What is in this article?:
- Bollworms increasingly a problem in Mississippi soybeans
- Bollworms harder to control
- Grain sorghum headworm complex
“We sprayed almost no bollworms in Mississippi soybeans until 2006," says Angus Catchot, associate Extension professor of entomology and plant pathology at Mississippi State University. "But now we’re on an incline where we’re spraying more and more — last year we treated around 750,000 acres an average of two times. The acreage is growing every year, and we’re seeing more pyrethroid-resistant bollworms.”
KEITH GRIFFIN, from left, Chemtura AgroSolutions, Orlando, Fla.; Dave Cummins, Bayer CropScience, Madison, Miss.; and Manley Gilliam, also with Chemtura, Santa Rosa Beach, Fla., were among those attending the Mississippi Agricultural Consultants Association annual meeting.
Grain sorghum headworm complex
Although grain sorghum acreage in Mississippi was small last year, only about 50,00 acres, he says, “It seems we got calls on every field for the headworm complex, mostly bollworms.
“I do a lot of grain sorghum tests every year, as does Jeff Gore, assistant research professor at the Delta Research and Extension Center, and we’ve seen basically 50 percent control of bollworms. Every year, in our tests, we’ve been seeing control slipping further in grain sorghum.
“There are a couple of options: Lannate, which has been a standard, and Belt, which was only recently labeled for grain sorghum. A lot of Belt was used last year; it worked extremely well in soybeans and pretty well in grain sorghum, although it didn’t get us below threshold in a lot of situations. I don’t know why. For the most part, it did a pretty good job in grain sorghum, but it wasn’t the slam dunk that it was in soybeans.
“In years like 2011, with the kind of pressure we had with the headworm complex, particularly bollworms, I don’t know that we necessarily have a slam dunk option. If you have a tight head sorghum variety, you won’t get the control you get with a loose head variety, simply because of the coverage factor.
“One of things I tried last year in grain sorghum tests was to apply a residual such as Belt when making a midge shot with a pyrethroid, thus saving on application cost and aiming for residual control of bollworm eggs that hatched five to seven days after the midge application.
“It actually worked very well and definitely looked better than applying Belt on established threshold populations of large worms. We will look at this further. The downside of this system is that you’re assuming you’re going to have a worm problem, so you may be applying an expensive product to control a problem that may not occur.”
Pyrethroids continue to provide “decent control” of bollworms in Bollgard II cotton, Catchot says, “because we’re still targeting very small worms and hatching eggs of worms already weakened from the Bt, whereas in other crops such as soybeans and grain sorghum we’re often going after worms that already have attained some size, which compounds the control problem.
“Typically, in the Mid-South, pyrethroids are being co-applied with organophosphates for plant bug control, which also corresponds with hatching bollworm eggs. The tact is that if the pyrethroids ever stop working in cotton, we probably will have to start spraying the more expensive materials on a crop where we’re already paying a tech fee for lepidopterous pests.
“But data from Ryan Jackson, Gus Lorenz, Roger Leonard, Philip Roberts, and Scott Stewart suggest that growers may be leaving money on the table by not stepping up their worm control programs in Bollgard II and Widestrike cotton varieties. Yield increases, using two applications of Prevathon or Coragen — one about the third week of squaring, the second three weeks later — have ranged from 150 to 350 lbs.
“You might get some flak from your growers about over-treating, but these data show very clearly that there are situations where additional control measures are needed to maximize yield in these two gene varieties,” Catchot says. “Currently, our research efforts are going to focus more on identifying exactly when those situations exist.”