Caution is key in using new herbicide systems
by PAUL HOLLIS
Promising new herbicide technology could give Alabama farmers a powerful weapon in their battle against pigheaded pigweed, but growers must be alert to the chemicals’ negative impact on nearby crops.
The new herbicide-resistance systems—a key topic during the recent Central Alabama Crops Tour at the E.V. Smith Research Center in Shorter— include Dow AgroSciences’ Enlist, and Xtend from Monsanto and BASF. The systems allow farmers to spray specific formulations of herbicides over crops such as corn, soybeans and cotton without damaging the crops.
While the seed containing the resistance traits has been deregulated and is available in commercial crop varieties, registration of the herbicides that have been formulated specifically for use on the crops is still pending EPA approval.
The new herbicide-resistance traits have the potential to help farmers control many problematic broadleaf weeds, including pigweed, morning glory, marestail, ragweed, sicklepod and cutleaf evening-primose. They also provide new tools to control glyphosate, ALS and PPO-resistant pigweeds that are present throughout the Southeast, said Steve Li, assistant professor in the Department of Crop, Soil and Environmental Sciences.
Although research trials in Alabama this year have shown good results with the technology, spray drift, vapor movement, or volatilization, and potential off-target injury are raising concerns among extension specialists, county agents and growers.
Cotton is extremely sensitive to 2,4-D—a herbicide used in the Enlist system—while soybeans and peanuts are more sensitive to dicamba, which is part of the Xtend system. Many vegetable and fruit crops also have low tolerance to the herbicides, Li said.
“To reduce off-target injury, using the correct spray nozzle tips, spray settings and favorable environmental conditions is absolutely required during the application of these herbicides,” Li said. “Misapplications to non-tolerant varieties and insufficient tank cleaning also can be devastating due to high crop sensitivity.”
The new formulations of 2,4-D and dicamba are expected to be less volatile than previous formulations, but growers still should take every precaution when using them, Li said. If the wind is blowing to sensitive crops nearby, these herbicides should not be used at all. Commercial applicators who use the same sprayer for multiple crops and fields are exposed to a higher risk of cross-contamination when these new technologies become commercially available.
Wykle Green, a weed science graduate student, says quality weed control will take time, so growers should slow down their tractors or sprayers and make sure they’re getting adequate coverage, especially when pigweed is growing tall.
“We can’t predict when or if the new herbicides will be labeled for use, but if they are, hopefully the labels will give us several options of spray tips and tank mixes,” Green said.
The main concerns when spraying are volatility and drift, he said. “We need to pay attention to spray nozzle size, gallons per acre and wind speed when we’re spraying.”
He recommended coarser nozzles, too.
“We looked at different spray nozzles, going from the finest, smallest droplet size to the coarsest, and the coarsest works best,” he said.
Thoroughly cleaning out spray tanks is also important, he said.
“If you just sprayed a full tank of dicamba-resistant cotton across the road, and you have non-resistant soybeans in another location, you can’t just drain the tank, fill it with water and spray the soybeans,” Green said. “Using a detergent-based cleaner and triple-rinse program will be a must before spraying sensitive varieties, but more research is needed to evaluate clean-out efficacy and the potential risk of cross-contamination in commercial sprayers.”
Researchers are looking at the yield effect of small rates of drift on non-dicamba soybeans, he said, noting that a half-million acres of crops in the MidSouth were affected this year by off-target damage from dicamba herbicides on non-dicamba-resistant crops.
“If we don’t do a good job of stewardship with these new products, we might not even get a label,” Green said. “It’s important that we take all the precautions we can, and that we be aware of our surroundings and of our neighbors.”
It’s also important, he said, to use different herbicide modes of action and not rely on just one new technology.
“We’ve made this mistake with the glyphosate-based systems for the past 20 years,” Green said. “We need to do a good job of putting out strong pre-emergence herbicides, overlapping our residual herbicides, and using this newest technology as one option in our toolbox.”
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