As glyphosate-resistant weeds continue to march across the Mid-South, many farmers are being forced to pull old weed control technology out of the grass patch.
For some, it’s almost like weed control has been transported back to the 1980s, what with all the cold steel, post-directed rigs, hooded sprayers and residual herbicides becoming more prominent in the arsenal.
And weed control costs are rising, too, as well as a critical importance on application timing, both of which came into focus during the weird growing season of 2009, when wet weather prevented so many timely applications.
A resistant pigweed problem got so bad for Gunnison, Miss., producer Kenneth Hood this season that he had to plow under some soybean acres infested with it “after I threw everything I could at them and couldn’t control them.
“It’s unbelievable how thick they have become since my last disking. If that is any indication of what I’ve got to fight next year, I hate to think.”
Cold steel is not the only old technology pulled out of the closet the last two years, Hood says. “We’ve hand-weeded and spot-sprayed weeds by hand. We never stopped our post-directed applications. We just went out and tried to control those spots in the field where resistant weeds escaped our traditional applications.”
Hood estimates that the additional trips and labor has increased his cost of production by about $30 an acre, “and we’ve hurt yields and quality as well. Weeds will choke up cotton pickers and combines, and hurt the quality of your crops. Resistance is a broader spectrum problem than we think about.”
Weeds in the Mid-South with documented glyphosate resistance include johnsongrass, horseweed, common ragweed, Palmer amaranth (pigweed) and Italian ryegrass.
Cleveland, Miss., rice and soybean producer Nott Wheeler says he is also spending more money on weed control because of resistance. “It’s okay as long as soybeans are $10 to $11 a bushel. If the market turns, and I’m confident that someday it will, we will have to weigh the cost of those applications more heavily. At these price levels, we can afford to keep soybeans clean.”
Wheeler rotates his rice and soybeans, which is a good way to use different chemistries on resistant weeds. “In soybeans, you get a two-year shot at them, a chance to clean them up.”
In rice, resistant pigweed has been an early-season problem for Wheeler. “Once we water up, they pretty much go away. But we’ve had some infestations that were bad enough where we’ve had to treat.”
Palmer amaranth (pigweed) has always been a prolific breeder and seed producer and grows quickly, but glyphosate resistance has taken the weed to another level for Mid-South farmers.
“It doesn’t take much of letting pigweed go before it will take over,” Wheeler said. “In our experience, we didn’t see it as a big problem because it was coming late in the season, and it wasn’t affecting our yield. Then it got to be a problem coming up in the spring and we couldn’t do anything with it.”
Wheeler has had success using residual products in soybeans to get them cleaned up. “We have put out Valor and Prefix, and that’s helped a lot. We’ve used FlexStar to get better control early on.”
Hood first noticed pigweed escapes about four years ago and thought careless applications were to blame. “You’d have five dead plants and one live plant sticking up. It took us a while to understand that we had resistance. I’ve had to apologize to my farm equipment operators for getting on to them when resistance was the problem, not misapplication.”
Timing and knowledge of a resistance problem are two keys to controlling resistant weeds. But in 2009 wet weather wreaked havoc with timing.
“I was fully aware of resistance problems prior to the 2009 season,” Hood said. “We hit it with everything we could. The problem was the May rains. We planted the crop, got it up, and even though we thought we had done a good job with post-directed sprays, we couldn’t do them in a timely manner. The weeds had gotten too large.
“Pigweeds turned completely brown, but in four days time, they started greening up and took off again. That’s what you run into when your timing is off. Timing is the most important factor for controlling resistance. If you hit them when they’re small, and you hit them hard enough, you can control them.”
In cotton, Hood plans to increase his use of preplant and pre-emergence herbicides, including Prowl and Dual. “It had been 10 years since I’ve used any kind of yellow herbicide in cotton, but the little bit I put out last year worked perfectly.
“But it needs to be incorporated for pigweeds because they can come from so deep in the soil. There are some other products out there that you don’t have to incorporate, but they take some rainfall.”
The products will have to hold for a while, noted Hood. “These resistant weeds will start coming up preplant and will keep coming up through August. That’s what makes the problem so severe and runs up the cost of production so much.”
A late season residual in cotton may also be necessary in cotton, Hood says. “A lot of farmers had gotten away from a layby in cotton because Roundup Flex cotton allowed you to use Roundup all season long. But we’re going to have to go back to a residual now, and maybe two.
“We may want to put a layby out in July, early season, and we may have to put another layby out in August.”
Both Wheeler and Hood say glyphosate remains a very viable tool in weed control. “It still does a good job,” Wheeler said. “We have a few more arrows in the quiver. It doesn’t matter whether it’s glyphosate or propanil, if you use it enough, something is going to become resistant.”
Hood says glyphosate “will still be in our arsenal, but we will not be relying on it as extensively as we have in the past because of the resistance issue.”
Current technologies like LibertyLink cotton and soybeans can address the weed resistance issue, but again, timing is a critical issue, noted Hood. “You have to hit the weeds when they’re small.”
Upcoming technologies such as dicamba-resistant varieties can also help with glyphosate-resistant weeds and grasses, according to Hood. “But I can’t wait three years.”
In the meantime, Hood says, “If farmers are going to be forced to apply residuals and change tillage practices, do more spot spraying and post-directed sprays or have to change crop scenarios to change chemistries for better control, then I can’t afford to pay for a technology fee. Economics will force me to go to a germplasm or seed variety out there where I don’t have to pay for that. Hopefully, those will be available to us.”
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