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Insect threat receding

STAR CITY, Ark. — Insects were, and still are, abundant in soybeans and cotton this year. But the growing season is almost over, and farmers will soon be able to leave that worry behind.

"We're seeing a lot of stink bugs, loopers, corn earworms and salt marsh caterpillars in Group 5 soybeans," said Chad Norton, Lincoln County agent with the University of Arkansas Cooperative Extension Service.

"A lot of our acreage is to the stage that farmers don't care. Insects aren't hurting yields at this point, although stink bugs can still hurt us quality-wise."

Norton said stink bugs infested early-maturing Group 4 soybean fields earlier in the season, and farmers had to treat some fields.

"Right now, we're so close to being done with the crop that farmers aren't going to make any blanket insecticide treatments. Soybeans are going to start shedding leaves soon, and if the insects want to eat those leaves, it's not going to hurt anything."

Meanwhile, the cotton crop is at various stages of development with some ready for picking. Farmers have just terminated irrigation in other fields, according to Norton.

"We're getting toward the end of the year, and producers will terminate insecticide applications soon unless we get a big flight of beet armyworms in."

The Lincoln County situation is a microcosm of the situation across southeast Arkansas, says Jeremy Greene, Extension entomologist at Monticello, Ark.

He said the Group 4 soybeans were a "good nursery" for the stink bugs infesting the Group 5s now.

Greene said, "We've kept a close eye on stink bugs this year, and they've been pretty big in soybeans and cotton. There are more stink bugs this year than last year in those crops. We had recurring rainfall patterns last year, and stink bugs had an abundance of wild, alternate host plants. A few weeks ago, we lost a lot of alternate host plants, and we had a lot of stink bug movement into irrigated cotton fields."

There are more than 200 species of stink bugs in North America, but in soybeans and cotton, only a few species are economically important. Those include the green stink bug, the brown stink bug and the southern green stink bug. They account for about 90 to 95 percent of the mischief in soybeans and cotton.

Greene urged cotton farmers to monitor insect populations if they haven't defoliated yet. He said stink bugs can cause injury, yield loss and quality reduction if left to feed on bolls with less than 450 to 500 heat units accumulation after "cutout." He says he's seen some fields lose 200 to 300 pounds of lint an acre because of stink bug injury.

Greene said insecticide treatments can cost farmers about $6 to $10 an acre for materials and aerial application. He said generic pyrethroids and organophosphates are becoming more widely available and can help reduce costs.

"Since a lot of cotton is being defoliated, the insect problem is almost over. However, often when the defoliation applications are made, we see a lot of movement from adults leaving the area for adjacent cotton or soybean fields that might not be mature."

Lamar James is an Extension communications specialist with the University of Arkansas.

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