Benefits, disadvantages seen in RR

Rarely, if ever, has a new technology been adopted on a scale approaching that of Roundup Ready cotton. In Georgia alone, about 82 percent of the cotton acreage in 2001 was planted to Roundup Ready varieties.

“The technology was released in 1997, and by 1999, 50 percent of our crop was being planted in Roundup Ready varieties,” says Stanley Culpepper, University of Georgia Extension weed scientist. “In 2000, approximately 72 percent of our state's growers were planting Roundup Ready varieties, and we expect another slight increase this year.”

Of the 82 percent planted in 2001, 40.8 percent was Roundup Ready alone and 41.5 percent was stacked gene varieties. “I don't know of any other technology that has been adopted at such a rate,” says Culpepper.

There are many benefits to using Roundup Ready technology, he says. “Obviously, we depend less on soil-applied herbicides when we use Roundup Ready. We're probably also reducing our herbicide costs. I know we're not using as much Cotoran, and it probably was applied on every acre of cotton in Georgia prior to Roundup Ready. In most cases, we're not eliminating soil-applied herbicides, but we are reducing their use,” he says.

Roundup Ready technology also helps farmers save labor and power, he adds.

“Roundup Ready technology allows us to get away from directed applications. Instead of running 3 or 4 miles per hour and getting injury on cotton, we're running 8 to 10 miles per hour and carrying 5 to 10 gallons of water. It's much more efficient,” says Culpepper.

Roundup Ready also has led to a more widespread adoption of conservation-tillage, he says. The technology, he adds, offers many more options for controlling weeds, thereby easing the transition into conservation-tillage systems.

The weed control systems used with Roundup Ready cotton are equal to those in conventional programs, he says. “Many growers claim to get better control because they're allowed to make more untimely applications. With Roundup Ready technology, you can get away being two to three days late with herbicide applications.

“We've proven consistently that if you're timely, and if Mother Nature or equipment doesn't keep you out of the fields, the conventional program is every bit as good as the Roundup Ready system, except for those few farmers growing ultra-narrow-row cotton. There's no doubt that the ultra-narrow-row growers couldn't do what they've been doing without Roundup Ready.”

The technology is easy, and it kills big weeds. This pretty much sums up the advantages of Roundup Ready as seen by most growers, says Culpepper.

There are, he says, a few negative issues associated with the use of Roundup Ready cotton varieties.

“The technology is wonderful. But it's questionable whether or not we're using the technology as we should in many cases. Some of the negative issues include weed shifts, untimely applications, yields and net returns, fiber quality and resistance.”

Weed shifts, he explains, are a change in the distribution of a weed species in a given field. A growers most likely will see an increase of one weed species and a decrease in another species based on the adoption of a certain practice, such as the planting of Roundup Ready cotton.

“Before Roundup Ready was introduced, sicklepod was a major issue for cotton producers. As more growers have adopted this technology, sicklepod no longer is an issue. Four or five years ago — before the introduction of Roundup Ready — growers were aware of tropical spiderwort, but they did not consider it to be a major problem.

“As we have adjusted to Roundup Ready technology, spiderwort has continued to increase and become a problem weed for some Georgia growers.”

As more growers have adopted Roundup Ready technology, there have been problems with weeds in addition to spiderwort, including Asiatic dayflower, morningglory, hemp sesbania and Florida pusley, notes Culpepper.

“There are negatives to using this technology, and that's because we're relying so much on the technology that we're pushing these weed shifts. Tropical spiderwort probably is the most troublesome weed in Georgia now — not the most common, but the most troublesome.

“Tropical spiderwort is very difficult to handle because we're better than 82 percent planted in Roundup Ready, and this weed is tolerant to glyphosate. With 8 pints of glyphosate, we're still getting only 90 percent control of this weed. We're also concerned about marsh dayflower. Glyphosate gives us only 50 percent kill on this weed. Fortunately, marsh dayflower is low-growing and less competitive than tropical spiderwort.”

A common problem with Roundup Ready technology is untimely applications of glyphosate by growers, says Culpepper. “Some growers are applying glyphosate too late, some are going over-the-top after the fourth true-leaf stage, and some are sloppy-directing glyphosate.”

The first four or five weeks after emergence is very important, he says, and late applications of glyphosate can result in reduced cotton yields.

“In heavily infested fields, three postemergence applications may be necessary in the absence of residual herbicides while only two may be needed when following soil-applied herbicides. Additionally, in heavily infested fields, postemergence applications often need to be initiated on one-leaf cotton when not following soil-applied herbicides. Postemergence applications could be delayed to three- or four-leaf cotton when following soil-applied herbicides.”

It's very common, says Culpepper, for Georgia growers to apply glyphosate over-the-top after the fourth true-leaf stage. “Probably 50 to 70 percent of our cotton in 2001 was treated with glyphosate after the fourth true leaf. Again, we can reduce yield by doing this. Research has shown that if we apply glyphosate at the five- to nine-leaf stages, we can reduce yield by 20 to 22 percent. We impact that plant through loss of fruit, delayed maturity and, ultimately, yield loss.”

Georgia research in 2000 and 2001 showed significantly higher yields when precision-directing glyphosate as compared to sloppy-directing the herbicide, he says.

“Additionally, laboratory research has noted that cotton stems readily absorb glyphosate, and that the glyphosate then is translocated to the fruit.”

Turning to yields, Culpepper says Roundup Ready alone varieties haven't performed very well in state and regional trials. “Stacked-gene varieties have looked very good. But Roundup Ready alone consistently ranks near the bottom in yields. You have to look at the data and select the varieties that look best in your area. As of now, Roundup Ready alone isn't looking positive anywhere.”

In tests comparing fiber quality, there was no significant difference in Roundup Ready varieties when glyphosate was applied in a timely manner, he says. Untimely and non-precise applications, however, could be causing quality problems, he adds.

Resistance development is another concern with the use of Roundup Ready technology, says Culpepper. “Resistance is when a weed - once controlled by a herbicide - no longer is affected by the herbicide. Already, we have confirmed pigweed resistance to ALS herbicides in eastern Georgia, pigweed resistance to DNA herbicides and possibly goosegrass resistance to paraquat.

“And we now have three confirmed cases of resistance to glyphosate. When we plant 82 percent of our acreage in Roundup Ready, and we spray glyphosate two to three times, we're selecting very hard for resistance. Enhanced Roundup Ready is four to five years away. But by the time it's introduced, it might not be of much use to many growers because of resistance problems.

“We must manage our resistance, whether we use other herbicides, rotate or use other practices. We must quit putting so much stress on glyphosate alone. We have to help preserve this technology.”

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