Smooth Scouringrush with Dr. Mark Thorne


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Episode Transcription:

Drew Lyon: Hello. Welcome to the WSU Wheat Beat podcast. I’m your host, Drew Lyon, and I want to thank you for joining me as we explore the world of small grains production and research at Washington State University. In each episode, I speak with researchers WSU and the USDA-ARS to provide you with insights into the latest research on wheat and barley production. If you enjoy the WSU Wheat Beat podcast do us a favor and subscribe on iTunes or your favorite podcasting app and leave us a review while you’re there so others can find the show too.

[ Music ]

Drew Lyon: My guest today is Dr. Mark Thorne. Mark studies weed management in agricultural crops in Washington State. He’s originally from northeast Oregon and now works in the Department of Crop and Social Sciences at Washington State University. His current focus areas are control, smooth scouringrush and rush skeletonweed in wheat-fallow systems and seed shatter, and Italian ryegrass, all serious problems with the cropping systems where they occur. Mark’s goal is to find effective methods to manage these weeds and reduce their negative impact on the crops grown. Grower inputs and the environment. Hello, Mark.

Mark Thorne: Hello, Drew.

Drew Lyon: So we’re going to talk scouringrush today, a weed that I wasn’t very familiar with when I arrived here in the PNW in 2012. Can you tell our listeners a little bit about where smooth scouringrush is occurring in Washington State?

Mark Thorne: Yes. And this is, you know, kind of a new weed for me in the past few years. But it is a native species to North America and Washington state. It primarily occurs in the central and eastern counties, but does occur in some of the western counties of the state, and primarily in areas where there’s some water that it can reach it and doesn’t grow well in sand dunes or, you know, dry, dry clay hilltops. But if it can find some moisture at some point down in the profile, it seems to persist quite readily.

Drew Lyon: And, you know, it’s one of several equisetum species, I think, in the state. And yet it’s the only one that seems to be causing problems in wheat fields. Is that true or yes?

Mark Thorne: Well, there’s… right. You’re right, there are several. There’s the field horsetail, the acquisition of more events. And then there’s another and it looks more like a little Christmas tree or a bush or is the scouring rush is a straight-up vertical stem. There’s another closely related species Equisetum hyemale scouring rush is also a smooth, upright stem. No very little branching, but it tends to occur in more wet areas than the smooth scouringrush the acquisition lambic made him that we’re working with. In crop systems, there is some issues in areas with the field horsetail. But out in the areas where we’re doing our work in the drier areas in central and eastern Washington, we’re finding that the smooth scouringrush seems to persist in particularly fields that have been in no-till farming or direct farming for the past for say 20 years.

Drew Lyon: Okay, so so what issues does smooth scouringrush present to farmers?

Mark Thorne: Well, it seems to be fairly persistent once it gets established, so the patch is always going to be there year after year in the same area and will spread to one of the main problems that it can inflict on crops is that it takes up space. It’s in pulse crops like chickpeas or lentils. It can actually have a more serious yield reduction in, say, crops like winter wheat that are a bit more competitive. So there, there can be a yield loss associated with smooth scouringrush. But there are also I’ve talked to growers that have had thick patches of it and so dense that it essentially plugs up the sickle bar on their combines. Another issue that it can happen with it is that it can it’s you know, at the time of harvest, especially wheat harvest or any harvest, I guess, it will impart moisture and to the crops so it can raise the moisture content of the wheat being harvested. It can also impart green coloring to the coats of chickpeas, which reduces their quality.

Drew Lyon: Okay, so it impacts it in several different ways.

Mark Thorne: Yeah.

Drew Lyon: Okay. And what control strategies have you been looking at and found to be most effective? And how can these be used by farmers?

Mark Thorne: Well, the research on control has gone back a number of decades prior to our work. Dr. Don Till at Idaho found that chlorsulfuron on was an effective herbicide treatment on the smooth scouringrush chlorsulfuron as a group-two herbicide sulfonylurea. And the problem with that herbicide here in the annual cropping area is that it has, you know, 36 to 48 months plant back period for pulse crops. So it doesn’t fit well into a diverse annual rotation. It does fit well into any rotation that is primarily wheat, either wheat, winter wheat or spring wheat with a fallow period. And that can be applied during the fallow period as Finesse®, the product Finesse®, or it can be applied in the crop as the product Finesse® or the product Glean®. And that can be that can actually provide several years of reduction in stem density. The one issue of applying it in the crop is that in winter wheat, the herbicide timing of application is usually prior to the stems emerging from the ground. So it may miss at that point. But another option that we’ve we’ve been looking into is the use of a glyphosate product, RT 3, at a higher labeled rate than than than is most frequently applied, where we’re applying up to three quarts of the material per acre on these patches and finding that when if we include an organelle silicone surfactant, in our case, we started out with a product called Silhouette L77, that were actually getting control into the next couple of years. It’s been fairly consistent. We’ve had a couple of times when it’s not been as consistent as we had hoped. But it’s actually much more effective than applying the RT 3 just by itself or with some of the standard surfactants that have been applied or added these to this product in the past. And I think the other thing, too, is in the, you know, in the fallow period when we’re applying this, the stems are upright and green. And, you know, easily, you know, there’s a lot of surface area to take up the herbicide.

