Russian-thistle weed resources
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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 from WSU and the USDA-ARS to provide you with insights into the latest research on wheat and barley production.
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My guest today is Dr. Ian Burke. Ian is the RJ Cook Endowed Chair of Wheat Research and a professor in weed science at Washington State University. Ian started working in weed science in 1999 and joined the faculty at WSU in 2006. His research program has focused on basic aspects of weed biology and ecology, with the goal of integrating such information into practical and economical methods of managing weeds in the environment.
Dr. Ian Burke: Hello, Drew.
Drew Lyon: So, I guess you and I both received just shy of $103,000 from the Washington Grain Commission in this current fiscal year for our weed science programs. What do these funds allow us to do that wouldn’t happen without the additional support?
Dr. Ian Burke: You know, the funds are really critical for a couple of different parts of our programs, right? So, over the last 20 years, there’s been a substantial decline in the number of new herbicides that are being introduced into our area. And many of the older herbicides that we conduct experiments with aren’t supported by companies–the research just wouldn’t occur without the [Washington] Grain Commission support, because there’s just not support from private industry for this research. And so that’s a really critical component of our programs that simply wouldn’t occur without the Grain Commission funding.
The other thing that occurs as a consequence of that funding is intensive sampling for weeds and evaluations of grower submitted samples. We still get something like 30 to 50 samples submitted per season. We’ve gotten a lot more efficient at assessing those samples for a whole host of resistances. And we like to pride ourselves on getting response back within just a few months on what that resistance is. The Grain Commission funding does that too.
But the best part about what we’re able to do as weed scientists is leverage the funding so we’re able to identify other sources of funding that we could use as match. We currently match at least one of our Grain Commission projects with Washington State Committee for Pesticide Registration funding, and that would also not happen without the Grain Commission funding. That’s a stipulation of that match, is that there’s Commission funding to support it. And so, the Grain Commission funding is–I’m working in a lot of different ways in weed science–the fundamental efficacy program, but in other aspects too.
Drew Lyon: And in my program, it allows me to work on weeds that are important here in Washington, but maybe not much outside. Smooth scouringrush is one I’ve been working on that I don’t think I’d be able to work on without the support of the Grain Commission. So, it allows us to do some things that wouldn’t get done otherwise because to get federal dollars, you have to address problems that are an issue at the federal level. And some of our weed problems are quite unique to the Pacific Northwest.
Dr. Ian Burke: It also allows for adaptive capacities. So, when a new problem arises, it often arises in a way that makes it difficult to respond with federal funding. It might take us years to get funding to work on a new problem. Whereas, you know, a farmer approaches us with a particular issue–I have several examples from just this year alone for weeds I’d never heard of and never had an experience with–but we have the people on staff because of this funding. We can respond and identify methods to control these new weeds. And that’s really powerful.
Drew Lyon: Well, a weed that I wouldn’t say is new, unless you go back to the late 1800s—Russian thistle is on a lot of growers minds this year. You drive around the country and you can see fields that are fairly clean, but you can also see fields that are just green with Russian thistle plants after harvest.
Let’s talk about Russian thistle. What are some of the issues around this weed and why maybe is it such a problem this year? Because there’s a lot of interest in that one.
Dr. Ian Burke: We’ve worked on Russian thistle really since we started here. It’s one of the primary weeds in the low-rainfall zone and we have research that goes on there. And so, it’s just naturally one of the primary weeds of both our programs. And I don’t’ know if I’ve ever seen a year quite like this one.
And I have to think it’s because of the heat, the early onset of summer temperatures in May really set Russian thistle up to succeed in a way it doesn’t normally have an opportunity to. It has a very unusual form of photosynthesis. So, you know, back in college and high school, I know we all learned about the C3 and C4 photosynthetic pathways and we all learned about the parallel veins on the corn leaf, and that’s supposed to be C4 photosynthetic pathway. And the photosynthetic apparatus is built around separation of several different chemical reactions.
That’s not how Russian thistle works. It’s got a subcellular localization of the C4 which is really unique and it enables it to be the most water use efficient weed I think we have. It also has a very hard woody sort of growth pattern later in the season. I think it develops a very thick cuticle. And if you’re not timely and catch it early, there’s just no way to get the herbicide into the plant. The plant has an overall growth form that really minimizes the ability for droplets to penetrate down into the canopy of the plant. So, you kind of combine all that together and it’s really the perfect weed for low-rainfall zone growth–and you combine that all together and I think that kind of explains some of the problems we’re seeing this year.
Drew Lyon: I know in my Extension talks I often talk about you’ve got to get this one early because once it’s established, it’s a monster. But as a small plant, it actually is a weakling but it quickly develops into quite the troublesome weed to control after that.
