By Emily Unglesbee
DTN News Intern
LAWRENCE, Kan. (DTN) -- University of Tennessee weed scientist Larry Steckel is warning growers they may need to get creative with spring herbicide burndowns.
"You're going to have to mix and match a little more than before," Steckel told DTN. "Roundup and dicamba has been the standard for the last decade, and that's not going to be the case this year."
For the second year in a row, growers across the country are seeing shorter supplies of dicamba, a herbicide many rely on to knock down challenging winter annual weeds such as horseweed (marestail) before spring planting.
Steckel said the shortage is a two-headed beast.
"The two biggest issues are demand -- there's a lot more marestail out there -- and this new paradigm in the chemical industry to not overproduce herbicides and then have to carry that supply over from year to year on the books," he said.
The fact that new dicamba-resistant traits in cotton and soybeans are on the horizon might also have prompted companies to limit their supplies of current dicamba formulations, Steckel speculated.
"The formulation of dicamba that you're going to be allowed to spray over top of those crops is going to be specified on the label, and it's going to be one of these new, improved formulations that isn't as volatile and stays put after you spray it," he explained. "So if you've got a bunch of the old (formulation) out there, even if it works pretty well, if it's not going to be labeled for use on those crops, you might have a hard time finding a home for it."
The demand side of the equation is unlikely to improve, Steckel noted. "We've been running out of herbicides a lot lately, and it's just because we've been using so many to combat these glyphosate-resistant weeds," he said. He referenced recent shortages in other herbicides such as Valor, Direx, Cotoran, and Diuron herbicides, the result of growers struggling to control weeds such as pigweed and waterhemp in addition to marestail.
The recent northern creep of herbicide resistance could stretch all herbicide supplies farther than ever this year.
"In Illinois and Indiana, marestail is blowing up there in a big way, and Palmer amaranth and waterhemp, too," Steckel noted. "So I expect these shortages to get more acute, because when you start trying to cover the big acres up there, that's a pretty big draw on a lot of these herbicides. I wouldn't be surprised to see a lot of herbicides get short this year because a lot of those farmers aren't going to get away with just Roundup anymore."
University of Illinois weed scientist Aaron Hager said as glyphosate-resistant marestail takes off in his area, he has seen an increase in the use of dicamba in fall burndowns, but it is less popular for spring burndowns.
"We don't use nearly the amount of dicamba for burndown prior to planting as folks in Tennessee use," he told DTN in an e-mail. "Most of the dicamba used in Illinois is as a postemergence application in corn. The dicamba (Clarity) label has some planting restrictions when using dicamba prior to planting soybean, and many folks in Illinois have been hesitant to use it as a burndown" in the spring.
For growers who do use dicamba to control winter annuals such as horseweed, primrose, henbit and purple deadnettle, the shortage will require some alterations. For now, Steckel said, growers can substitute or supplement dicamba in their burndown mixes with other herbicides like 2,4-D.
At rates at or above 1 pound per acre, 2,4-D can be as effective on horseweed as dicamba, but many cotton growers might want to explore other options, Steckel noted.
"In cotton-growing states, cotton farmers are very leery of 2,4-D, mostly because if you use it in the sprayer, it's awfully hard to clean out," he said.
Hager said 2,4-D remains one of the most popular burndown herbicide for Illinois growers, but increasing the rates requires a pre-planting interval adjustment. "Applying 2,4-D at 1 pound acid equivalent per acre generally provides better control of marestail compared with 1/2 pound, but most farmers here are reluctant to use this rate because of the increased waiting interval," he noted.
Other possible substitutes for dicamba include Verdict, Sharpen, Latigo, Gramoxone, and Liberty, Steckel said. Hager also recommended Saflufenacil, which works well on marestail.
The dicamba shortage is already straining other herbicide supplies, however. Verdict supplies are tightening and retailers could run low on Sharpen as well, Steckel said.
Alternative herbicides don't necessarily have the same plant-back dates, so growers must be very careful to check labels when adding new herbicides to their tank mix, Steckel stressed.
Growers facing a dicamba shortage should check with their Extension office for more localized recommendations on alternative herbicides and tank mixes.
For more details, see Steckel's discussion of effective tank-mixes that work around the dicamba shortage: http://news.utcrops.com/…
Emily Unglesbee can be reached at firstname.lastname@example.org
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