Virginia cotton insect pests evolving

From a Virginia perspective, thrips, plant bugs, stink bugs and the European corn borer are getting the most attention from cotton farmers these days.

Ames Herbert, Virginia Tech Extension entomologist, presented 2004 research at the annual Southeast Cotton Conference recently in Rocky Mount, N.C.

In regard to thrips, they were plentiful in numbers last year. “But that’s a pest we can control with available pesticides,” Herbert told a group of farmers at the annual conference sponsored by the Southeast Farm Press.

“Overall we had a 341-pound difference between our treated and non-treated plots,” Herbert said.

In four trials, Herbert used Gaucho Grande, Cruiser, Orthene 97 and Temik with an over-spray of Orthene at the first true-leaf stage. “All of the treatments did well,” Herbert says. “The materials flipped back and forth as to the most effective control. With thrips, you basically have three options and they all do a good job.

“Temik is the only option that will give you nematode control,” Herbert says. “All of our work was done with a peanut rotation. If you have cotton with a peanut rotation, you basically have minimized the nematode problems.”

In addition to the in-furrow applications, Herbert also looked at foliar applications for the control of thrips. “It’s hard to beat Orthene as a foliar spray for thrips.”

While thrips are an annual headache for cotton growers, the European corn borer has caused concern only in the last couple of years.

“When we began to see this problem two years ago, we thought we were seeing damping off,” Herbert says. “What we’re finding here is the European corn borer coming into seedling cotton. They bore into the stem or the tip — any place they can find a place to bore into the plant. If that happens, the plant is gone.”

Herbert and Joel Faircloth documented a 10-percent stand loss in 2004 in farmer fields due to the ECB. “Some of the cotton was Bollgard,” Herbert says. Fields with weed problems, especially curly dock, also had ECB damage. “We want to evaluate some of the insect resistant cotton to see if there’s a difference in susceptibility.”

As transgenic cotton has replaced conventional in farmer fields, caterpillars have been replaced by the plant bug, stink bug complex.

As part of a continuing multi-state study, Herbert and his colleagues have been surveying farmer fields for the past three years. In Virginia, Herbert looked weekly at 18 fields in three counties, taking square retention, bloom and damaged boll ratings.

While boll damage averaged 22 percent in the fields, record yields last year didn’t reflect those numbers.

“We had as much as 50 percent damage in untreated and treated plots and no difference in yield,” Herbert says. “2004 was extremely forgiving, a lot of these plants may have been able to compensate.”

In fields that had boll damage, a treatment of Bidrin resulted in a 34-pound difference when compared to non-treatment. “We’re not quite sure what that means in relation to 2004.

“We’re going to have to find a better way to determine whether a field needs to be treated for plant bugs and stink bugs or not,” Herbert says.

The researchers are using sweep nets and drop cloths, but may be arriving in the field at times when the plant bugs have flown away for a brief time.

e-mail: [email protected]

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