S8 E11 - Enhanced Degradation of Triazine Herbicides

the University of Tennessee or any other associated group. And also, this is being taped right before an election. I just want to say that although I haven't given it yet, I still approve this message.

going to start doing the analysis. And I first started looking at Atrazine, and when I tried to measure the levels of Atrazine, there wasn't anything there. And that really puzzled me. So I thought, Well, maybe he didn't apply what he thought he applied. So then I went back through the samples, and I started with the first sample that I collected right after

application. And indeed, there was Atrazine there, but then I had collected over several, you know, every week for six weeks, and I started looking going forward, and after two weeks, there was no more accuracy. And I thought, well, maybe my analysis is wrong or something else. And so then I took the soils into the lab and did a lab study and found indeed, that the half life of Atrazine in the lab was about three days, and the

literature said it should be about 60 days. And so that's what started me in the whole thing, just trying to understand what happened, saw this enhanced degradation, and then looking at the literature, found out this wasn't a new phenomenon, and I worked with a weed scientist from USDA in Mississippi, Dr Krutz, and he had been working on it for a while, and then we just went from there.

Minnesota. Jerry Weber at North Carolina State. Terry laby at Arkansas, although John matice was a brilliant chemist and scientist, so really Matisse was or Matisse was actually the smart guy there. Morris Merkel at Texas A and M. David Shaw, Mississippi State. Bill banks at Georgia. Bill Witt at Kentucky. Jason Cruz, which Dale is already. Mentioned, and Dale Shaner At Colorado. Now currently, there are very few

groups working on herbicide fate in soils. I mean, Tim gray at Georgia, Travis Gannon in turf in North Carolina State, and me in Tennessee. And the reason for this is there's, you know, we could talk about another time, but I just have always been looking at it from an agronomic perspective. And so that's what we'll talk about, it. Why, when we get into why we looked at enhanced degradation was It was similar to what Dale was talking about, except that we were looking at just in general,

atrazine wasn't working like it was before. So that's how we got into the specific topic.

basically used on everything. And Atrazine is a triazine chemical. And I'm not even going to try to do anything chemically related to what explaining what a triazine is. All I'm going to say is that there are no naturally occurring triazines from an environmental perspective. I'm at least, I'm pretty sure that's true. And if, if that's not true, Dr Shaner can correct me on that. So before we go any further, let's discuss exactly what enhanced microbial degradation of

chemicals means. If I've got a new chemical and it's introduced into the soil environment, the microbes will eventually determine how to best metabolize or degrade that new molecule. So enhanced degradation is by no means unique to Atrazine, and many pesticides have had issues with rapid degradation after several years of use soil applied insecticides such as carbofuran, the carbamathyoate herbicides, which I don't think anybody uses anymore, they would have special adjuvants added to

them to discourage the enhanced microbial degradation. So that's that's what's happening. And so if you've got a completely novel type of chemistry now present in the soil environment, like a triazine, it has the chance to be more persistent to microbial degradation. So like Dr Shane was saying when it first came out, atrazine would last a long time, 60 days, 70 days, easy. But now with the enhanced degradation, it just doesn't

last as long. Does that kind of introduce the topic of what we're talking about?

soils that have had multiple applications of Atrazine. And as he said, you know, atrazine was introduced in the 50s, and so it's been used now for about 70 years. And it's not too surprising that soils will will our bacteria in the soil will evolve to start using this new source of energy. And in the case of the triazines, one of the main reasons they're using it is for a nitrogen source, because if you have high

nitrogen, it will inhibit the degradation of Atrazine. So adapted and non adaptive just really means, what's the history of the soil? Has it seen these herbicides before? If it has, then you will likely find these microorganisms that will degrade it.

