Armywormageddon: That’s the term Angus Catchot has coined this year for what he says is “by far been the biggest armyworm invasion we’ve ever seen in the Mid-South.”
And the worm influx isn’t crop specific, he said at the joint annual meeting of the Mississippi Boll Weevil Management Corporation and the Mississippi Farm Bureau Federation Cotton Policy Committee.
“They’re in bermudagrass pastures, rice, corn, cotton, soybeans, milo — it doesn’t matter; we’ve sprayed them in every crop. They’re bad, and they’ve been coming since the beginning of May. These armyworms are the rice strain, or grass strain. They come to grass, kill the grass, and then move off to eat your crops.”
There is one difference for this year’s invasion, says Catchot, who is Extension entomology professor at Mississippi State University. “We’ve never before seen the grass strain hurt Bollgard II cotton; they’ve never eaten so much as a hole in a cotton leaf in the past. The standard advice, here and in other cotton states, was that if they’re in soybeans, corn, whatever, you’ve got to treat them if numbers are high, but if they’re in two-gene cotton, don’t worry about them.
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“But that’s not the case this year — in one cotton field we looked at, they caused extensive damage. Ernie Flint, regional Extension specialist at Kosciusko, texted me that one of his growers had to spray for the worms. I went and looked at the field, and the armyworms had hurt the cotton badly in a short period of time.
“It was small, six-node Bollgard II cotton, and they weren’t eating the leaves — they were eating the stems and cutting the plants off like cutworms. In bigger cotton, they were chewing the terminal out of the plants about five nodes down. But that cotton will be OK; it will branch out.
I’m no longer taking for granted that armyworms won’t hurt Bollgard II cotton,” Catchot says, “and I’m recommending spraying if numbers are high. I don’t know if something has changed with this pest, but we’ve never seen this strain hurt cotton before.
“No matter what crop you have, if there is grass in it, and you’re going to make an application of Roundup or other herbicide, if you see armyworms in that grass, you can solve the problem easily — just tank mix a pyrethroid with the herbicide. The worms are easy to kill, and you can save yourself a tremendous amount of heartache by doing this. They’re not like the corn strain, they’re very sensitive to pyrethroids, and they’re super easy to control with low to mid-rates of pyrethroids.”
Although he doesn’t work with rice, Catchot says the armyworms “have been wearing out some rice. Dr. Jeff Gore, research and Extension entomologist at the Delta Branch Research and Experiment Station at Stoneville, has had numerous calls for armyworms in rice this year.”
Plant bugs in cotton
Early July was “a turning point” for plant bugs in cotton, he says. “Plant bugs are with us every year, particularly in the Delta, but until July they had been only light to moderate. Then we started to see a big influx of plant bugs that we usually would see a few weeks earlier in a ‘normal’ year.
“We had been making applications, but instead of spraying 2X or 3X thresholds, we were treating normal threshold numbers. Recently, though, those numbers have picked up dramatically in some areas. In the next few weeks, I’m expecting we’ll have to tighten the belt in some situations.”
There are some areas where square retention is dropping, Catchot says, “and it seems we’re not getting control. With a lot of adults moving into the fields, we’re having to tighten intervals. So far, this has been the exception rather than the rule. We have some areas of the state where we are now having to spray on four- to five-day intervals. You don’t have to do this for long — maybe a couple of times — but you’ve got to tighten intervals when these heavy numbers come in. So, watch your square retention until you get into bloom.”
It’s “very, very difficult” to evaluate how a chemistry is working with plant bugs, he says. “If you’ve got adult plant bugs moving into a field, and you walk through the field a few days after an application and find the same numbers, or higher numbers than before the application was made, the inclination is to think it’s a control failure. But if square retention is maintained, that’s not the case.
“If square retention is decreasing, then you probably need to move to another chemistry. But it’s very, very difficult to monitor the efficacy of any of these chemistries on adult plant bugs, because they’re steadily moving into the fields.
“In some places, next to corn, treelines, or Group IV flowering soybeans, they’re a real problem — it just depends on where you are. But keep in mind that if you get into this situation, you need to tighten your intervals. Once cotton starts blooming, I don’t mind using OPs and mixtures.”
In the Delta area, Catchot says, “I’m not really a fan of using any product alone, particularly when cotton is blooming. Rather, I’d be looking at mixing these products, particularly with bifenthrin or pyrethroids — I think you get much more bang for your buck. I’d like to see more mixes with all products in heavy infestations.”
Resistance in spider mites
Going into July, he says, “It has been a fairly light year for spider mites. We actually started spraying more in the hills than in the Delta. The rains gave us a bit of a reprieve, but we started to see more applications going out in July.”
A warning about spider mites, Catchot says: “We know that there is resistance of this pest to abamectin in Mississippi and Louisiana. Failures and resistance have already been documented in Louisiana this year, and we documented it in Mississippi last year. While abamectin is by far the cheapest product for spider mites, and it’s what everyone gravitates to, there are other options.
“Our recommended rate for all the generics, the EC 1.5 percent loaded formulations, is 10 ounces to 12 ounces. But, for Syngenta’s SC formulation, it’s 2.1 to 2.6 ounces, so be sure you know which formulation you’re using.”
In 2006, when the abamectin products first came out, Catchot says, “we were using only a 4 ounce rate — now, we’re up to 10 or 12 ounces. If you have a failure with abamectin, do not spray it again. Last year, we had people who had failures, and they went back with it, and then went back again with failures each time. Don’t do that.
“You have other choices. Portal, a Nichino product, at 1 pint, is a great option. Zeal, a Valent product, looks really good at 2/3 ounce to 1 ounce, and Oberon by Bayer is a good choice, if it’s available. These will cost more, but if you have an abamectin failure, use one of these instead of repeating the abamectin application.
“I wouldn’t be afraid to start treating with abamectin at a high rate, but if you have a failure, switch to something else quickly. Switch off quickly anyway if you have to come back a few weeks later because that population will have been selected possibly for abamectin resistance from the earlier application and likelihood of control failures will increase after the first application."