Farmers in the upper Delta received a “million-dollar” rain Father’s Day weekend. But the rains that provided much-needed moisture for area cotton could also be a boon for some cotton insect pests.

That could be bad news for growers in areas where tarnished plant bugs are showing higher levels of resistance to acephate or Orthene, one of the chemicals of choice for controlling the pests, than they’ve displayed this early in previous years.

“They (plant bugs) are all over wild hosts,” Gus Lorenz, Arkansas Extension entomologist said in an interview on June 20. “Take a sweep net to some of the weeds on the field edges, and plant bug numbers are incredible. In 25 sweeps, I can’t count the number of plant bugs.”

Lorenz and other Mid-South entomologists have been asking growers and consultants to avoid applying acephate prior to bloom to try to forestall the total loss of the organophosphate insecticide against tarnished plant bugs.

But that could be problematic this year because the Mid-South crops appears to be split 50-50 between cotton planted before the cool, wet conditions that hampered planting in early May and that planted after.

“We’ve become way too reliant on that one insecticide,” says Ralph Bagwell, Extension entomology specialist with the LSU AgCenter, speaking to growers at the AgCenter’s Northeast Research Station Field Day on June 14.

Bagwell said growers should begin alternating acephate with other products recommended for tarnished plant bug control. The latter include Centric, Trimax Pro and Intruder, a class of insecticides known as nicotinoids or nicotinyls; Vydate, a carbamate insecticide; and FMC’s new Carbine insecticide, a pyridine carboxamide material.

During the winter meetings, entomologists such as Bagwell and Lorenz; Angus Catchot, Extension cotton and soybean entomologist with Mississippi State University; and Scott Stewart, cotton IPM specialist with the University of Tennessee, urged growers to apply those insecticides prebloom and follow with Orthene and Bidrin after bloom.

“The hope is once we get into bloom we could still get some use out of the organophosphates if we lay off of them early in the season,” said Catchot. “Once we get into bloom and start picking up immatures, we also can start adding Diamond, an insect growth regulator that is gaining in popularity in Mississippi.

“It has activity only on nymphs and can be tank mixed with an adulticide, which will give us another mode of action.”

“Early indications are that we’ve got resistant plant bugs that made it through the winter,” said Lorenz. “That’s the first time we’ve seen that. Usually, over the winter, the resistance level drops. It creeps back up over the course of the growing season.

“This year, however, the resistance carried over. That means levels of resistance have been high even in the spring populations in April and early May. From the start, around Portland up through Grady and Gould, populations were relatively high – with high levels of resistance to both pyrethroids and organophosphates.”

Lorenz said entomologists are concerned that if Orthene becomes ineffective on plant bugs, “we’ll lose Bidrin right behind it. We need to maintain those as long as possible. The best way to do that is to avoid early use of those products.”

“One of our biggest fears is that we’ll see resistance to Centric, Trimax, Orthene or Bidrin,” said Glenn Studebaker, Arkansas Extension entomologist. “We’re not seeing a lot of tolerance in the neonicotinoids like Centric. But in the bio-tests done over the years, higher doses of Orthene and Bidrin are now needed to kill plant bugs.”

Catchot says the development of acephate resistance is a serious issue for the Mid-South.

“In the past, industry has always stepped up with new chemistries, but this is not the case this time,” he said. “There have been very few new chemistries introduced in recent years that equal the ‘standards’ like Orthene and Bidrin. In fact, the chemical companies say there are almost no products in their pipelines to replace the organophosphate chemistry any time in the near future.”

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