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UT cotton field day shows off latest work

NEW INSECTICIDE TRAITS soon on the market offer potential benefits to growers says Scott Stewart Tennessee Extension entomologist
<p> NEW INSECTICIDE TRAITS soon on the market offer potential benefits to growers, says Scott Stewart, Tennessee Extension entomologist.</p>

Cotton acreage may be trending down in west Tennessee, but research on the crop continues at the University of Tennessee’s West Tennessee Research and Education Center at Jackson.

At a recent field day, researchers talked about their work on several projects aimed at keeping cotton competitive with corn, soybeans and wheat. New irrigation technology, for one thing, offers promise in this region, where many new center pivot irrigation rigs were installed the past couple of years.

“We’re taking a close look at subsurface drip irrigation. While that is not widely seen in Tennessee, farther west there’s more going in all the time because of limited water supply,” says Chris Main, Tennessee Extension cotton specialist. The experiment station now partners on subsurface drip irrigation work with John Deere Water and Tennessee Tractor’s irrigation division, which provides additional funding.

Farmers in this area likely will use subsurface drip differently than those in Texas, Main says. “Here, drip will be for fields where we can’t get pivots in, for whatever reason. On smaller acreage, drip works well,” he says.

This is the university’s first year of work with subsurface drip. Tape was installed in February; plots got water in early June.

“Tape was installed on every other row on 38-inch cotton. We try to feed two rows off one tape. This is thick-walled tape that should have good durability. It is 12 inches deep. We’re trying to figure out if one tape every 76 inches or 38 inches is better,” Main says.

“We see that it can be a good solution to get water on odd-shaped fields where a pivot won’t work. We can supply nutrients through the tape right at the root system. Right now, we think when farmers get started with subsurface drip, they shouldn’t be too concerned with putting nutrients through it until they figure out what they’re doing. Just doing the water is the first step. Start small. Start with 20 or 30 acres.”

In another irrigation test, moisture sensors buried at depths ranging from 4 to 40 inches below the soil surface indicate when conditions are right for watering the crop.

“I can look at what the water is doing at different places in the soil profile and see how that plant is using water. Using it, we can really see the rainfall events move in and what they did. It’s a neat tool,” Main says.

Irrigated cotton makes better use of sunlight, as well, UT’s scientists think. Their tests indicate that, with irrigation, the crop harvests 80 percent of the sunlight falling on the field. Dryland cotton, on the other hand, catches just 60 percent of the sunlight.

To truly understand how irrigation helps produce a good-yielding crop, it helps to know just how little water is required to turn one out, as well.

“We’re trying to get optimum yields without optimum water. We want to get less vegetative growth and more lint, and make better use of rainfall if there is some capacity to grab it and hold it,” says Brian Leib, UT biosystems engineer.

Cotton growing on good soil requires less water. Six of seven years, cotton in good soil actually lost yield with early irrigation. In sandy soil, though, cotton needs early irrigation to maximize yield.

“The biggest yield bumps come from applying irrigation to cotton on sandy soils,” Leib says.

This year, Leib and his co-workers began looking at how varying rates of irrigation affect crop yield.

“We’re trying to find that one irrigation decision that might optimize yield over varying soil types. On sandy soil, you probably can get close to optimum yield with one-half inch of water a week starting early, at square, and going right through cracked boll. This will probably utilize the least water and make the water most efficient,” Leib says.

“Is this going to push us to precision variable rate irrigation? That’s something to consider.”

Insect problems

Scott Stewart, Tennessee Extension entomologist, says cotton farmers in the area dealt with new insecticide resistance problems this year, leading to questions about how to control aphids in 2013. Aphid numbers in west Tennessee usually are fairly low. This year, however, aphids boomed in some fields.

“We saw failure of the neonicotinoid insecticides in cotton. They provided essentially no aphid control. Using the neonicicotinoids early has resulted in resistant aphids. I think we’re going to be seeing more aphids now,” Stewart says.

“So we can go out there and apply those products and get 20 percent control or even negative control. It’s a reason to use the other products available.”

Additional new technology traits could help cotton farmers ward off insects, Stewart says. TwinLink, a dual-Bt cotton set for release in 2013 in a package with LibertyLink tolerance, shows promise, comparing favorably to Bollgard II varieties. Other traits, Bollgard III, WideStrike III, and TwinLink Advanced, with three Bt proteins, should be marketed within a few years.

“It’s conceivable that this could put us out of the worm spraying business, if the price is right,” Stewart says. “To be honest, I’m not disappointed with where we are right now with worm control. There are some good new insecticides out there. Hopefully, if the price gets right, we can adopt those worm-specific products.”

Palmer pigweed

With glyphosate-resistant Palmer pigweed foremost in most west Tennessee farmers’ minds, UT researchers continued to look at ways to best control it. Early control with residual herbicides like Cotoran, Caparol and Reflex worked best, even in the LibertyLink program, says Kelly Barnett, a UT doctoral student working at Jackson.

“A lot of 6-inch pigweed didn’t go down easy, even with one shot of gramoxone,” Barnett says.

“Our only post-emergence option is Liberty, not Roundup. I want to stress that. And it’s no good to apply Liberty to pigweed that’s too big or with the wrong nozzle or in the wrong weather conditions. The pigweed has to be 4 inches tall or less. When it’s bigger, you may get control at times, but it will be inconsistent.”

Best Palmer pigweed control comes when applying Liberty in at least 15 gallons of water per acre through flat fan nozzles, Barnett says. Application timing is critical, as well.

“Go at least two hours after sunrise. Applications near sunrise give 40 percent to 50 percent control. We’ve seen even better control by waiting until four hours after sunrise. Applications at 10 a.m. give greater than 90 percent control. Time of day will influence how Liberty is working,” she says.

Liberty is “finicky,” Barnett says. “The very narrow window to apply Liberty shows how finicky this herbicide is.”

Cover crops

Matthew Wiggins, another UT doctoral student, spent the summer looking at how cover crops might be used to curb Palmer pigweed problems.

“We’re proving that not only will cover crops prevent erosion, but they can also perhaps shade out pigweed early in the season,” he says.

He’s investigating winter wheat, cereal rye, crimson clover, hairy vetch and Australians winter peas. “We’re also mixing them in the drill to see if we get any benefits from a combination of these,” he says.

It’s best to plant cover crops early, Wiggins thinks, so they can get good growth before winter dormancy.

Those cover crops could change how west Tennessee looks, if nothing else.

“It’s going to look like Ireland around here this winter,” says Larry Steckel, Tennessee Extension weed specialist. “I’m getting a lot of calls on cover crops. I think it can help us with pigweed. It saved a burndown application and took out marestail and helped us on the front end with pigweed. The complete answer to pigweed cannot be poured out of a jug. We have to get some cultural things back into play.”

Steckel says USDA’s Natural Resources Conservation Service will share costs of cover crop seed.

West Tennessee farmers haven’t conquered resistant Palmer pigweed yet but many are managing it better. “We’re in a lot better shape now than we were last year,” Steckel says.

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