I also wonder whether this year our crops just weren’t as competitive, so [that] allowed them to get established and not have the competition. Winter wheat is normally pretty competitive with it, spring wheat less so. But a lot of crops, especially out in the dry areas, were really struggling and not as competitive as they might have normally been.
Dr. Ian Burke: I agree with that. The ability for that weed to establish early in sort of April and May and sit in the canopy in a way that you don’t necessarily see it, unless you’re scouting pretty intensively, is a real benefit for it. And then when you harvest you release it into an essentially no canopy environment. It’s able to grow and reproduce pretty quickly and there’s no real financial incentive to treat it in that situation, although management of any sort of seed it produces in my mind requires some action post-harvest. That’s the time to potentially go out and deal with it.
The trouble we have is that [there are] very few products where it can actually kill it in that sort of situation. A lot of the systems that I know of, you and I worked on and we’ve had experience with watching Aaron Esser up at the Wilke Farm attempt to manage these weeds, involved timely applications of pre-emergence herbicides going into the fallow and that minimizes the growth of the plants that might germinate later when the pre-emergence herbicides maybe don’t have as much activity. In my mind, that’s sort of setting us up for success in the crop where we’ve reduced the overall number of weed seeds that might be present in the system all the way back in the beginning in the fallow. So that’s how I started thinking about managing this particular weed.
Drew Lyon: Yeah, and you know, it’s interesting that the seed of Russian thistle isn’t what we normally think of for seeds, and generally it’s not considered to be long lived. Can you talk a little bit about that issue and why managing the weed so you don’t get much seed production is really key to this whole thing?
Dr. Ian Burke: Yeah, I think that’s the sort of the weakness of the species is that it doesn’t have a very long-lived seed. The seed are essentially sort of pre-germinated plants and they don’t last long in the environment. Amusingly, we have a heck of a time getting the seed to even germinate and grow in our greenhouses. There’s a very special procedure we have to go through just to get them established. So, you know, another example of how weeds are very well suited to growing in our fields, but then when we try and actually grow them in our greenhouse, we can’t do it.
But because that the length of that seed—the longevity of that seed–is so short, it is one that you can really target for [in] management of the seed bank, minimize the total amount of seed production. Hopefully your neighbors are doing the same so you don’t get new material rolling in on onto your well-managed fields. And then in just a couple of years you can usually see a pretty significant decline in the overall population.
Drew Lyon: After harvest this year, I went out to the Lind Research Station and as you drive along, you’d see one field that was just really clean, not much of anything out there. And then you look on the other side of the road and just a solid carpet of green, which looked to me to be mostly Russian thistle. How does how does a grower deal with that when maybe they do a good job but their neighbor doesn’t? And this is a tumbleweed, it does move.
Dr. Ian Burke: Yeah, it’s unfortunate. There’s not a really good way to deal with that sort of situation. One of my rural sociologist colleagues kind of compared it to the to the analogy of raking leaves, right? So, you rake your leaves in your yard every year and you take good care of it, and then one good windstorm and the guy next door who hasn’t raked their leaves, their leaves are now in your yard. And so, you don’t necessarily go to the next door neighbor and complain about them not raking their leaves. Although I would argue that we probably need to be cultivating the relationships to be able to do that, because this is a weed that can cross boundaries in this way. So, there’s some sort of structural issues I think we have to address because of the nature of how a weed like Russian-thistle spreads that I don’t think we do a very good job of.
A road is no boundary for Russian thistle. And so, it’s very likely that those two fields are connected by the wind as that Russian thistle breaks off and tumbles in the fall, it will go right–it’ll go downwind into the next field that might be weed free. So, you want to you do want to be prepared to have those kind of hard conversations about managing weeds that are upwind of you, so to speak. But I don’t know that I have an easy answer for that one.
Drew Lyon: That is difficult. I know Judit Barroso down in Oregon State is trying, in a limited area, to do some work with a group of growers have agreed to try to keep it under control and put up fences to catch it and do some things like that. It’ll be interesting to see what happens from that kind of perspective, but it’s not something growers can deal with just by themselves. Although the more they can do to control the seed bank, I guess the better.
Dr. Ian Burke: Interestingly, the research that Judit’s doing has yielded evidence that fences are no boundaries either because they’ll pile up on one side of the fence and then the next plants that come along can just tumble right over the fence. That does take numbers of plants to get to that point so anything we can do to minimize the total number of Russian thistle out there that might tumble is going to be a win.
Drew Lyon: Okay. I know in western Nebraska they could actually take down fences. They pile up and then you get a heavy, heavy, wet snow and then the fence comes down. So, they can be rather problematic.
