Since the turn of the century, red-banded stink bugs have rapidly become the most significant pest in Louisiana soybeans. Might that designation spread to neighboring states?
In 2007, when Scott Akin first arrived at the University of Arkansas-Monticello, he was warned about the emergence of the red-banded stink bug.
“I contacted Roger Leonard (LSU AgCenter entomologist — see http://deltafarmpress.com/soybeans/stink-bug-0130/ for more information) and he showed me some astounding data on how fast the red-banded stink bugs had spread from south Louisiana to the north. The Louisiana situation is scary. In 2007, the red-banded stink bug was close to 60 percent of the species composition in Louisiana surveys. When I first saw that figure, it was hardly believable. I asked Leonard, ‘Is that right? Sixty percent?’ But it was true.”
Amazingly, 2008 Louisiana surveys showed the red-banded stink bug percentage had jumped to almost 70 percent.
With such data, “I figured it would be prudent to study up on the red-banded stink bug so we'd be ready for it in southeast Arkansas. Since then, it's interesting that the red-banded stink bug hasn't yet zoomed into our state like some feared — but the threat certainly remains.
“So far, the red-banded stink bug tends to show up late in late-maturing southeast Arkansas beans. They can show up in high numbers, but it remains to be seen if they do a lot of widespread damage late in the year. Without further study, though, it's hard to say anything definitive regarding damage to our crop.”
Akin now has a graduate student working on red-banded stink bugs. He's looking at damage potential of the red-banded stink bug compared to the Southern green stink bug along with control options.
“We have sufficient information about the Southern green stink bug with respect to damage and control. If we can see how this new stink bug compares, it'll help us understand how seriously to take it — especially if it takes off here like it has in Louisiana.”
In 2007, “I first saw some red-banded stink bugs in Desha County in late July. There were several in one of our bollworm trials in soybean. Then, they showed up big in Ashley County in October.”
Before explaining the Ashley County field, it's good to know that in 2007 there were far fewer double-crop soybean acres than in 2008. In 2008, the state had nearly 1 million acres of wheat, resulting in many double-crop soybean fields.
Last spring, with so many wheat-bean acres projected, “I heard a lot of, ‘Boy, stink bugs are going to be awful in our late beans.’ That may not necessarily apply, though. With the increase in late-maturing acreage, I don't believe the stink bugs had the opportunity to gang up on isolated fields as in the past. Still, they were out there and required some sprays.”
Farmer fears stemmed from all stink bug species being highly mobile and highly selective. Late in the season, the pest can readily move to the greenest field available once fields they're in dry down or are harvested.
“They'll almost flood into it and, when that field plays out, they'll move into the greenest nearby field until there are no more fields in the area to travel to.”
That's what happened in the Ashley County field in 2007, when Akin received a call from Extension agent Gus Wilson. With almost 200 stink bugs per 25 sweeps, Wilson's concerns were obvious. Of that sweep count total, 42 of the stink bugs were red-banded. The unofficial Louisiana threshold for red-banded stink bugs is six per 25 sweeps. In Arkansas, the threshold for Southern greens, greens and browns is nine per 25 sweeps.
The Ashley County beans were a late-planted, late-maturing variety that was well irrigated throughout the season. The field was at R-7 when the stink bugs were discovered.
At the same time, “the grower had hit his limit in spending on the crop with fungicides and the like. The problem, of course, is that although stink bugs may not have the same damage potential as bollworms, they can still hurt the yield and quality, even at R-7. The field, which had significantly more yield potential, ended up averaging 19 bushels per acre. They were hit hard.”
One of the biggest challenges with red-banded stink bugs is proper identification.
“Folks who don't deal with stink bugs regularly find it difficult to tell the red-banded stink bug from other stink bugs — especially the red-shouldered stink bug (which doesn't cause nearly the damage to a soybean crop and is easier to control). The red-shouldered stink bug has been in Arkansas for a while, although at relatively low numbers.”
Typically, when doing sweep counts, all stink bugs are counted together.
“The red-shouldered are often included with the Southern green and green stink bug species. Of course, the Southern greens and greens are separate species, but we lump them together for threshold decisions since control options are the same for both.”
One way to differentiate the red-banded stink bug: a fixed spine on the bottom side that runs from the abdominal section upward between the hind legs.
However, sometimes even the spine can be a difficult characteristic to go by. “Sometimes the spine can be somewhat translucent and if it's hot outside and you're sweeping — 90-plus degrees and sweat dripping in your eyes — it can be hard to see. That said, I've had new student workers who can recognize slight differences in overall body shape and texture within just a couple of hours working with both of these pests, even from fair distances. I'm hoping that if red-banded stink bugs become a significant pest, decision-makers can have as much ease in differentiating them from the red-shouldered stink bugs. Even so, the nymphs are much easier to tell apart.”
As for control of red-banded stink bugs, Endigo (a mixture of Centric and Karate), which was fully labeled in soybean last spring, is one of the top products Akin recommends. “Using 4.5 ounces per acre has worked well in our trials. Acephate products at higher labeled rates have looked good in trials, as well.”
Akin points to bollworms and loopers as the most problematic pests for southeast Arkansas soybeans in 2008.
“Bollworms attack blooms and all stages of pods and can really take the legs out from under a crop quickly. Last year, some fields in southeast Arkansas received two or three applications for bollworms. I think the increased amount of corn acreage may be having a profound effect on bollworm populations in our state.”
South of I-40, loopers were a big problem in some fields. “Actually, I believe we had some mixed populations of soybean loopers and cabbage loopers. We saw the same in our southeast Arkansas trials. Some of the data we collected this year showed suppression by pyrethroids. With soybean loopers often being flared by pyrethroids and cabbage loopers historically being controlled by pyrethroids, the suppression we saw in our trials suggests that we likely had mixed populations of both.”
When he first arrived in the state, Akin says, a common comment at grower meetings was, “‘I've noticed acephate isn't in your recommendations (Arkansas MP-144) for soybean loopers. But I used a half-pound of it and got good control.’
“I think the success they had achieved may have been due to them having more cabbage loopers than soybean loopers. The cabbage looper is much easier to kill.”
To see if that's the case, this year “we plan to collect larvae in our trials to rear to adulthood to confirm species composition. The black-leg versus green-leg key for identification is not always 100 percent. And making a pyrethroid application or too low a rate of Intrepid on a soybean looper population could be a big mistake. Treatment recommendations will depend on what we find.”