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Arkansas Turfgrass Association – ResistPOA Series: Shawn Askew & Clebson Goncalves
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Arkansas Turgrass – Julie Holt, Content Director, TheTurfZone.com
TheTurfZone: Welcome to TheTurfZone. In this episode, we continue our series on the USDA-funded ResistPoa Project. In this episode we’re talking Shawn Askew, Professor at Virginia Tech, and Clebson Goncalves, post-doctoral associate at Virginia Tech. Welcome, Shawn and Clebson.
Shawn Askew: Thanks for having us.
TTZ: Thanks for joining us. So let’s get right into the ResistPoa Project and your part of it. Most turfgrass scientists have had, for lack of a better word, a professional relationship with annual bluegrass for their entire career, what’s your background and history with poa?
SA: Like you said, as with most turf specialists that do work on weeds, within the first week on the job, I was handling questions related to poa annua, and it’s just so pervasive in the industry. It’s just one of those things and not just if you look at it across the country or regions, whatever. It’s everywhere – it’s global, but temporally, looking back in time. Poa has been a problem in the United States for as long as we have managed turf. I’ve found publications back in the 1920s where poa was a routine, it was as common then as it is today as a weed of turfgrass. If you thing about the characteristics that we would apply to it today, the exact same characteristics were applied back then. They called it “poa” in short. So it was already so old of a problem that they had a shortened name based on the genus in 1921. They observed the seasonal fluctuation in population levels, the seed production, the aesthetics, how it decreses aesthetics, was all commonplace. So this beast has been with us for quite some time and it’s probably not going to soon go away.
TTZ: With that long history and knowing that it has been a challenge and has been present for so long, what is the hope with the ResistPoa Project, what new knowledge or what new management techniques are we hoping to gain from this project?
SA: When you look back at what has been done, prior to the ResistPoa Project, it’s mostly chemical herbicides, predominantly synthetic chemical herbicides and those are the strategies that have been evaluated for so many years and that largely have failed for so many years. We have some solutions on the market, but for poa annua, they are often difficult to implement, complicated requirements, need a temperature zone that you have to be in or you get too much turf injury, so for the longest time it’s been difficult to find a true selective herbicide for this weed. Now that may be changing, this is off topic, that may be changing with this new herbicide, methiozolin, PoaCure, which actually is not part of the ResistPoa Project, but ResistPoa was born out of the challenges that we have experienced with conventional herbicides. So what it’s going to do is expand our knowledge a little bit better on those aspects of poa annua control that are now solely dependent on which synthetic herbicide to spray today or tomorrow or next week. We’re looking more at the biology of the weed and trying to exploit its weaknesses. We’re looking at how different types of turf would be more or less competitive with annual bluegrass and we’re also, to speak to the synthetic herbicide issues that we often see, we’re looking at the widespread resistance of poa annua to the various herbicides that we do have. So we have limited options in turf for annual bluegrass control because of the similar physiology between the weed and the turf, but even the few options we have, poa annua develops resistance to them very rapidly. In fact, this weed, annual bluegrass, is one of the most adaptive plants on the planet. It’s one of the only higher plants that can survive in Antarctica. It also is one of the most highly-ranked plants on the herbicide database, the weed science database that we have for herbicide resistance. So poa annua has developed resistance to pretty much every herbicide that’s ever been thrown at it throughout history if there’s ever been any amount of time for the plant to be exposed to the herbicide. And in some cases poa annua has developed resistance—one plant, one individual can develop resistance to as many as six or more different herbicide modes of action. So we’re going to try to better characterize—some of these things are known in situations like wheat production or other agricultural settings. We’re going to try to get a better idea of exactly how widespread and pervasive the resistance issue is in turf and what are the major players involved with resistance. Which herbicides are developing resistance to more populations nationwide compared to others, and how do we deal with that both from an educational standpoint as well as from a practical management or applied standpoint.
TTZ: And how would rate annual bluegrass, how does it rank in the list of weeds there in Virginia?
