Burning down the green bridge that gives insect pests a path to move from winter hosts to cotton plants may reduce in-season insecticide sprayings significantly and could protect seedling cotton from early damage, says an Arkansas State University Extension entomologist.

Scott Stewart told a group of cotton consultants during the recent Beltwide Cotton Conferences in New Orleans that timing preplant burndown weed control is critical to minimize early season insect problems.

“Controlling weeds in areas around the field and along ditch banks is also critical,” he said during the annual Cotton Consultant’s Conference segment of the Beltwide. “Such pests as the tarnished plant bug have a huge host range,” Stewart said. “Hosts include henbit and just about every cotton field has henbit. Spider mites also like henbit and that weed can be a part of the green bridge.”

Stewart said the green bridge is vegetation that harbors insect pests that move into cotton.

“We’ve seen a lot of changes in cotton insect control over the past few years,” he said. “Bt cotton, the boll weevil eradication program and crop rotation have changed the way we manage pests.” He said rotation to other crops, such as corn, may provide alternative hosts for sucking bugs and other insect pests.

No-till and reduced-till systems also affect pest survival. “A lot of areas have to use reduced-till to improve conservation, improve production and boost the bottom line, but farmers need to be aware of the effect on insects.”

He said some pests thrive in reduced-till systems. Cutworms, slugs, false chinch bugs and aphids, among others, may find favorable conditions in reduced-till fields. “A good burndown herbicide helps remove the green bridge that allows cutworms to move from one host to another,” he said.

Slug problems “may be exclusive to no-till. False chinch bugs can also cause problems. Late weed control is a factor” in pest survival.

Stewart said thrips numbers may be reduced in no-till systems because of the cooler soil temperatures. But under the right conditions he said farmers can “get a double whammy with thrips and diseases.”

He said aphids can be more numerous in no-till situations, along with fire ants. Plant bugs and spider mites also may be present in higher numbers in no-till or reduced-till systems.

Stewart said control measures in the Mid-South may include “area-wide plant bug management. If we treat ditch banks early enough, along with in-field burndown applications, we can reduce in-season plant bug treatments. This approach will not fit all farms, especially those with small fields scattered over several miles.” Concentrations of CRP acreage also make this approach more difficult.

He said the economic effect of a timely burndown herbicide application may include one or two fewer in-season plant bug treatments. “Farmers could save almost $6 per acre. We’re trying to make growers aware of the need for timely burndown herbicide applications.”

He said controlling all broadleaf weeds at least 21 days before planting is the goal. “To do that, we need to apply a burndown herbicide four to six weeks earlier. Also, pests are mobile so we have to do outside-the-field management and be aware of pest movements.

“If we don’t get these burndown herbicides out in time we reduce our insect control options and we may have to add an insecticide application at planting time.”

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