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Corn+Soybean Digest

Relaying Insect Control

Running “relay” crops beside cotton can help it win the race against insects.

Coupling that practice with planting cotton into a wheat cover crop can help increase yields by two- or threefold over other cropping systems, says Texas A&M entomologist Jeff Slosser.

Slosser and his associates are looking at new ways to use biological control to prevent insect damage to cotton. In intercropping field studies at the Texas A&M Ag Research and Extension Center in Vernon, three crops are planted in strips on land destined for a cotton crop the next growing season.

“These crops provide a winter and spring home for beneficial insects that will later move into our summer cotton and help reduce populations of cotton pests,” says Slosser.

Native predators and parasites are often highly effective against aphids, bollworms, beet armyworms, tobacco budworms, whiteflies and other pests that attack cotton.

The relay crops include vetch, a legume normally planted in fall; canola, planted in late winter; and grain sorghum, planted in late March. They're planted in four-row widths, separated by 44 rows of cotton planted in 40" rows. All relay crops are killed once they begin to mature.

The vetch furnishes a nice nest for overwintering beneficials such as minute pirate bugs, while canola and sorghum are home to lady beetles. The canola serves as a host through late spring, and sorghum houses beneficials through early summer.

“Grain sorghum bridges the gap left when the canola is destroyed,” says Slosser. “It helps maintain beneficials well into July when cotton blooms.”

Slosser says intercropping looks most promising for controlling cotton aphids. “For the 2000 crop, we planted cotton adjacent to our relay crops, and cotton isolated from our relay crops,” he says. “We also planted cotton into spring-planted wheat terminated with Roundup herbicide, as a third test.”

Early on, fewer aphids were in cotton planted next to relay crops than in cotton grown without relay crops. But their numbers increased about two weeks after aphid populations peaked in isolated cotton.

“On the other hand, whitefly numbers in cotton planted next to relay crops remained lower than in isolated cotton,” says Slosser.

He says more thrips but fewer fleahoppers were found in cotton planted adjacent to relay crops. The cotton's proximity to relay crops made little difference in bollworm numbers.

“This suggests relay intercropping can help suppress aphids to some degree,” says Slosser. “We also noticed more ground beetles and taller plants with more blooms per foot of row in cotton planted into killed wheat.”

Irrigated cotton planted into the killed wheat with adjacent relay crops produced about 1,200 lbs of lint per acre. That compared to a yield of 622 lbs from conventional cotton with adjacent relay crops and only 385 lbs for conventional cotton with no relay crops.

“We see major benefits of the relay crops, including better protection from wind erosion,” says Slosser. He adds that many beneficials in relay systems remained intact after cotton was sprayed for boll weevil eradication.

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