The recent ruling by the 9th U.S. Circuit Court of Appeals that forced the Environmental Protection Agency to revoke its approval for dicamba-based chemicals such as Engenia, FeXapan and Xtendimax has some producers racing the clock with their herbicide applications.
In Oklahoma, existing stocks of the three dicamba products may be applied to Roundup Ready Xtend cotton and soybeans through July 31, provided a producer or commercial applicator was in possession of them on June 3, the date the court’s decision took effect.
“Producers are wondering what their options are if they haven’t already purchased dicamba or need to make an application after July 31,” said Todd Baughman, weed science program leader for Oklahoma State University’s Institute for Agricultural Biosciences in Ardmore.
“For those growers that had already purchased one of those three products, they still have the option to use those herbicides. However, if they don’t have enough of the product, they’ll have to look at another option to cover all their acres,” he said.
Currently the following products are labeled for over-top application in Roundup Ready XtendFlex cotton:
- Tavium - A premix of dicamba and metolachlor.
- Liberty and Roundup – These non-selective herbicides are active on a wide range of weeds.
- Staple – This product provides postemergence as well as residual control on several broadleaf weeds.
- Dual Magnum, Outlook and Warrant – These can be applied after cotton is up but will not control weeds that have emerged at the time of application. Also, rainfall or irrigation is needed to move the herbicide into the soil profile to control weeds that have not yet emerged.
- Assure II, Fusilade DX, Poast and Select – These products will control most grass species when applied postemergence but do not act on broadleaf weeds such as pigweed.
“The concern with Roundup is the number of fields that have weeds resistant to the herbicide,” Baughman said. “Timing is critical on all weed species with Liberty, especially pigweed and grasses. We have consistently observed inadequate control when applications are made to larger weeds.”
Timing based on weed size is vital for postemergence control with Staple. Many weeds require applications to be made before the weed is taller than 2 inches. Staple is ineffective on weeds resistant to ALS inhibitors.
“Considering the current supply restrictions on Engenia, FeXapan and Xtendimax, it is probably a good idea to tank-mix Dual Magnum, Outlook and Warrant herbicides with these existing dicamba products or one of the other postemergence herbicides if the label allows,” said Gary Strickland, dryland cropping systems specialist with OSU’s Southwest Research and Extension Center in Altus.
Cultivation or hand weeding is a final option to control troublesome weeds in cotton. Always refer to herbicide labels for restrictions, weed size, crop stage, use rates, tank mix partners and herbicide adjuvants, OSU experts said.
Tavium, Roundup, Assure II, Fusilade, DX, Poast and Select are currently labeled for over-top applications in Roundup Ready Xtend soybeans, as are the following additional herbicides:
- Cadet, Cobra, ET, Reflex, Resource and UltraBlazer – Protoporphyrinogen Oxidase or PPO herbicides are active on many broadleaf weeds in Oklahoma.
- Classic, FirstRate and Pursuit – These ALS herbicides are active on several broadleaf weeds in Oklahoma, providing postemergence as well as residual weed control. Timing based on weed size is important for postemergence control and some populations of Palmer pigweed and tall waterhemp are resistant to this class of herbicides.
Producers who have not planted soybeans yet may want to reevaluate their current preemergence program, Baughman said.
“A preemergence herbicide program that contains two or three different active ingredients may be the most effective option this year,” he said. “Growers may want to consider adding a residual herbicide to their postemergence applications to improve season-long control. Also, be sure to read labels for preharvest and crop rotation intervals.”
For growers who need two post-emergence applications but have only enough dicamba for one application, Baughman said they should consider applying Liberty in cotton or a PPO in soybeans first. For producers who plan to use the Xtend product first, tank-mix Dual Magnum, Outlook or Warrant.
“Producers should contact their OSU Extension county agricultural educator to discuss options that best fit their specific operations and available resources,” Baughman said.
The OSU Institute for Agricultural Biosciences and OSU Southwest Research and Extension Center are part of the university’s Division of Agricultural Sciences and Natural Resources, comprised of the Ferguson College of Agriculture and the university’s two state agencies: OSU Extension and the Oklahoma Agricultural Experiment Station system.