The unfortunate combination of low cotton prices, herbicide-resistant and tough-to-control weeds, and the vagaries of in-season weather puts an exclamation point on farmers’ need to establish a weed control system that will improve the odds of producing an economical crop.
“It’s not too early to begin thinking about what you will do in-season,” says Shane Osborne, Oklahoma State University associate Extension specialist at Altus. At the Carnegie Cooperative Cotton Conference, an annual event held at Carnegie, Okla., he offered a detailed system for managing weeds through a tough economic season.
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“Cotton farmers have a market crunch on one side and an input crunch on the other,” Osborne says. They are also dealing with a different weed spectrum than they did just three years ago, when their main threats were horseweed and morningglory, according to 56 percent of farmers surveyed for 2016. Morningglory was rated the most difficult to control by 19 percent of those surveyed, and pigweed by only 12.5 percent.
That’s in contrast to the 2015 survey, in which 86 percent of respondents picked pigweed as the hardest to control, with horseweed at only 14 percent. Both of those have glyphosate resistance.
Control costs have soared as well, Osborne says, going from less than $40 per acre in 2013 to over $100 per acre in extreme cases. “That’s just not feasible,” he says, adding that new chemistry to match new seed technology released in 2014 offers hope for managing herbicide-resistant weed species — but it probably won’t be available for 2016.
Even with those new tools, farmers should take a calculated, season-long approach that includes a burndown treatment, preplant incorporated application, preemerge, early postemergence treatment, and possibly later over-the-top applications of the dicamba or 2,4-D products paired with XtendFlex (Monsanto) or Enlist (Dow AgroSciences) seed technology.
Hooded sprayers, cultivation, and hoe hands also may be necessary in some cases to clean up escapes, Osborne says. BASF also offers Engenia for use in XtendFlex cotton.
Although not labeled for use in 2016, “The key with the new auxin technology is that it will be best used as part of an overall system that continues the integration of residual chemistry,” Osborne says.
He also cautions farmers about overuse of the new technology, especially as regards potential resistance issues. “When Roundup Ready seed was released, we had essentially no weed species identified as resistant to glyphosate. Now, with the dicamba and 2,4-D traits, we already know of 32 weed species with resistance to that herbicide family.”
Dicamba or 2,4-D alone are not as effective as glyphosate alone used to be, he says. “This makes it imperative that growers spray weeds at the right time. Weed size at application will be important. Producers should remember that they get no help from Roundup within a tank mix when they are going after glyphosate-resistant pigweeds.”
SYSTEM IS ESSENTIAL
While 85 percent control in a cotton field was once considered acceptable, that’s no longer the case if producers are dealing with glyphosate resistance. That’s why a system — including burndown, preplant, preemerge, early post- and late season control strategies — is essential, Osborne says.
“It may be a good time to get familiar with Liberty — specifically, in-season use. Many growers are still not familiar with this herbicide. Targeting small weeds is important. So is volume. Fifteen gallons of water is recommended with Liberty. It does matter, especially in a salvage situation. Follow the label.” Most importantly, the grower needs to have a Liberty Link variety in order to apply Liberty in-season.
Paraquat is a useful burndown alternative to eliminate glyphosate-resistant pigweeds at planting. Preplant applications should be routine, Osborne says. “Yellow herbicides continue to be important, even after we get new chemistry. We have a lot of opportunity to see the value of yellow herbicides. Treflan and Prowl H2O are still very effective on Palmer amaranth and small-seeded annual grasses.
“Incorporation is essential with Treflan (either plowed in or through chemigation), and although Prowl H2O is better with mechanical incorporation, it is also very effective against glyphosate-resistant pigweed as a preemergence application.”
“An effective residual herbicide is crucial,” Osborne says. “Making sure to get good coverage with new products and a residual should allow producers to expect excellent control.”
Postemergence, over-the-top materials include Staple, Dual, and Warrant. “We have a few good products that can be tank-mixed and applied over-the-top in cotton,” Osborne says. Aim, Caparol, Cotoran, Karmex/Direx, Valor, Anthem Flex, and Zidua are available for use with hooded or shielded sprayers.
“Anthem Flex and Zidua only offer residual control, not burndown, but they make good tank mix partners with other burndown materials like Aim, Valor, or Liberty.
Osborne says 2015 “was a good Liberty year” — humid and damp. “But this is not always the case for our region. In hotter, dryer years, Liberty may be less consistent, so it is more important to follow the product label closely to get good performance.”
KNOW YOUR FIELDS
Field history also makes a difference in developing the most economical weed control system. “Know your farm,” Osborne says. “Know which weeds are in each field, and which product will control them. Otherwise, costs can ruin hopes of a profitable year.”
On dryland acres, he says, farmers should ask themselves if they battled resistant weeds last year. The next question should be, “Can I afford to change practices?” Know what you’re up against, he says. “If you saw pigweed last year, you’d better have a plan.”
Rotation is important, too, especially if cotton may be following last year’s wheat crop. “Think about the wheat herbicide history. Finesse, Ally, and Cimarron Plus have a 14 month plant-back restriction with cotton. However, if the soil pH is high, that restriction could be 34 months.
“Also, in no-till wheat, you may see some resistant pigweeds. Many producers who have continued to spray no-till wheat ground in the summer with glyphosate only have been seeing a buildup of resistant pigweeds. If those weeds went to seed last year, you can expect big problems this year.
“Dryland budgets are so tight we can’t afford to take an uneducated approach. Consider all practices and make sure each one is sound. The key is to scrutinize everything — don’t invest in anything that’s not proven. One thing for sure, your weed control budget could easily be doubled, so any savings garnered elsewhere will be valuable.”
Effective weed control starts early, Osborne says. “The beginning is the most critical with glyphosate-resistant weeds. If resistant weeds are up before planting, you can’t miss the opportunity to take them out, using another effective chemistry, such as paraquat. In these cases, don’t use Roundup as a burndown.”
A plan is essential, he says. “Plan on using specific herbicides where they offer the best option for control — paraquat versus Roundup at planting, for instance; Prowl H2O versus Warrant at planting or early postemergence. The key is to build in the most flexibility possible.”
Valor applied 14 to 30 days before planting “is a good fit for no-till, but we still want to apply a yellow herbicide at planting.” The early post application is critical with Roundup or Liberty, he says. “If you don’t know the field history, be prepared for the consequences. And be ready to deal with escapes with a hoe, cultivator, or an application of Liberty.”
This year, variety selection may be even more important than usual, Osborne says, and suggests that picking a variety that permits in-season use of Liberty will be a good option.
“To be profitable, producers will need a system with flexibility, and that should include Liberty Link, Xtend Flex, or Enlist. All of these offer tolerance to Liberty herbicide. Residuals are still the key, and focus on eliminating competition early in the season. Weed size at application is critical, as is paying close attention to the label.
“Randy Boman, OSU Extension state cotton leader, says dryland cotton farmers will need to look hard at weed control costs. Consider every option carefully to justify the expense, especially with resistant pigweed. We will need to examine all inputs carefully.”
“And consider whether it’s affordable,” Osborne says. “In a tough production season, is it worth the cost?’