Timing and coverage are "critical," as cotton and soybean growers look to alternative dicamba herbicide applications, said Todd Baughman, Oklahoma State University Extension weed scientist.
"Where we're dealing with resistant weeds, my biggest concern is what options we have, and how timely those applications have to be with some of these other technologies to make it work," Baughman said.
In cotton, from a broad spectrum standpoint, growers are limited to the herbicide Liberty. "That one can be hit or miss in the Southwest due to our drier climate and lower humidity. It doesn't work as well as it does in some other parts of the country, especially with pigweeds, which is the number one species we're dealing with," he said.
June 3, the Ninth Circuit Court ruled to vacate the federal registration for three dicamba products, Xtendimax, FeXapan, and Engenia. June 8, an EPA order clarified the ban, stating that cotton and soybean producers or commercial applicators are allowed to use existing stocks as long as they were in possession on June 3, the date the court's decision took effect.
Although cotton and soybean producers in his state are disappointed with the ruling as well as the timing, Baughman says there are alternatives.
"With Liberty, we can do some good, but timing is critical to making it work," Baughman said. "The weeds need to be less than 4 inches tall."
Soybeans, though they don't have the Liberty link gene in them, are Roundup and dicamba-tolerant. "So, Liberty's not an option on those acres that have already been planted or seed's been purchased and going to be planted. That leaves the PPO set of herbicides like Reflex, Cobra, Blazer."
PPO or Protoporphyrinogen Oxidase is the mode of action that these herbicide use to control weeds, he said.
With PPOs, timing is crucial, but before a grower applies them, there are some things to consider. "With Reflex, depending on your cropping system, there are rotational concerns. In Oklahoma, we know we have some pockets of potential PPO resistance, so that takes away Reflex in those areas.
"There's not a lot of options. Hopefully, if they knew they had that problem they can either bump up their preemergence program or hopefully they already have," he said.
Soybeans are at an advantage over cotton as they have yet to be or are in the process of being planted. "They don't have to switch but can use a better preemergence program upfront on those acres. But on our cotton acres, most of those are in the ground, so there's not an option to adjust your preemergence program because you didn't know you weren't going to have that technology. But like I said, we can do some good with Liberty, but timing is critical."
Coverage is also essential. "To maximize the activity out of some of these other products, make sure there is thorough coverage on these weeds," he said.
To increase coverage, consider nozzle selection, pressure and upping the gallons. "Check the label and see the recommendation on the label of the various products and what it recommends from a gallons per acre standpoint."
For growers who had dicamba in their possession as of June 3, and know they're going to need two post-emergence applications, consider applying Liberty (cotton) or PPO (soybean) first , "especially if they know they only have enough dicamba for one application. Even though timing is critical for both of these products, it's a lot more critical with these herbicides than with the Xtend products."
Baughman also recommends including a residual like Dual Magnum, Outlook or Warrant. "If they're going to run the Xtend product first, tank-mix one of those to give them some additional residual."
Soybeans often only require one dicamba application. "Go ahead and run it because you don't have the Liberty option and include a residual product to help maximize control – this has been our standard recommendation even before this ruling," Baughman adds.
As moderate to severe drought continues to threaten production in the Texas and Oklahoma Panhandles, a lack of rain and, therefore, fewer weeds may be the silver lining.
"I guess on a positive note, the lack of moisture has helped us a little from a weed standpoint," he said
But overall, producers and many in the agricultural industry are disappointed with the ruling.
"We would have been troubled by this decision no matter what, but I think the timing has probably upset people as much as anything. There wasn't even an opportunity to change plans. They feel like it's unfair to handcuff them after they have already purchased or planted that technology."