SA: It’s among the top three most common weeds that we would encounter in turf systems and I would say arguably also among the top three most troublesome. Now the degree of how troublesome annual bluegrass is going to be is situation dependent. Some sites, as long as we don’t have herbicide resistance in warm season turf, if you can go out with glyphosate during dormancy of the turf and control annual bluegrass, that’s not that difficult, right? There can be some situations with warming spells in the winter and early green-up that can lead to turf injury, so yes it can be difficult, but for the most part it’s pretty easy to control poa annua with Roundup. Likewise, the acetolactate-synthase inhibiting herbicides like sulfonylureas and imidazolinone, there’s a number of those marketed for warm season turf and they control poa annua very well as long as the weed has not developed resistance to them. The biggest challenge we would have in Virginia utilizing some of these options is that we’re on the northern extreme of warm season growing weather and therefore most of our turf facilities are going to incorporate both cool season and warm season grasses. The cool season grasses are extremely sensitive to any level of drift or tracking or runoff from that class of chemistry, the acetolactate synthase inhibitors. So that’s one of our challenges is trying to keep the stuff we want to kill poa off the stuff that we don’t want to die as collateral damage. But yes, it’s definitely a challenge across all of our systems, whether it’s in cool season turf or warm season turf and in Virginia we deal with both of those issues, because we have a transitional climate.
TTZ: So getting back to the ResistPoa Project, tell me about the specific objectives that you’re pursuing as part of the project, and how does that partner with what you’re doing outside of the project?
SA: First let me say that Clebson is the technical arm of our project. He came on board with my lab in October as a post-doctoral associate. So Clebson is pretty much manning our ResistPoa Project in Virginia now ever since he started. He’s doing an outstanding job, I might add. The projects that we are responsible for include five different components and so we’re dealing with – the largest project within ResistPoa has to do with assessing how widespread herbicide resistance is with this weed. And so to do that, nationwide all the different universities are collecting approximately 2000 populations of poa annua as equally split as possible as we can do between golf, athletic sports, home lawns and sod production. So all of these 2000 populations are being screened against at least 10 different herbicide modes of action. We’re trying to determine how widespread herbicide resistance cases are and for what herbicides. So my lab is co-lead with Texas A&M on that particular part of the project, but I think every participant in the grant project are contributing to that particular objective. We are also co-lead on a related objective to that, so Phase II of the pre-screening project can take several different directions. Scott McElroy at Auburn is looking at target site resistance. Travis Gannon and others are looking at non-target site resistance mechanisms. And then myself and Matt Elmore from Rutgers and I thought was Bert McCarty at Clemson, Clebson says it might be Jay McCurdy at Mississippi State, but I know it’s one other, there’s three universities that are going to phenotype resistance cases by mode of action. So Virginia Tech is responsible for four different modes of action, or types of herbicides that we’re responsible for screening at what rate do these various populations stop responding to the herbicide. So we basically, I keep saying phenotype them to the resistance case. So phenotype is just a description of some characteristic of a plant and this case the characteristic is the resistance factor just indicates, compared to a susceptible population, if you had a resistance factor of four, then that means the population we’re talking about, it takes four times more herbicide to control that population than a susceptible population, so that’s the second part. So those two combined, and I think Clebson would agree, are the biggest workload. We’re responsible for screening 200 populations from Virginia, West Virginia, and Southern Maryland. And we’re responsible for doing rate response testing on, we don’t know at this point, but probably as many as 100 populations coming from across the country that people are going to be sending to us.
So the third project that we’re looking at has to do with developing a hydrothermal model for poa annua seedling emergence. We’re monitoring, continuously, the soil moisture and temperature at two different sites – one is in Richmond, Virgina, and the other here in Blacksburg – and every two weeks, we’re assessing the number of poa annua plants that have emerged in the plots. Those are carefully removed without disturbing the plot, so that’s going to go on for two years, this monitoring. What we’re hoping to do is to use data from multiple sites like our two sites, coming nationwide, to develop a model that can predict when poa annua will emerge and when it is unlikely to be emerging and that would help with various types of treatment input such as pre emergence herbicides and the like.