Drew Lyon: Yeah, I was going to ask you when you were applying it, but in fallow during the summertime when the plants are actively growing.

Mark Thorne: That’s correct. And we’ve applied anywhere from, you know, in the latter part of May when the stems are just getting up kind of at their, you know, at their height that they usually are at anywhere from, oh, you know, 16 to 24 inches is the typical canopy height of smooth scouringrush in these fields. And we’ve applied, you know, all the way through August. And, you know, we’ve gotten fairly consistent results. Like I said, there’s been some applications that didn’t work as well as others. And that’s another, you know, a question for research, certainly.

Drew Lyon: Okay, so both those herbicide products you mentioned, glyphosate and chlorsulfuron have some history of having resistance development in the weeds treated. Is that a risk here with a smooth scouringrush? If we rely on just chlorsulfuron as either Glean® or Finesse® and glyphosate and whatever product we buy that we’re just going to create a resistance issue down the road.

Mark Thorne: So, fortunately, the species reproduces and spreads primarily vegetatively. So there’s less chance for the development of resistance through, you know, gene recombination. And the window for sexual reproduction in this species is quite narrow and limited to conditions that are, you know, cool, wet soil, muddy soil. And that and that situation doesn’t really occur much in the cropping areas that we’re dealing with. So to make a long story short, it’s really unlikely that unlike other species, like russian-thistle, that we’re going to see resistance to something like chlorsulfuron.

Drew Lyon: Or even glyphosate.

Mark Thorne: Or glyphosate.

Drew Lyon: Okay, well, that’s good news. So this species are these species particularly smooth scouringrush, because that’s when we’re talking about has been around for a very long time. So it’s a survivor. We’re probably not going to be able to figure out how to eliminate. Are there any good things that come from smooth scouringrush?

Mark Thorne: Yeah, that’s a that’s an interesting question because it has been here, the species— the the the equisetum and genus has been around Theroux’s roughly 350 million years. Back to the days of the dinosaurs. And so it’s had a role in the development of, you know, feeding dinosaurs, creating carbon reserves that eventually turned into coal or petroleum products these days. So there’s you know, there’s that history. There’s a different equisetum genus that occurs in the Arctic. And they’ve actually found that it cycles nutrients from deep in the soil because these species have the capability of rooting very deep. And so it’s actually been shown to pull elements like phosphorus from deep in the profile up to the surface. I don’t know if that’s occurring with smooth scouringrush in our cropping systems, but, you know, it’s certainly a possibility and the other, you know, potential use this plant, the stems contain up to about 25% silica. So, you know, if you’re looking for a natural scrubbing material that you can clean your, you know, your dirty pots with. I think this might be a good, good candidate.

Drew Lyon: [ laughter ] And hence its name, right? That’s why the pioneers gave it the common name of scouring rush, or smooth scouringrush.

Mark Thorne: Correct.

Drew Lyon: So research continues with on this weed. And what kinds of things are you doing at this stage?

Mark Thorne: Well, we’re we’re combining RT 3 glyphosate with the Finesse®. And we’re finding actually that’s probably going to be a better treatment as a combination than the either the two products by themselves. We’ve we put out trials last year and near Dayton and near Steptoe, and we’ve put out another trial this year up near Rearden. And finding similar results so far. The downside of this research is we don’t really know the full effect of the application until a year following treatment. So it’s always, we put it out and then hold our breath for another year and then and then see what you know, what happens. There’s a lot of physiologic or physiology questions that could be asked with this species because there’s you know, it’s not a modern plant and it sometimes doesn’t behave like modern plants when it comes to especially herbicide use.

Drew Lyon: Okay. If people want to learn more about your research, is there someplace they can go to to find out about that?

Mark Thorne: Well, I think we’ve got some annual reports on the Small Grains website for crop and soil science.

Drew Lyon: Yeah, I think that’d be a good place for And sounds like you’ll have some more of those in the next report that comes out usually when in early January. Mark, thanks for coming on and sharing your work on smooth scouringrush with our listeners. I think it’s a weed that there’s actually quite a bit of interest in and a lot of people scratching their heads about how to go about controlling it. So thank you.

Mark Thorne: Thank you, Drew.

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Drew Lyon: Thanks for joining us and listening to the WSU Wheat Beat podcast. If you like what you hear don’t forget to subscribe and leave a review on iTunes or your favorite podcasting app. If you have questions or topics, you’d like to hear on future episodes please email me at drew.lyon — that’s –( You can find us online at and on Facebook and Twitter @WSUSmallGrains. The WSU Wheat Beat podcast is a production of CAHNRS Communications and the College of Agricultural, Human and Natural Resource Sciences at Washington State University. I’m Drew Lyon, we’ll see you next time.

The views, thoughts, and opinions expressed by guests of this podcast are their own and does not imply Washington State University’s endorsement.