I noticed in western Nebraska we had Russian-thistle, but it was always in association with kochia, so it was not the solid, homogenous group.
And we do have some kochia moving out. It tends to be in the basin, right? But it’s been moving out the last few years and that, you know, a lot of those plants are resistant to glyphosate. But a few years back we found that Russian thistle was as well. Do you want to talk a little bit about glyphosate resistance because that’s what a lot of growers have used in the past to control Russian thistle during fallow and that seems to be a less effective means all the time.
Dr. Ian Burke: Yeah, it’s unfortunate. You know, glyphosate has been a relatively inexpensive and very effective tool for years. I think there’s a couple of different options if you know for certain that you have glyphosate-resistant Russian thistle. And these days if you have thistle sort of down that 395 corridor, it’s likely Russian, it’s like it’s likely glyphosate resistant.
So, you know, we found alternatives like paraquat and old bromoxynil to be relatively effective. You know, there are rules governing how you can use those two herbicides. You want to make sure you follow the labels pretty closely for those. They’re not as inexpensive as glyphosate and that’s the really frustrating situation we find ourselves in when we have resistance like this evolve.
The benefit of both paraquat and bromoxynil though, is that they tend to be better at controlling larger Russian-thistle later in hotter conditions. And so, when you’re dealing with Russian thistle in that sort of situation, you want to up your carrier volume and maybe carefully consider what kind of droplet size you would need to penetrate that Russian thistle canopy so you get really, really good coverage.
We found that to be a pretty good recipe for success. And it seems like all the farmers I talked to have their own little special recipe that they like to really hammer the Russian thistle with later in the season, just through hard-earned experience in those late summer months where it’s really hot, you got to come up with something that’s a little different than the normal glyphosate application.
There’s also, you know, growing adoption of these weed-sensing sprayer systems that does allow farmers to potentially put a lot more active ingredient per plant. But I always try and caution everyone when you have really dense populations of Russian thistle that you can radically exceed the total amount of active ingredient you’re allowed on that label per acre using one of those systems, if you mix up a really, really concentrated mix.
And so there is a balancing act, you do need to be aware of how much material you’re using per acre and make sure you stay in line with what the label says you’re allowed to do with those systems.
Drew Lyon: I think those systems also might allow you to use that higher carrier volume so that when you do spray a plant, you get it with a lot of carrier and hopefully get better coverage.
Dr. Ian Burke: And you can also use–the nozzles that come with those systems can be adjusted in a way that maybe you activate early and spray up one side and down the other side. These are digital systems. Plants are not digitally shaped. They’re not perfect little rectangles out there so you’re still using more than you would than if it could spray sort of perfectly shaped plant size. There’s still a lot of savings to be realized, you just got to be really careful about how you set that thing up and the concentrations of material you mix. But carrier volume can be adjusted very easily.
Drew Lyon: And that’s one of the issues with Russian thistle. You and I have worked with a former graduate student John Spring and Sam Revolinski, I believe. If you look at Russian thistles, they come in all different shapes and sizes. And I guess early on I was thinking maybe there’s different bio types, but they took a look and you understand the genetics better than I do, can you explain a little bit what their finding was?
Dr. Ian Burke: Yeah. So, it has what we call very low isolation by distance, which is a fancy term for saying that most of the Russian thistle that we encounter in the Pacific Northwest is very similar genetically. So, field to field, because of how it tumbles, and how every year there’s always some distribution of that plant by tumbling, and then it also can cross-pollinate, the overall genetic variation from plant to plant is very low. So, everyone’s dealing with essentially the same [plant]. Plant to plant variation is low, but it has a high level of genetic variation, right? So, it’s sort of a double-edged sword. It’s very well-suited–it has all the tools it needs to adapt to a new environment very easily and it doesn’t really matter where it comes from. When it does show up, it already has all those tools because populations that would roll into a new area have a significant proportion of the total genetic variation of the species.
Drew Lyon: Okay. So another reason why it’s so tough to deal with. Alright. Well, Russian thistle is the topic of the day. I think we can find another topic down the road. Seems like there’s always a weed to talk about, but this is one that’s been problematic this year and always is really in the low-rainfall area. So thanks for joining me today, Ian, and discussing a little bit about this troublesome weed Russian thistle.
Dr. Ian Burke: Thank you, Drew.
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 podcast app. If you have questions or topics you’d like to hear on future episodes, please email me at drew.lyon — that’s firstname.lastname@example.org — (email@example.com). You can find us online at smallgrains.wsu.edu and on Facebook and Twitter [X] @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.