So that’s three, the fourth project that we’re working on has to do with determining which types of turf will best suppress annual bluegrass. So for example, if you had the option of growing tall fescue compared to Kentucky Bluegrass, which one is going to suppress poa better? Simple things like that, having good data to make management decisions, that’s just one little piece of the puzzle, but to manage poa successfully is going to require numerous pieces. Herbicides or those types of treatments are just one small component of a successful program. You have to look at your fertility program, you have to look at compaction alleviation. All the agronomic inputs in turf. Poa’s just not an easy weed to control.
Then we have one final objective that we are working on that that has to do with evaluating alternatives to synthetic herbicides for control of poa, and most of the work that’s being done nationwide on this has to do with utilizing organic products such as vinegar or associated chemical products that are registered or certified organic. One of the things that we’ve done that kind of deviates from the rest of the SCRI team, the ResistPoa team is that we designed some studies on our own that look at treatments that are more mechanical in nature to control poa, because in the past I have seen these to be more effective than some of the chemical organic options. These would include things like shading, solarization, which is using plastic to create an abnormally heated soil condition and we’re talking hot enough to actually kill weed seed. We’re also using direct flaming, using a propane torch and that’s some interesting work, and boiling water. Things like that where we’re actually causing direct physical damage to poa. Ironically, something as odd as direct flaming on turf, we’re getting selectivity and it’s not the type of selectivity you might expect. Yes, when you go over the turf with a propane torch, what you’re left with immediately afterward is a black, charred landscape. There is nothing green remaining. But the reason I said ironically — you can come back literally a week and a half later and in some of our plots we’re seeing 75% recovery of the turf and poa annua is gone. And so Clebson has since expanded that work on flame weed control in turf far beyond our original intent just to look at poa and we’re finding some very interesting results from that.
TTZ: So it sounds like you have a full plate in relation to this project, for sure.
SA: It’s a lot of work, but it’s a lot of opportunity to make some good discoveries along with our colleagues nationwide.
TTZ: So in terms of our listeners and readers of the magazines that will also have a print version and some resources that accompany this podcast series, there are some existing cultural practices and management strategies that they’re using now. But is there anything thus far, around the halfway point for you guys, the funded portion of this project, is there any data thus far that turfgrass manager can add to their toolbelt and help with management right now?
SA: I would say that from that standpoint, from what can I apply immediately standpoint, I would say the best thing that has come out of this project is the extension, website and related extension materials that Jay McCurdy has produced. He’s the lead on the extension side, basically his job from that standpoint is to compile the information that’s being generated from this massive project and make it end-user available, so that ResistPoa website in my opinion is the best thing that’s come out of this.
As to direct data that an end user can use, I would say, no. I personally am not at a position right now to alter my recommendations based on results from the studies because even though we’re about halfway through, we haven’t really gotten into the statistical analysis stage for much of the work that’s been done, so trying to draw inferences from the work is a bit limited. I always joke to people that I like to see things about eight times before I’m willing to recommend it, but I will say that I can see that we are moving in directions, just like for example the flame weed control that I just mentioned, that was from my perspective, totally unexpected. I never would’ve thought that I would be doing something that at least sounds so silly as to go out into open turf and just burn it all down as if you’re going to get selective weed control. So I was amazed at what Clebson has produced with those experiments and how rapidly the turf can recover. Which makes sense because open prairies throughout history are going to be exposed to fire and those plants have evolved to be adapted to rapidly recover from fire and not all plants can do that. So you’re going to gain some natural selectivity.
