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A look at Roundup Ready Flex cotton

MONROE, La. -- Still a year away from commercial release Monsanto’s Roundup Ready Flex cotton is already garnering much interest.

“We’ve been conducting research on Flex in hopes of answering as many questions as possible about this technology prior to its commercial release,” said Donnie Miller, associate professor with the LSU AgCenter. “Anyone who’s grown Roundup Ready soybeans has a pretty good idea of what’s coming with Roundup Ready Flex cotton.”

The predecessor’s impact

Since its release, Flex’s predecessor, Roundup Ready, has revolutionized the U.S. row-crop landscape.

“Last year, approximately 489,000 cotton acres were planted in Louisiana,” said Miller, who spoke at the Louisiana Cotton Forum in Monroe. “It’ll surprise no one that the vast majority of those acres were planted in transgenic varieties to help with insect and weed control. A large number of those varieties have a Roundup Ready component.”

In 1996, when Miller first began his work with the AgCenter, “I remember being asked what I thought the impact of Roundup Ready technology would be. At that time, it was already in soybeans.”

The impact, he said, has proven massive. “We thought it might replace some of the early post-emergence directed applications. That, obviously, would affect Cotoran and MSMA applications and possibly cut back on some pre-emerge applications.

“It’s instructive to see use of several herbicides (in Louisiana) since 1998, a couple of years after the release of Roundup Ready cotton. Back then, according to the USDA National Ag Statistics Service (NASS), we were using about 79,000 pounds of active ingredient glyphosate. Pyrithiobac (Staple) was at 10,000 pounds. Fluometuron was around 340,000 pounds. MSMA was at 470,000 pounds, and diuron was about 110,000 pounds.”

Fast forward five years to 2003 — the last year data is available — and check the same chemicals. Calculating percent change between the two years, Louisiana glyphosate use increased 715 percent. Staple use decreased 80 percent. Fluometuron use dipped 85 percent, and MSMA decreased 65 percent.

The one herbicide other than glyphosate that saw an increase was diuron — up about 134 percent. The elimination of Bladex played into that, said Miller.

“Also, those working a Roundup Ready system often found a need for residuals.”

For the entire cotton producing area of the United States from 1997 to 2003, trends are very much the same. Glyphosate use increased 753 percent. Yellow herbicide use decreased 25 percent. Diuron use increased 101 percent. Staple experienced a 26 percent decrease. Prometryn decreased 28 percent. MSMA/DSMA decreased 74 percent. Norflurazon and bromoxynil both decreased 97 percent.

“Roundup Ready technology has had a tremendous impact on the use of other materials.”


Several key benefits made the shift to Roundup Ready so precipitous, said Miller.

“First, it can reduce the number of herbicide applications and tillage operations. That can decrease labor costs. The second benefit is the easy application trigger. When the first flush of weeds comes up at the 1-inch to 3-inch stage, just make the glyphosate application. It has a broad spectrum of control. Gone are the days when we had to tank-mix, or apply chemicals separately to kill grass and broadleafs — you can get both with a single application.”

Currently, there are several approaches to Roundup Ready cotton.

“A few people go with just glyphosate. Others treat the cotton as Roundup Ready until the fourth-leaf restriction hits, and then they treat it like conventional cotton with no glyphosate going out. They fear possibly delaying maturity or affecting yield.

“Still others combine the two: spraying glyphosate to a certain point and thereafter combining glyphosate with more conventional chemistries.”


Along with the benefits of Roundup Ready, Miller cites problems.

“There have been issues with proper application timing. Obviously, to get your money’s worth, you want two applications over-the-top. But it’s often very hard to get those applications in before the four-leaf stage.”

One of the “bigger problems” is fewer conventional varieties developed and released.

“Also, from weed control standpoint, there is much less product development and modes of action coming. Companies aren’t putting in the time, effort and, especially, the money to find new compounds. That has been a real drawback with Roundup technology.”

Roundup Ready Flex

Spraying guidelines for Roundup Ready Flex will be far more tolerant than the current four-leaf spraying restriction on its older brother. The new system essentially allows glyphosate over-the-top spraying throughout the growing season. There may be much less reliance on specialized application equipment.

