- Resistant barnyardgrass major problem in Mid-South rice fields.
- Computer model shows how to address the weed.
- Yellow nutsedge work also ongoing.
COMPUTER MODELING done by weed researchers has shown the best way to tackle resistant barnyardgrass. ““We want to understand how to best protect technologies and herbicides within rice and other crops,” says Jason Norsworthy.
What if a producer does use just one mode of action until resistance builds up?
“The problem with that is the soil seedbank. By the time resistance is confirmed, the seedbank is extremely high. What happens is resistance to the next herbicide used occurs quickly due to the high seedbank.
“BASF is developing Provisia rice (ACCase-resistant), which will likely be available in three to four years. If we let all this ALS resistance build up with the belief that the ACCase chemistry will be the answer, we’re mistaken. Once resistance builds to one mode of action the chances of more resistance developing is very high.”
And in some Mid-South fields, Provisio rice may not be an option even before it’s released. “Jason Bond, (Mississippi State University weed specialist), has been working with a population of barnyardgrass that is resistant to ACCase, ALS, propanil and Facet. That’s shocking and makes you wonder how the producer can control the weeds. Think about it: this population is already resistant to the herbicide to be used with Provisio rice and that hasn’t even hit the market yet.” The selection pressure on this population likely came from applications of Ricestar HT or Clincher.
While working on the models, the researchers also found continuing confirmation of the value of diversity in weed control. But diversity only goes so far, warns Norsworthy. “It has to be done properly. You mustn’t use diverse herbicides at the wrong time, make applications to weeds that are too large. Otherwise, your program isn’t sustainable and resistance builds up.
“Even when using two modes of action, if you mistime the applications, the weeds will react in ways you don’t want. So, proper application timing is just as important as diversity.”
Clomazone under rice is essential at planting because “use of clomazone means the risk of evolving resistance to postemergence herbicides diminishes tremendously. So, you need a strong program at planting like clomazone or Command.”
Asked if the weed resistance message has gained full traction in the agriculture community, Norsworthy was positive. “Whether rice, cotton or soybean, I think it’s getting easier to get the message to stick. Farmers are more and more understanding and becoming part of the solution than the problem.
“But it wouldn’t be true to say all is well. Thirty percent of the soybean growers in the Mid-South are still using Liberty-only programs. Well, the good news is that 70 percent of the growers understand the real risks of weed resistance and are doing what they can to mitigate it.”
“Maybe it’s a mirror of society as a whole. Regardless of profession, some people are on top of their games and excel and push for better. Others barely get by.”
Will we ever get to the point where everyone is on board with preventing resistance? “No. One reason is that some producers seem overly optimistic that there will always be an answer provided when things get rough. Too often we’re reactive rather than proactive.”