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Quirk weed control trait confirmed

Steve Wright, University of California Cooperative Extension farm advisor in Tulare County, has confirmed that an Acala cotton variety resistant to insects and glyphosate is also resistant to glufosinate herbicide at high rates.

If growers plant Phytogen 755 WRF, they only have to pay for two traits. The third is free, a coincidence of the biotechnology process to develop the insect resistant trait (WideStrike).

University of Georgia and University of Tennessee weed scientists have reported on this quirk of science, but Wright’s work for the past two seasons at the Westside Research and Extension Center at Five Points, Calif., confirmed that the 755 Acala has the same attribute as its Southern upland cousins.

Wright tested four different timings and three rates of the herbicide commonly known as Ignite from Bayer CropScience. The glufosinate-ammonium herbicide has been renamed Rely 280 in the West. It may be Ignite elsewhere in the Cotton Belt.

The herbicide applied at rates as high as 21 ounces per acre active ingredient (86 product ounces) over the top of the cotton caused injury at the two true-leaf stage, but the cotton grew out of it, generally in 21 days, according to Wright. It was applied on May 8, May 15, June 2 and July 16.

“Growers are used to a little injury with some products applied over the top, at least in cotton and grain crops,” and that is not expected to be a concern to producers, Wright said.

Wright compared the three Rely 280 rates against treatments of Staple and Agridex and Roundup Weathermax, all over the top treatments. Overall yields were low in the trial due to heavy lygus pressure. However, Wright said there were no yield differences between treatments.

Fortunately, growers do not have to pay for the trait either to Dow AgroSciences, which markets the cotton, or to Bayer CropScience, which markets Rely 280.

Dow charges San Joaquin Valley producers only $5 per acre for the WideStrike trait, much less than elsewhere across the Cotton Belt. This is because worm pressure is generally lighter in the West than other areas.

Unfortunately, however, neither company stands behind the use of the herbicide over the top of cotton, even though, the herbicide is registered for use on the crop.

“Right now my official statement is that we do not want to see the use of it over the top on Phytogen WideStrike cotton and Bayer does not want the herbicide applied over the top,” said Duane Canfield, market specialist, cotton traits and seed, for Dow AgroSciences.

The fluke of science may be welcome by many growers who are battling resistant weeds like palmer amaranth in the Mid-South and those struggling with broadleaf control and issues of glyphosate resistance in the West. One emerging glyphosate-resistant weed issue in the West is horseweed and researchers elsewhere have reported good control of resistant horseweed with glufosinate.

Wright suspects the reason companies are not endorsing the use of Rely over the top of Phytogen 755 WRF is because it does not meet a critical standard for safety at rates as high as four times or more the label rate.

Canfield added Dow is coming out with a second herbicide trait offering resistance for cotton to 2,4-D and other herbicides along with the existing Roundup Flex gene. Monsanto is combining existing glyphosate-resistance with dicamba resistance in cotton for release within the next few years. Bayer will be adding a gene to its Liberty Link cotton to make it resistant to glyphosate as well as Ignite/Rely 280.

Canfield believes this new generation of double herbicide resistant cottons will offer growers better tools for controlling resistant weeds.

Tulare County farmer Mark Watte used Ignite over the top of 755 WRF last season to control broadleaf weeds that glyphosate (Roundup) may be weak on.

“It works well on nightshade and morningglory,” said Watte. Ignite/Rely 280 also controls Palmer amaranth, woolly cupgrass, velvetleaf, cocklebur, foxtails, ragweeds and waterhemp, along with ALS-resistant and glyphosate-resistant weeds, according to Bayer.

Dow says the glufosinate-resistant gene is the selectable marker in WideStrike cotton varieties and why the herbicide resistance trait is in all WideStrike varieties.

However, the tolerance to glufosinate ammonium herbicides provided by the gene in WideStrike is not equivalent to the glufosinate ammonium herbicide tolerance of LibertyLink cotton, according to Dow.

Wright said he conducted his research based on findings from University of Georgia Extension weed specialist Stanley Culpepper who first discovered the transgenic coincidence.

“There have been some disappointments with the use of Roundup for nightshade control. From a grower’s perspective, having an alternative like Rely early over the top is attractive,” said Wright.

Wright said the WideStrike/glufosinate quirk is not widely known and “we are not promoting it, since it is something that is technically not on the label. We provide the research results as information only.”

Wright plans one more year of trials, “but after that I am moving on to other projects. It is up to the companies to decide if it worth it to change the labels. I know a lot of growers would appreciate the availability of this technology,” said Wright.

That could be really appreciated this year as above average rainfall has spawned a crop of weeds not seen in seven years.

”With all this rain we have been having, it is hard to recognize when the winter annual weeds quit and the summer weeds began. We are seeing a lot more nightshade and morningglory as well as weeds in the mustard class,” Wright noted.

Regardless of the class of weeds there, Wright said it is imperative growers hit them early to gain the upper hand.


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