“Post-directed rigs already are parked. I think we may see more hooded sprayers and lay-by rigs. This will be more like weed control in soybeans — bigger, faster equipment across the field.”

Having recently spoken with Monsanto’s product/development manager for Flex cotton, Miller said the product label is still in review by EPA and is not yet finalized.

“The main thing to know: you’ll have plenty of glyphosate available to apply for weed control.”

The temptation

With Roundup Ready Flex, growers can go with higher rates and make over-the-top applications later in the season. The temptation will be to delay the initial application. Studies show the folly of this approach, said Miller.

Miller and colleagues have been studying Roundup Ready Flex for several years. “We wanted to answer as many questions as we could with a limited amount of seed. It isn’t the same cotton that will be released to the market, but it gave us an idea of its tolerance.

“We used rates as high as 1.5 pounds acid equivalent per acre. The one blip we saw from an injury standpoint was with the higher rates — 1.5 pounds, 1.25 pounds. The year we did this test, we got a lot of rain during a cool, early growing season. When we made the higher rate applications, we saw some burning and crinkling of leaves. That was attributed to the high surfactant loads in the formulation at those higher rates. Leaves that came out after the spraying were fine, and the cotton growth didn’t check up one bit.”

The research cotton ran into problems from weed competition when the initial glyphosate application was delayed.

“When we waited until five-leaf to eight-leaf cotton, we had to put out higher rates because the weeds were much larger. We still had excellent control but, at the time, we couldn’t see the yields we’d sacrificed. With early applications, we got 2,150 to 2,346 pounds of seed cotton. Where we delayed applications to five-leaf cotton, the crop produced 1,647 pounds to 1,867 pounds of seed cotton.”

Of course, weed competition isn’t something researchers are just now looking at. Back in the 1970s, studies found that cotton yields would be maximized if growers kept a field weed-free for eight weeks after emergence.

“If you went weed-free longer than that, it had no effect on yield.”

Adding to the tank

Miller also wanted to see how integrating management systems in Roundup Ready Flex cotton would work.

“We decided every time we made a Roundup WeatherMax application, we’d add something else to the tank — insecticides or Pix. We wanted to see if mixing them antagonized weed control or adversely affected the crop in any way. We saw no effect from any co-applications. That was very impressive.”

Miller has a graduate student working near Alexandria, La., researching weed control programs in Flex cotton.

“In one study, he looked at the effects of pre-emerge (fluometuron) versus no pre-emerge in combination with a variety of post-emerge programs: 22 ounces of Roundup WeatherMax over-the-top at three-leaf, seven-leaf, or 14-leaf.”

With Roundup Ready Flex, you have an opportunity to take advantage of a residual mixed with glyphosate. In another study, various combinations of glyphosate and residual materials were used at several timings applied over-the-top — a two-shot program.

“You need something early — whether pre-emerge or not — to take care of the early flushes. And in years like the last, when rainfall occurred early and then dried up, we needed something late to clean up.”

No difference was found between post-emergence or post-directed applications. Even when treatments went out on 14-leaf cotton, “we still got enough coverage into the canopy so a specialized lay-by rig wasn’t needed.


Another Roundup Ready Flex positive: the opportunity to make co-applications.

“We can possibly co-apply insecticides, micronutrients and PGRs with glyphosate to limit the number of total in-season applications. This ability is great, but we don’t want to sacrifice weed control. So we’re checking to make sure the weed control isn’t hampered by co-applications.”

Five common weeds in cotton were studied: johnsongrass, hemp sesbania, barnyardgrass, pitted morningglory and sicklepod. For each weed, mixtures of glyphosate (Roundup Ready WeatherMax) with many insecticides, micronutrient solutions and a PGR were applied at two growth stages: three-to four-leaf or seven- to eight-leaf.

“With all weeds there was no problem with co-applications — we got great control and no negative effects when compared to glyphosate applied alone, regardless of growth stage at application,” said Miller.


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