Southwest Producers Strike Back Against Resistant Pigweed

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Although it’s difficult to pin down the exact time frame that glyphosate resistant Palmer amaranth was discovered in West Texas, experts say there’s no denying that 2012 was the year in which the troublesome weed pest arrived in a major way.

Some weed scientists in the region claim to have had strong suspicions that certain plants had developed resistance to Roundup and other glyphosate applications as early as the 2010 growing season. The notoriously high winds of the High Plains can sometimes make it difficult for Extension researchers to know if a particular plant in a field is truly resistant to glyphosate, or if it has simply been missed by an application.

Nevertheless, official documentation came during the 2011 growing season. By the time the 2012 season rolled around, despite years of droughty conditions, glyphosate resistant pigweed – or careless weed as it’s called in the Southwest – had covered much of the High Plains.

“It seems like it’s just been expanding and expanding,” says Dr. Peter Dotray, professor and Extension weed specialist for Texas Tech University and Texas A&M AgriLife Research and Extension Service. “I’ve heard various people with different types of speculation as far as how much resistance we have here. A few folks think we may have it in as many as 40 percent of our fields.”

That percentage may not seem like a lot compared to the level of infestation seen in the Mid-South and Southeast. But Dotray operates in a 20-county region in West Texas that is home to roughly 3.2 million acres of cotton. If 40 percent of the fields in that large of a region have some degree of glyphosate resistance, it’s safe to say that West Texas is fully engaged in the battle against glyphosate resistant Palmer amaranth.

Dotray believes the level of resistance his region has seen has truly grabbed the attention of the segment of growers who may not have been as concerned with glyphosate resistance in recent years.

“I think some folks are paying more attention now than they had a year or two or three ago,” says Dotray. “That’s because the people who are talking about resistance now are their neighbors and people who live close by. So now the message is, ‘We know it’s here, let’s start implementing some of these strategies to prevent, or delay or at least keep levels to a very low level.’”

Implementing a Plan
According to Dotray, fighting glyphosate resistance on the High Plains is no different than fighting it in the rest of the Cotton Belt. The key in all regions is diversifying herbicide and weed management practices.

Some weed scientists theorize that the reason glyphosate resistance was delayed in appearing in the Southwest was because many growers in the region maintained effective uses of yellow herbicides. While that may have been the case, Dotray believes some growers on the High Plains had gotten away from that practice in recent years, and had begun over-relying on glyphosate products. That’s no longer the case, he says.

“I think there was also a good bit of folks going back to effectively using things like Treflan and Prowl and incorporating them prior to planting,” Dotray says, praising farmers who have taken a pre-emptive approach to diversifying their weed management programs. “I think a number of folks used different herbicides at planting. More intensive use of different herbicides up front is a good thing. I think folks are thinking about resistance this year, and making sure these weeds don’t escape applications.”

Although Dotray looks forward to testing more careless weed populations this season to determine if they are indeed resistant, the ideal scenario is one where the weeds never reach the first round of glyphosate applications. That’s why he stresses the need for early, pre-emptive action against the weeds.

As the season moves into July, and growers are dealing with escapes, Dotray says there are a variety of options for crop protection.

“I think it’s important for people to know that if they’ve got places in the field that have weeds that have withstood that glyphosate application, those weeds need to be removed,” says Dotray. “Whether it be physically removing them or getting out there and spot spraying some other kind of chemistry – something other than glyphosate needs to be used. We have to make sure those plants don’t continue to grow and set seed, and that small infestations don’t grow into bigger infestations that take over an entire field.”

Dotray says many growers in his area are beginning to re-evaluate the LibertyLink system to see if they can make it work to their advantage with more cases of glyphosate resistance cropping up in the area. He has high praise for stacked-trait herbicide technology as well.

“With cotton that’s tolerant to both Ignite and Roundup, it gives them a chance to use two very different post-emergent products in-season,” says Dotray. “I think more people are utilizing that strategy where they can spray the Ignite early, spray the Roundup a little later, and hopefully do a better job rather than just relying on either of one of those chemistries alone.”

Barnes is the senior editor /online editor for Cotton Grower, joining the staff in May 2008. In addition to writing for the magazine, he also oversees cotton247.com. Beck is also responsible for production of Cotton Grower eNews.
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One comment on “Southwest Producers Strike Back Against Resistant Pigweed

  1. Randy Rhodes

    I farm in Gates Co. North Carolina. I have a bad problem with Roundup resistant–Ragweed!! The Scout says that it is over a 3 county area or more. I had it in "Wheat soybeans" & I sprayed with 1/2 gal. of Flexstar GT & it knocked them out. Had cotton there last year & "The Ragweed" also. Want to plant wheat again this year too behind these Ragweed infested cotton. Don`t know to plant wheat, or let it lay out for full season beans next year & treat the land early before they start growing. (got marestail TOO)