Stink bugs are the leading pest in Louisiana soybeans and becoming a much worse problem in neighboring states. The emergence of the red-banded species has caused “our agricultural economists to budget three insecticide applications in early-planted soybeans,” said Roger Leonard, LSU AgCenter entomologist, at the recent Tri-State Soybean Forum held in Oak Grove, La. “In late-planted systems — such as a double-crop behind wheat — five insecticide applications are budgeted.”
The severity of damage the stink bug can inflict should not be underestimated. In many cases, if a grower skips or mistimes an application against an active infestation, he “may not have any beans to harvest. And if he does, the damage can be so extensive the elevator won't take them.”
Compared to its close relatives, the red-banded species appears to be a more serious soybean pest. “The Southern green and green species of stink bugs have been very easy to control with pyrethroids at $3 or $4 per acre. The brown stink bugs are a bit more difficult to control, but a number of products can do a good job on them.
“It's the red-banded stink bug that is much more difficult to control. Most pyrethroids used at high rates don't provide consistent, effective control. It's important to know the differences between the stink bug species because of differences in product efficacy.”
Angus Catchot, Mississippi Extension entomologist, “looked at the activity of a number of products on very high levels of Southern green stink bugs — 60 to 80 per 25 sweeps. All pyrethroids worked very well.”
When the same products are tried in Louisiana, “we essentially take out the greens, do a fair to good job on the browns but leave the red-banded stink bugs. Usually we end up using a combination of products at very high rates. In season-long tests, we find that unless you're using such product combinations on a consistent, sequential basis, you won't hold (red-banded) populations below economically damaging levels.”
In 2008, a new pyrethroid (bifenthrin) obtained registration in soybeans. When this chemistry was used at “the highest labeled rate, we were able to manage the red-banded species and it allowed rotations with the (other product) combinations.
“If you have to use a pyrethroid to control another pest in soybeans (while) red-banded stink bugs are present — and it's rare to treat for only one pest — it is a good idea to consider adding Orthene to improve control above the pyrethroid alone. That works as well as anything else. Another option is to use the combination product, Endigo, which has also performed very well in most of our tests.”
There is some confusion about the identity of the red-banded stink bug. This pest is a cousin to, and often with, the red-shouldered stink bug, another species occasionally found in soybeans.
“Let me be clear: the red-shouldered stink bug is different, although it looks very similar to the red-banded species with a red, grey or black line across its back. Flip it over, and (there is) a spine that runs from the abdomen and between the two pairs of hind legs.
“That distinguishes it as the red-shouldered species. Most consultants know this difference and use it for species identification.”
In 2007, nearly 60 percent of the stink bugs Leonard and his Louisiana colleagues collected were red-banded. A similar survey in 2008 indicated the seasonal population was 69 percent.
The red-banded first became a problem in 2000 in southernmost Louisiana. Since then, it has migrated through the entire state and it's now in every soybean production parish.
It hasn't stopped traveling, with the highest infestations typically occurring in the rice belt of Texas, throughout Louisiana and a small area in central Mississippi. The entire band of counties in southern Arkansas is now beginning to see populations. The red-banded has been identified as a pest in most Southern states.
“You need to be aware of its potential if you haven't experienced this pest. One question we get from growers is: how do you know it's in your field? If you've sprayed for Southern green stink bugs, return to sample the field and still find stink bugs with a band across the back, then you likely have the red-banded as a pest.”
To determine when growers can quit spraying soybeans for stink bugs, Mid-South researchers have begun an insecticide termination study. This work recognizes two important components: yield and quality.
“Most farmers have experienced some problems with seed quality over the last few years. Part of that loss in quality is associated with insect injury to seeds.
“We have found significant yield losses unless treatments continue in the presence of insects through the R6 growth stages. If you want to manage for optimum seed quality, treatments must go through the R7 stage. … Soybeans mature at R8. So at R7, at least one pod per plant is brown and the plants are beginning to senesce.”