Second in a series of video from the 2021 University of Arkansas Cotton and Rice Field Day

After battling cotton insects for most of the growing season, the last thing farmers want to see is cotton bollworms showing up in their fields after they have made what they had hoped would be their last insecticide application for the pest.

But that doesn’t mean that growers need to get out the spray rig or call their aerial applicator to give the bollworms another shot of what is often an expensive product, according to cotton entomologists in Arkansas and other southeast states.

“We never saw a gain in enough yield to justify the cost of control if we continued to spray after 350 heat units (past nodes above white flower five,)” said Ray Benson, Extension Staff Chairman in Mississippi County, Arkansas, a speaker at the University of Arkansas System Division of Agriculture virtual Corn and Cotton Field Day.

“We would see damage. (Dr. Phil) Tugwell talked about phantom damage, damage on fruit that we’re not going to harvest,” he said, referring to the late University of Arkansas research entomologist. “It looks bad, and it will make you second-guess, but the rules hold up.”

See more: Heat units help can determine usefulness of pest treatment

“Now, you did a lot of fields and some you sprayed one additional time after 350 heat units, and some you sprayed two times,” said Dr. Bill Robertson, Extension cotton agronomist with the University of Arkansas, who appeared with Benson in the presentation. “Did you ever spray any three times?”

Yes,” said Benson.

“I’ve heard Gus (Dr. Gus Lorenz, Extension entomologist with the University of Arkansas) talk about when they first started this research, walking into a field and seeing big old worm hineys sticking up in the top of the plants, and it made his heart stop beating,” said Robertson, and thinking “maybe we cost this grower some money. But those are the phantom bolls. How did yields turn out on those?”

No gain in yield

“We did this, in one season, over 19 fields in the state,” said Benson. “And we only asked for fields that would be challenging, that had a lot of insect pressure. Then people replicated this in other states. We never gained enough yield to pay for an application.”

“And, in some of those, even with the damage in the phantom bolls at the top, they still produced more cotton than the fields you sprayed two or three more times, right?” asked Robertson.

“It was not uncommon that that happened,” said Benson.

“So you have to have faith in the data and try not to second guess yourself,” said Robertson, “because it does make you nervous when you come out here, and your farmer sees worms in those bolls and wants to fire you on the spot?”

“It’s tough to stick to it sometimes when you see it,” said Benson.

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