The problem is, and I don’t want to spend too much time on this topic, but the problem is that it’s all dependent upon what weed species you happen to have on your site. If they tend to be susceptible to fire you’re going to do a great job with it. There are some types of weeds that we really don’t want to have in our turf that are quite tolerant of fire, so that’d be one limitation. In terms of direct applied effects, we haven’t even started applying modeling techniques to our hydrothermal data, we’re not done with the nationwide resistance screen, so we’re kind of we’re right in the middle of everything and we really haven’t started to draw any inferences because we haven’t compiled all the data. That’s the problem with these things – so much work. I can’t tell you how many thousands of man hours have already been devoted to this and right now, if you wanted something tangible, it’s really hard for me to point to that. But, believe me, we’re heading in that direction, having been immersed in it for a couple of years I can tell you we’re definitely going to have some meaningful publications, some meaningful discoveries that I think will improve our understanding of poa and therefore our ability to kill it.
TTZ: Ok, Shawn, let’s close out with this – what’s something unexpected or a new challenge you’ve discovered as result of this research?
SA: I would say that this research has really shown, or reiterated for me just how variable poa annua is as a plant. We’ve seen some really bizarre things in the research. So Clebson now has about 100 populations that we’ve screened from our region. For example, we’ve had a couple of populations—3 to 5 – so out of a hundred populations, that’s five percent. So check this out, these plants are mature poa annua plants managed in the greenhouse. Upon maturity of course they produce a flowering stalk, bloom and they start to produce seed on that seedhead. And then guess what? The seed germinate, in midair, on the seedhead. They grow to a fully mature poa annua plant while still attached to the original seedhead and each of those plants start to produce seedhead, while still dangling from the original plant. They call that vivipary, it’s something that is not rare, well I guess it is rare, but it’s not unheard of in the plant communities, but for poa annua to be able to do that, it’s just something that you often see associated with tropical plants. And also for five percent of our populations to be doing that and the others not, is just bizarre. And it speaks to how highly adaptive this plant is. I tweeted this information out and showed some pictures of these plants that were exhibiting the vivipary
and Fred Yelverton at North Carolina State chimed in on that discussion and said that he had seen the same thing in an in-play golf course. So they were having some really weird phenotypic expressions from poa, went out to look at it and the plants were doing the same thing – producing mature seed-bearing plants on the seedhead of another plant.
Another thing that we’ve noted and that has become quite a challenge for us that’s related to the variability among populations, is that there are several of our populations despite Clebson’s best efforts, which are pretty good efforts, he’s gotten excellent seed production from most of our populations – we’ve got some populations we cannot get to make a seedhead. So there’s a high degree of variability. You’ve got populations right here that came from a particular region, maybe Richmond, Virginia, producing seedheads left and right, we’re bagging them, we’re getting plenty of seed to do subsequent research. Another population that also perhaps came from Richmond, from a different setting, we cannot stimulate those plants to produce a seed. So the problem with poa annua, I think throughout history, is its variability and how highly adaptive the plant is. That’s not going to go away and unfortunately for our objective on the ResistPoa team, it’s going to make it very difficult for us to come out of this with a clear, concise message to the end-user and say, “Oh, poa annua? Do this.” Because it’s going to always depend on local environmental conditions and it’s going to depend on the genetics in that population. Poa has diversified itself for a reason. When plants evolve that level of genetic diversity, such that they can adapt to pretty much any environment that the globe has to offer, then they’re going to respond, one population versus another, differently to our treatment programs. I guess suffice it to say, poa’s always going to be difficult to control. That’s one thing that we already knew, but we’re just strengthening that standpoint with the data that we’re collecting.
TTZ: It sounds like you definitely have your work cut out for you for the remainder of this project—and potentially beyond that.
SA: Yes, Clebson does have his work cut out for him.
TTZ: Shawn and Clebson, thank you so much for taking time to talk today.
SA: Thank you for having us.
TTZ: For resources and link associated with this podcast, check out our show notes. And don’t miss an episode, subscribe at Apple podcasts, Spotify or wherever you get your podcasts. You can also visit us at TheTurfZone.com.
For more information, visit resistpoa.org and follow @ResistPoa on Twitter.
