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Weed scientist: Two residuals better than one

Trying to cut costs by eliminating herbicides may not produce savings.

Forrest Laws

January 31, 2022

Rice farmers haven’t been enjoying the higher prices that producers of other commodities have, which means they may feel the sting of rising input costs more than other growers when they begin planting this spring.

Trying to cut costs by eliminating one or two pre-emergence herbicides, on the other hand, may not produce the savings they expect, according to Dr. Tommy Butts, Extension weed scientist with the University of Arkansas System Division of Agriculture.

Butts gave an example of how two pre-emergence or residual herbicides can be better than one, as University of Arkansas Extension weed scientists like to say, in a presentation filmed at the University’s Rohwer Research Station at Rohwer, Ark. The recording was part of the 2021 Arkansas Rice and Soybean Online Field Day.

“The first plot I would like to show you has an application of Command alone,” he noted. (In the trial, researchers were strictly looking at pre-emergence herbicides and the length of control they provide. No postemergence herbicides were applied in the plots.) “Those pre-emergence herbicides went out six or seven weeks ago so it has been quite a bit of time.

“On this heavy clay soil we used 1 quart of Command per acre, and we did get halfway decent grass control, especially compared to our nontreated plot. But we still have a lot of grass escapes, and Command is not good for broadleaf weed control.”

Weed spectrum

Butts said hemp sesbania or coffee bean had broken through “so we didn't get that diverse weed spectrum. And using only one mode of action plays into hastening the evolution of herbicide resistance. Command is a staple herbicide in our rice, and we want to prevent the development of resistance to Command in our barnyardgrass populations.”

The next plot Butts discussed received an application of Command and Facet or Quinclorac herbicide at 43 ounces per acre pre-emergence to provide two effective modes of action.

“By adding Facet into that mix we can increase the diversity of the weed spectrum we get,’ he said. “You'll notice it helped control a lot of our coffee bean. It will also give us a little flatsedge control and take out a few other weeds as well.

“This is one of my primary recommendations for our first residuals in rice. We see that Facet consistently works better as a residual, especially when pairing it with Command. I would rather get as much activity with it upfront as we can rather than saving it for postemergence where we often seen mixed results for controlling barnyardgrass.”

Another set of plots received Command and Prowl applied as a delayed pre-emergence application. Command was applied at 1 quart per acre and Prowl at 2.1 pints per acre after the seed had imbibed water.

“Again, you’ll notice good grass control from two effective modes of action, and Prowl brings a little bit of broadleaf activity to the table as well,” he said. “It’s not excellent by any means, but it did help us on some of those broadleafs.”

Butts also discussed plots that received Command plus Gambit and Command and Sharpen. Gambit was applied at 2 ounces per acre and Sharpen at 3 ounces per acre.

“The grass control is almost equal in these plots because pretty much all the work is coming from the Command on the grass control front,” he noted. “Gambit does a very good job on the coffee bean and is also good for yellow nutsedge and several other broadleafs.

“Sharpen is good on a broad spectrum of broadleafs. It will give us some rice flatsedge control but minimal yellow nutsedge control. So with Sharpen we can get rice flatsedge and with Gambit yellow nutsedge, and we can get broadleafs with both.”

Butts said he typically leans toward Sharpen in the first application, although Gambit may appear to provide better broadleaf weed control.

“That’s because if I use two ounces of Gambit pre-emergence I’ve used my season limit for the halosulfuron active ingredient, and I can no longer apply Permit or Gambit later in the season for yellow nutsedge escapes.”

For more on rice weed control, visit https://aaes.uada.edu/videos/2021-rice-weed-control/.

About the Author(s)

Forrest Laws

Forrest Laws, senior director of content for Farm Press, spent 10 years with The Memphis Press-Scimitar before joining Delta Farm Press in 1980. He has written extensively on farm production practices, crop marketing, farm legislation, environmental regulations and alternative energy. He now oversees the content creation for Delta, Southeast, Southwest and Western Farm Press. He resides in Memphis, Tenn. He served as a missile launch officer in the U.S. Air Force before resuming his career in journalism with The Press-Scimitar.

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