Conventional cotton changes insect control

If you’re going to come up with a plan for managing insects in conventional cotton, you need to take a step back in time to the pre-pyrethroid days in 1976, says Auburn University Extension Entomologist Ron Smith.

“In some instances, that’s where we’re at if we’re growing conventional cotton,” says Smith. “If you’ve got a system you like, I’m not trying to change your mind, but based on about 36 years of experience, I’ve got some ideas on how to manage insects in conventional cotton.”

Growers now have better chemistry for worms, but it’s very expensive, he says. “You can’t afford to use it very many times. We need to think like we thought before 1976, when we didn’t have these tools.”

This past year, Smith and other researchers conducted trials at Prattville in central Alabama and Headland in southeast Alabama. A systems trial at Prattville compared Bollgard, Bollgard II, WideStrike and conventional cotton varieties. Some of the conventional varieties were over-sprayed with new worm chemistry, he adds, including Coragen from DuPont and Belt from Bayer. Larger plot tests were conducted in southeast Alabama, where worm pressure traditionally is more severe. In addition to the new products, all chemistries available for treating worms were used. One spray was made in the Prattville test and two were made in Headland.

“In south Alabama, we put Karate in the mix because we wanted to see what a pyrethroid would do against tobacco budworms,” says Smith. “Karate against budworms was no different than the untreated. If you’re going to grow conventional cotton, you’ve got to know if you’re dealing with budworms or bollworms because pyrethroids can’t be used with any success against budworms.

“If you’re dealing with worms in June, it could be budworms. If you’re dealing with worms during the first two weeks of July, it could be budworms. In the last two weeks of July, it’s likely bollworms. In August, it’s likely a mixture. You’ve really got to do a good job of getting the right chemistry out there and avoid hitting the wrong worm species at the wrong time. One shot is all you’ve got, because by the time you see that it’s not going to work, the worms are too big for you to go back and correct the problem.”

Eight days after the second spraying in southeast Alabama, says Smith, the worm chemistry looked good while the cotton treated with a pyrethroid looked the same as the untreated.

Budworm materials are expensive, he says, about $12 to $15 per shot. “Coragen is a great material, but we didn’t know until last season what it would cost. They’re not promoting it in the cotton market, and we were using a $32-per-acre rate — it’s going to the vegetable market. It’s a great material, but I don’t think it will be a factor, so we’re working with Belt.”

Looking at insect control strategies for north, central and south Alabama, Smith says in the southern part of the state he’d put most of his inputs in the latter part of the season because of the increased worm pressure.

“In north Alabama, due to earliness and a plant bug problem, I’d put more of my inputs in the front part of the season to see if I can cut off the expense with maturity. In central Alabama, we’ll treat it like anywhere else. In some years, a foliar spray will help with thrips control and make it look better. With plant bugs and aphids, we’ve got to accept the damage and conserve beneficials and make it until the bollworm window in late July before we pull the trigger with hard chemistry.

“You can’t afford to fight a budworm but for one generation, and I’d fight them in August. We’ve got to minimize the budworm fight — you can win the battle in June or July but you can’t win the war. You’ve to stay under the field when it’s hard chemistry. I like a pyrethroid automatic spray about July 20. Normally, bollworms coming out of corn will overwhelm beneficials. You’ve got stinkbugs coming into the field, and I like an automatic spray because it’s hard to find that population — you’re dealing with white eggs on a white bloom.”

The second spray, if needed and based on scouting, should be made about a week later, says Smith. “If we see some budworms, I would budget one $14 shot sometime in August. Then, I’ll allow for another stink bug spray then. That’s what I’d be shooting for if I was growing conventional cotton in central Alabama.”

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TAGS: Cotton
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