Weed management researchers seek to improve the bottom line for soybean farmers

With variables like weather, insects and weeds always a danger, Louisiana’s soybean farmers can never rest easy.

But they can have some peace of mind knowing that LSU AgCenter weed scientists’ top priority is to improve their bottom line.

“From a producer standpoint, we’re trying to maximize yields in everything we do while minimizing production costs,” said Donnie Miller, John B. Baker Professor for Excellence in Weed Science. “When you have multiple variables that can attack a crop, such as bugs, weeds and disease, it would be great if you could make just one application through the field, applying insecticide, herbicide and fungicide instead of making three separate trips. You get the same benefits at a third of the application cost.”

At the LSU AgCenter Northeast Research Station in St. Joseph, Miller and his colleagues have been concentrating on the two latest technologies for weed management in soybeans, the Xtend weed control system, which allows growers to apply dicamba over the top of soybeans, and the Enlist cropping system that allows them to apply 2,4-D choline.

Miller conducted co-applications with Roundup Powermax and Xtendimax and a number of insecticides commonly used in soybeans. The same was done using the post-emergence herbicides Enlist Duo and Enlist One and Liberty. Both studies combined Dual Magnum and Warrant, which provide soil residual control of unemerged weeds (pre-emergence).

“Generally, with the post-emergence herbicides we tested, you rarely see any injury, but when you start adding things like Dual Magnum and the Warrant, they have compounds in their formulations that can heat up things that will burn the beans and speckle them up but rarely impact yield,” Miller said. “We found that adding the insecticides to the herbicides didn’t increase the injury we saw over what we saw with the herbicides alone, making these co-applications possible and saving one trip across the field.”

In a separate study, looking only at weed control without the insecticides, over-the-top applications were made with the post-emergence and pre-emergence herbicides, looking at timing variables.

“The problem you run into there is that the longer you let the weeds sit out there, the longer they’re competing with the crop,” Miller said. “If you let the weeds get too tall before the application and something like a storm hits, by the time you get back, you’re not spraying 2-inch weeds, you’re spraying 7-inch weeds, and they are a whole lot harder to kill.”

Miller also studied Enlist One drift impact to Xtend soybeans and if injury was exacerbated by the addition of the residual herbicide. He found it was not. His additional study of prickly sida management in both Xtend and Enlist soybean varieties reemphasized the benefits of timely management through application to small, actively growing plants of 1 to 2 inches in height.

“Unfortunately, when you’re farming 4,000 acres, timeliness is sometimes hard to accomplish,” he said. “So, if you have prickly sida in a certain area, it’s better to focus on making that application early or including soil residual herbicides at planting to control the sida or reduce its growth rate for a timelier application with the post-emergence herbicides.”

Finally, Miller and his crew looked at Reviton, a quick-acting herbicide that quickly desiccates green leaf and stem material on soybean plants. Ideally, soybean seed should be harvested at about 13% moisture. The moisture content when Reviton is applied at soybean growth stage R6.5 goes down from 50% to 13% quickly.

“Paraquat, or Gramoxone, is going to desiccate everything too, but you have to wait 15 days after the application to harvest per label requirements,” Miller said. “Reviton manufacturers are trying to get the time down to five to seven days instead of 15, thus lessening the chances of exposing them to rain during hurricane season.”

Daniel Stephenson, the Jack Hamilton Regents Chair in Cotton Production, statewide extension weed specialist and research coordinator at the LSU AgCenter Dean Lee Research Station in Alexandria, represents the flip side of the same coin of the state’s weed management research. He and Miller do similar crucial work, but regional soil variability makes them both indispensable to Louisiana soybean farmers.

“Donnie’s region has Mississippi River alluvial soil and a big chunk of what I deal with is Red River alluvial soil, which is vastly different,” Stephenson said. “What Donnie determines in the northeast might not apply to growers in Rapides, Avoyelles, St. Landry or Caddo parishes, and what I determine may not be applicable to Tensas, Madison and East Carroll.”

Stephenson’s primary focus is grass control, particularly in the dicamba-tolerant Xtend crops. He said Louisiana growers have had significant issues using dicamba to control grass. He has trials to determine why and what tweaks can be made to remedy the problem.

With this spring’s unprecedented rainfall, he couldn’t plant his soybeans until the last week of May, a month where the Dean Lee Research Station received 25 inches of rain. Still, like Miller, he remains undaunted in his overarching goal.

“The entire point of our research is to put as much money back in the growers’ pockets as we can every year, no matter the obstacles,” Stephenson said.

Effects of RevitonJPG

Reviton applied to R6.5 growth stage prior to harvest desiccates soybean foliage and stems at seven days after application. LSU AgCenter photo


Enlist Duo in Enlist soybean controls prickly sida when applied to small, actively growing plants and V1-V2 soybean early season growth stage. LSU AgCenter photo

Roundup PowermaxJPG

Roundup Powermax Plus Xtendimax in Xtend soybean, combined with insecticides, revealed no increase in injury over herbicides alone. LSU AgCenter photo

9/17/2021 8:24:42 PM
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