco budworm being present but a building tolerance to pyrethroids in bollworm may have also been the culprit. Bollworms are easily the most destructive pests to Arkansas soybean, as significant feeding on pods can occur in a short period of time.

Soybean loopers quite simply blanketed soybeans across Arkansas. We averaged over 200 loopers in 25 sweeps in some areas of southeast Arkansas. The highest I sampled was 340 loopers in 25 sweeps. Needless to say, that is an extremely high number -- over 10X threshold.

Apparently, a virus wiped out many of the soybean loopers in short order. One of my fields averaged 300 loopers in 25 sweeps on August 20.  Five days later, the field averaged 50 loopers. Three days after that, there were zero loopers.

This is why the recommendation to wait until loopers and other caterpillar pests to establish some size before treating can be a wise decision. Natural enemies such as diseases, predators, or parasitoids may step in and do the work for you, thus saving an insecticide application.

Integrated pest management is a highly effective tool in soybean production, and it is often up to us to utilize it to our benefit.

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