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Toasts insects at same time: Field oven cooks up defoliation alternative

Baking cotton plants with blasts of air at 250 to 350 degrees Fahrenheit could provide a fast-acting alternative to traditional defoliants that has the added benefit of toasting insects responsible for sticky, hard-to-clean cotton.

The heat treatment recipe, developed by scientists with the U.S. Department of Agriculture's Southwestern Cotton Ginning Research Laboratory in Mesilla Park, N.M., calls for a tractor-pulled oven with an enclosed propane burner and motor-driven fan.

A one-row prototype has served up rows of crisp, brown cotton leaves in New Mexico, West Texas and California fields. Heat treatment produces faster results than traditional defoliants, which take up to two weeks to act.

“The cotton leaf is two cells thick, so this process cooks the leaves within 24 hours,” says Paul Funk, an agricultural engineer with the Agricultural Research Service lab on the New Mexico State University campus.

The facility is one of three in the nation along with USDA labs in Stoneville, Miss., and Lubbock, Texas and the only one with a focus on irrigated, long-staple cottons grown in the West.

This fall, crews harvested Acala and Deltapine cotton at NMSU's Leyendecker Plant Science Research Center to pinpoint an optimal temperature for heat treatment. Control plots were treated with conventional defoliants that allow farmers to harvest the highest percentage of mature cotton in a single pass through the field.

Defoliants stop leaf growth, open bolls and cause leaves to drop from the plants before harvest.

Heat treatment, in contrast, leaves foliage on plants, so scientists need to ensure that gins can get the fiber as clean as cotton from defoliated fields.

To find out, they ran seed cotton from heat-treated rows at Leyendecker through the ginning lab to compare it with fiber from defoliated plots.

“Through our partnership with textile researchers in the Cotton Quality Research Unit at Clemson University, we can follow the fiber all the way from the field through the spinning process,” says Carlos Armijo, research textile technologist with the local lab.

“We'll be able to provide comprehensive information about the fiber and find out whether heat treatment has affected the cotton's properties.”

If heat-treated cotton passes muster in gins and textile mills, it could help solve a sticky problem of conventional defoliation. Defoliant-treated cotton seems to attract sucking insects that secrete a gluey waste that can turn black and moldy, matting the fiber.

“People in the industry refer to it as sticky cotton,” Funk says. “It's difficult to gin, and you cannot spin the fiber if there's too much stickiness. But the heat kills the aphids and whiteflies that live on the undersides of leaves.”

Heat treatment also is an option for long-staple Pima cottons, which are difficult to defoliate chemically, he says. “Organic growers don't have any tools in their box for defoliation,” Funk adds.

Because no crop dusters are used, heat treatment can be done on windy days. “We've tried it ourselves when we were too stubborn to wait, and wind didn't dissipate the heat,” Funk says.

For further tests, scientists hope to develop a full-scale prototype capable of treating four to six rows at a time.

“The cost per acre is roughly equal between propane and defoliant, but the ground rig is more expensive to operate because of labor costs,” Funk says. “A self-propelled machine could be the next step if it's feasible and economical.”

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