Growers turn to decades-old chemistry to fight ALS-resistant rice flatsedge.
By Vicky Boyd
Every time Ricky Posey and his stepbrother, Joe Ray Melvin, looked out their shop door near Hunter, Ark., they saw a big patch of ALS-resistant rice flatsedge that was a constant reminder of their problems.
After taking the field out of rice and putting it in pasture, the problem returned when they planted rice again.
“You’d think that the sedge would disappear, and it was still there when we put it back into rice,” Melvin says.
Not only does the flatsedge reduce rice yields through competition, but it also lodges, taking down nearby rice with it and creating harvest losses.
Melvin had talked to relatives near Crowley, La., who had used League herbicide from Walnut Creek, Calif.-based Valent U.S.A. last year. So he says he and Melvin decided to try it this season. League, which contains the active ingredient imazosulfuron, is labeled for a wide variety of broadleaf, aquatic and sedge weeds in rice.
At the suggestion of their Valent rep, Mike Morris, Melvin and Posey added 4 pints of Bolero herbicide to the 4 ounces of League they put out at delayed pre-emergence using a ground rig.
As of mid-June, they could not find a single rice flatsedge in the field of Roy J by their shop nor in any other field where the weed had been a problem.
But Melvin and Posey aren’t the only growers who have gone back to the future by incorporating the 40-plus-year-old Bolero from Valent into their weed-control program.
Demand for Bolero grows
Bob Scott, University of Arkansas Extension weed scientist based in Lonoke, says most Arkansas rice fields this season look clean. He attributes it to growers getting the message of overlapping residual herbicides and applying them early to prevent weeds from germinating and becoming a problem.
“Our base program that we’re commending is either RiceBeaux or a make-your-own RiceBeaux with propanil and Bolero very early post,” Scott says. Then growers should return pre-flood or very early post-flood with Basagran and propanil or crop oil concentrate
He says some growers this season also have had success with Sharpen as a follow-up second treatment, but it can injure rice, especially if tankmixed with another herbicide.
Growers must have listened to Extension because demand for Bolero this season exceeded supply, Morris says. As a result, some growers turned to RiceBeaux, a premix of thiobencarb and propanil from RiceCo. Thiobencarb also is the active ingredient in Bolero.
“This ALS-resistant flatsedge is a growing issue in the Mid-South,” Morris says. “Everybody has got some of this in some place on their farm–some more than others.”
The ALS class of chemistry, which belongs to the Weed Science Society of America’s Group 2, includes Newpath, Beyond, Grasp, Londax, Regiment, League and Permit herbicides. Bolero, on the other hand, belongs to Group 8.
Weed surveys conducted by the University of Arkansas and Mississippi State University have found ALS resistance widespread in rice flatsedge (Cyperus iria L.) populations in the respective states. Although the resistance problem also has been confirmed in Louisiana, it is not yet widespread, according to Louisiana State University weed surveys.
Scott says he and Arkansas colleagues assume that when rice flatsedge is resistant to one ALS herbicide, it is resistant to all members of the group. Screening has found a few populations of flatsedge and barnyardgrass are resistant to some ALS chemistries but not to Regiment or Grasp.
“But we pretty much assume they’re resistant to all of the ALSes,” Scott says. “I think because of the potential problems of cross resistance, you don’t want to run the risk of putting that first shot (of ALS) out and not having it work.”
A learning curve
Jackie Dobson, a crop consultant with Helena Chemical near Brinkley, Ark., has seen ALS-resistant ricefledge in many of the fields he scouts.
“In the past probably 20 years, growers have gone to zero-grade fields and it’s basically rice after rice after rice after rice,” he says. “We used Permit until we wore it out and things got resistant to it.”
This season, Dobson recommended Bolero as part of a tankmix program to many of his growers. But he admits the herbicide has a bit of a learning curve. You have to wait at least five to seven days after planting until the seed has imbibed moisture and has least a 1/8-inch sprout on it before application. If not, you risk reducing germination. You also have to avoid letting fields dry out to keep the thiobencarb active.
“This was a perfect year for Bolero because we kept getting those showers to keep it activated,” Dobson says. “If you don’t keep moisture on it to keep it active, the grass or escapes will come back.”
He also recommends using Helena’s propriety adjuvant, Grounded, which helps Bolero adhere to soil particles and keep it on the soil surface. Without the material, Bolero could be washed away with flushing or moved below the root zone.
For more information, read University of Arkansas’s publication, “Identification and Control of Problematic Sedges in Arkansas Rice,” http://www.uaex.edu/publications/pdf/FSA-2173.pdf