What Farmers Need to Know About Herbicide Resistance in Rice with Dr. Jason Norsworthy
One of my favorite lines from my conversation with Dr. Jason Norsworthy came pretty early when he said, “I have never met a weed I liked.” I laughed because I think just about every farmer can relate to that. We spend a lot of time watching weeds. We scout for them, spray for them, worry about them and sometimes wonder how in the world that one plant survived when everything around it died. And that one surviving weed may be telling us more than we realize.
Dr. Norsworthy is a weed scientist and professor at the University of Arkansas, and we spent our conversation talking about herbicide technology, resistance, new products coming to the market and what farmers can do now to protect the herbicides we depend on. We talked a lot about barnyard grass because, as rice farmers know all too well, it can be one of our biggest challenges. Barnyard grass is aggressive. It grows fast, produces a tremendous amount of seed and, in some fields, has developed resistance to more than one herbicide site of action.
That is where the problem can get away from us in a hurry. One plant survives an application, that plant produces seed and those seeds become next year’s weeds. Before long, what looked like a few escapes can become a much bigger problem across the field. That really drove home one of the biggest points of our conversation: resistance management has to begin before we have a full-blown resistance problem.
Dr. Norsworthy also explained something I think is important for farmers to understand. Changing herbicide products does not always mean we are actually changing the way we are attacking the weed. We hear the terms “mode of action” and “site of action” a lot. Mode of action describes how the herbicide affects the plant, while the site of action is the more specific target inside the plant. For practical purposes on the farm, the important thing is that just because the jug has a different name on it does not necessarily mean we are putting different pressure on that weed population. Simply mixing two herbicides together does not automatically solve the problem either. Both products need to actually be effective on the weed we are trying to control. Understanding what we are using, and why we are using it, matters.
Another point that stuck with me was the importance of keeping weeds from ever getting established in the first place. The best weed may very well be the one that never comes up. Residual herbicides are a big part of that strategy. If we can control weeds before or just as they emerge, we are not only keeping them from competing with the crop, we are also keeping them from producing more seed.
Timing matters too. We have all seen what happens when a weed gets just a little too big before we get across the field. Control gets harder. Sometimes we get partial control, and sometimes we leave survivors behind. Dr. Norsworthy also talked about the importance of getting rice flooded as early as practical. A good flood is another tool we can use to suppress weeds and take some of the pressure off our herbicide program. Every weed we keep from making seed is one less weed we have to deal with later. It sounds simple, but it may be one of the most important things we can do.
We also talked about new herbicide technology coming for rice, and there are some exciting developments. Dr. Norsworthy discussed products such as the seed treatment safener called Viludo and new herbicides including Canali and iptrizopyrid. Canali, based on tetflupyrolimet, is especially interesting because it represents a new herbicide site of action. We do not get brand-new sites of action very often in agriculture. In fact, it has been more than 40 years since we have had a new site of action discovered, which tells you just how significant a new tool like this can be.
But new chemistry is not a free pass, and that may have been one of the most important messages from the entire conversation. A new herbicide can give us another option, but if we use it over and over until resistance develops, we are right back where we started. We have to protect the new tools just like we have to protect the ones that are still working today.
That means using residual herbicides, layering them when appropriate, rotating sites of action, rotating crops where we can, flooding rice early, scouting our fields and doing everything possible to keep weeds from going to seed. Crop rotation can make a real difference too. Moving from rice into a crop such as soybeans gives us access to different herbicide options and allows us to change the pressure we are putting on the weed population.
There was one other part of our conversation that I think more farmers should take advantage of, and that is testing. If you have a weed in a field that should have died and did not, do not automatically assume you know why. Get it tested.
Farmers can work through their county Extension agents to submit suspected resistant weeds for evaluation. Barnyard grass, weedy rice, pigweed, sedges and other problem weeds can all be tested. Depending on the weed, researchers may want seed heads from several plants across the affected area, along with information about the field and the herbicides that have been used there. That information can help determine what the weed is resistant to and, just as importantly, what may still work.
To me, that is information worth having before we spend more money spraying a product that may no longer control the weed in that field. And here is something else worth knowing: this testing is FREE because of funding provided by the Rice Checkoff that we all support when we sell our rice. I love seeing our checkoff dollars come back to farmers in such a practical way, especially when the information could help us make a better decision in the field.
The more I thought about our conversation, the more I kept coming back to one thing. We all want new tools. We want new chemistry. We want better options. And when something quits working, we certainly want another answer. But we also have some responsibility for protecting what still works.
That means paying attention to the escapes, knowing our fields, changing up our programs when we can and not letting one surviving weed become thousands. So when Dr. Norsworthy said he had never met a weed he liked, I completely understood. I do not think many farmers have.
But the goal is bigger than killing weeds this year. It is making sure we still have the tools to kill them next year and for many years after that. Because by the time herbicide resistance becomes obvious across a field, we are already behind.
The best time to manage resistance is before we get there.
See you in the field.