Growers warned of acephate resistance

OK. Admit it. How long have you been addicted to spraying acephate to control tarnished plant bugs in your cotton?

It's nothing to be ashamed of. A lot of growers have become overly dependent on relatively cheap, highly effective insecticides, herbicides and other ‘ides at some point in their farming careers.

But Extension entomologists and USDA researchers are warning that unless growers begin weaning themselves from total reliance on acephate or Orthene, it won't be long before they'll be forced to go through withdrawal. And it won't be pretty.

“We've gotten way, way too reliant on that one insecticide,” says Ralph Bagwell, Extension entomology specialist with the Louisiana State University AgCenter. “We need to begin alternating acephate with other insecticides that are recommended for tarnished plant bug control.”

Bagwell, a speaker at the Northeast Research Station Field Day, said tarnished plant bugs have become the No. 1 insect pest in cotton in Louisiana now that Bt cotton has eliminated most insect sprays for tobacco budworms and bollworms.

“Most of the applications that go out now for insect control are geared toward tarnished plant bugs,” he said. “The vast majority of those applications are with one insecticide, acephate. And we are beginning to see significant changes in tarnished plant bug tolerance to acephate.

“You can think about where we were five years ago when we were actually able to control tarnished plant bugs with about one-third pound of acephate versus where we are today,” said Bagwell. “We're putting out three-quarters and even up to a pound of acephate just to try to get significant control.

“If we continue using acephate at these levels, we probably will experience a total loss of acephate for use on tarnished plant bugs.”

He said entomologists in Louisiana and other Mid-South states are working on a series of recommendations aimed at forestalling the total loss of acephate as a reliable material for tarnished plant bug control.

“I think that if we can alternate at least every other application with one of these other insecticides, I think it's going to help forestall the total loss of acephate. So we are strongly recommending the rotation of different insecticides. And there are quite a few of those that are recommended for tarnished plant bug control.”

University of Arkansas entomologists are advising growers to stick with the neonicotinoid insecticides such as Centric and Trimax or Vydate, a carbamate insecticide, which also has activity on nematodes, on pre-bloom cotton.

“The neonicotinoids should be used pre-bloom,” says Gus Lorenz, Arkansas Extension entomologist. “Once the crop kicks over to bloom we should switch to Bidrin or Orthene. That's to avoid resistance buildup to Orthene.”

University of Tennessee entomologists have also implemented new insect resistance management plans for plant bugs in their cotton insect control recommendations.

“Essentially, we have a window approach and are discouraging the use of Orthene, Bidrin, other organophosphate insecticides and pyrethroids from first square to first bloom,” says Scott Stewart, cotton IPM specialist based at the West Tennessee Experiment Station in Jackson.

UT recommendations call for the use of Intruder, Carbine, Trimax Pro, Trimax or Centric in the pre-bloom window. Growers can choose between Orthene, Lorsban, Bidrin, dimethoate, malathion, Diamond, Vydate or pyrethroids in the bloom window.

The next step for forestalling resistance involves changes in carrier volumes.

“The more water you put out, the better control we find,” said Bagwell. “So we generally recommend higher volumes of water. “If you're going out with 3 gallons of water and up the volume to 10 gallons, you're going to see a fairly significant difference in control.

“Same thing with an airplane. We've been able to document differences between 1 gallon and 5 gallons of water. So the more water you put out, the better the control.”

Spray tips are another area of concern, he said. With the number of Roundup Ready crops being planted, farmers have been shifting to low-drift spray tips to lessen the potential for putting glyphosate on non-target crops.

“Low-drift tips are great for reducing the herbicide drift, but insecticides kind of need a little drift,” he said. “The more atomization of the actual droplets of the insecticides the more coverage and the better control you're going to get with those products.”

Bagwell handed out the results of a study by Roger Leonard, professor of entomology with the LSU AgCenter's Macon Ridge Branch Station, and Jeff Gore, research entomologist with USDA-ARS at Stoneville, Miss., on the use of air induction and hollow cone spray nozzles.

“When they tested air induction or low-drift tips against hollow cone tips, there was always a significant increase in the percent control associated with the use of hollow cone tips,” Bagwell noted. “So if you're going out by ground we strongly recommend the use of hollow cone tips.”

Lorenz said he's concerned that if acephate or Orthene becomes ineffective against plant bugs, Bidrin faces a similar fate.

“These are our stoppers, the ones we use to get out of trouble,” he said. “We need to maintain those as long as possible. The best way to do that is to avoid early use of those products. That's why we should stick with the neonicotinoids or Vydate until bloom, when we really need them.

“We're trying to impress that tarnished plant bugs are more problematic mid-season from bloom to boll-set. We get more damage and loss from bloom than pre-bloom.”

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