What is in this article?:
- Prevention is best strategy for resistant weed management
- Prevention is key
- Identification of glyphosate resistance in the Texas High Plains is recent—2011.
- Dealing with Palmer amaranth—pigweed—is nothing new for the Texas High Plains.
- Most High Plains farmers relied on preplant incorporated herbicides before the Roundup Ready era.
Some of these weeds died as a result of spray application. The live plants also received the same spray application and are examples of resistant weeds.
Prevention is key
Prevention, Keeling said, is the best strategy. Keys to prevention include:
- Using herbicides with multiple modes of action.
- Using soil residual herbicides.
- Applying post-emergence tank-mix herbicide treatments.
- Using sequential weed control techniques.
- Going back to some tillage and cultivation.
- Adopting new technology.
He said residual herbicides such as trifluralin or Prowl are critical to preventing herbicide-resistant weed infestations. Incorporation, either through tillage or irrigation, is necessary, he said.
Those pre-plant materials are important to control small broadleaf weeds and annual grasses. “Rate will be relative, depending on soil types,” Keeling said. “Heavier soils may require higher rates. Higher rates also may be needed if the material is incorporated with irrigation.
“The value of yellow herbicide application is evident in the field,” he said. “Tumbleweeds, for instance, are controlled with yellow herbicides.
Pre-emergence residual herbicides, materials such as Caparol, Direx, Cotoran, Dual and Staple, “can help with weeds the yellows don’t control. On sandy soils, Caparol is the only one I’m comfortable with,” Keeling said. “North of Lubbock, any of the others will do.”
He said Dual Magnum and Staple may offer a broader spectrum of control than the dinitroaniline herbicides. “But we may have some residual issues with Staple.”
Postemergence treatments options include Staple, Dual Magnum, Prowl H2O and a few others. Some can be tank-mixed with Roundup.
In some cases, cotton weed control “has come full circle, back to post-direct spray applications at lay-by.” Product options include Caparol, Direx, Cotoran, and Layby Pro, applied alone or with Roundup. These treatments offer residual pigweed and morningglory control.”
New technology may be another key to delaying herbicide resistant weed infestations, Keeling said. GlyTol Liberty Link technology, for instance, is tolerant to Liberty and Roundup herbicides.” Tank-mixing those herbicides, however, is not effective because of an antagonism effect.”
Roundup is not as effective on morningglory but does a better job on pigweed than Liberty. “If a farmer has both weeds a sequential approach is best,” Keeling said. “If morningglory is the worst problem, apply Liberty first then follow with Roundup.”
He said dicamba with glyphosate offers improved control of problem annual and perennial weeds as a burndown or as an in-season treatment. “It’s especially helpful with glyphosate-resistant pigweed.”
New technology with tolerance to dicamba and glyphosate may pose some drift issues, Keeling said. Nozzle selection may help. He recommends coarse to very coarse spray and ground-only application.
He said a new technology, Enlist weed control system, which enables plants to have tolerance to 2, 4-D, may be approved for corn and soybean production in 2014. Approval in cotton may be 2016. Keeling said trials have shown “no significant injury to cotton.”
But he expressed concern with drift with either the dicamba or 2, 4-D products.
Tillage practices also may play a role in herbicide resistance management, Keeling said. “Conservation tillage protects the soil (and seedlings) from blowing, but it complicates weed control. Weed control, residue management and stand establishment are all considerations with conservation tillage. It is important to kill small weeds.”
Keeling said identifying glyphosate resistant weeds in the Texas High Plains was not a welcome event but not necessarily a surprising one either. A history of battling Palmer amaranth and following sound weed control programs delayed the onset of resistance to some degree and cotton farmers’ experience with controlling pigweed at least gives them a head start on managing the problem
And new production techniques and technology will aid their efforts, Keeling said.