just the opposite. With adapted soils, in adapted soils, they degrade the herbicide more rapidly when the PHS are greater than about 5.4 where in non adapted soils, it's just the opposite. They degrade faster in pH soils less than five or less than six, and the reason is in the non adapted soils, the primary path of degradation is through chemical hydrolysis, where at and the reason that and the acidic conditions of a debt or non adapted soils enhance or enhance that Chemical

degradation. Whereas in non adapted so, or in adapted soils at low pH, the herbicide binds more readily to the soil, and that makes it unavailable to the microorganisms. So when you get into basic soils, the herbicides more available, more bioavailable. Organisms get to it more readily and they degrade

it more rapidly. We have a paper. Well, Jason has a paper on this whole thing, on the effect of moisture and temperature, etc. And as you would expect, under very dry conditions, it's all dependent on how active the microorganisms are so in dry conditions, the microorganisms are depressed, and so you'll have longer carryover or more less rates of degradation. Would you agree with that Tom?

try to expound on that little bit? Are you good to go Dale?

time. It just seemed like the Atrazine was not working as well, so I conducted a research project to determine how widespread Atrazine enhanced degradation was. And if we got

time, I'm just going to read all the cooperators that I had. And the reason I'm doing this is to show you when we're talking about the breadth of the PHS and the soil textures and everything, I just so we had Larry Steckel out of Tennessee, Sharon clay, South Dakota State, Mike Owen, Iowa State, Bill Kern Penn State, Randall curry, Kansas State, Bob Scott, Arkansas, Christie Sprague, Michigan State, Dan Stevenson and Donnie Miller. Louisiana State, Eric prosco, Georgia,

James gricker, Texas, A and M Jim Martin, Kentucky. Jason crooks was done on study. Mississippi State. Kevin Bradley at Missouri. Mark Bernards in Western Illinois. Peter Daltrey, Texas, tech, Stephen knevik in Nebraska. Vince Davis, Wisconsin. Bob Klein Nebraska. And then I had, I had studies in

there too. So I understand that took a little time to read all those names and everything, but I just wanted to share how widespread our samples were from the United States, and so we when it comes to textures and PHS and all that, we had a really strong data set. In fact, there were, and what we did was to use your terminology, adapted and non adapted. We call them

history and no history soils. But each cooperator would get a history soil which was easy to find, and then they would find as close to possible, a non history soil, which was sometimes difficult to find. And we defined history as five years or more, and Dale's alluded to that, but and realizing that some of these fields have decades of atrazine use, I mean,

not five years. So that's how we did the study we did, and then we took those soils, and we're really sampling the microbial population in the soils, to be honest with you, that's really what we're sampling. And then we did a lab assay. We fortified all those soils with a known amount of Atrazine, let them degrade and run the standard curves on on all that. So it was a massive study. We had 60 different comparisons, and it was like one. 1856, samples, and so it's a really strong data

set. So the take home message is, what's the effects of texture? There's no effective texture. What is the effective pH? There's no effective pH because the enhancement is so pronounced, you always have enhancement, or you always have rapid degradation. So either way, you're not having any actually persistence. So that's kind of like, you know, and we're not, we're not, I'm not in all saying that if you're completely dry immediately after application, you're not going to

have slower degradation because there's no microbial growth. Dr Shaner is exactly correct on that.

of the Atrazine use. Okay, that's so and because a lot of these are not taken by the fact that their staff, their farmers, their consultants, I mean, it's it was, I was really proud of the data set that we had. And really, if you've got that paper ahead of you, if you look at figure one on the paper, which I think was the most salient figure, it basically shows everywhere. The half lives are always either short or the enhancement is very pronounced. Okay, that's kind of when I when

I kind of looked at the data. I'm not sure. I'm probably not. I'm not speaking to your question, Sarah, so you want to re ask it again, I don't think I answered your question.

years? Conversely, if I have a long rotation, let's say I rotate away from corn, does that microbial community revert back and kind of lose that ability for enhanced degradation?

10 applications. Okay, so that's that's kind of cheating. The other thing is, although I have no data on this statement, I'm going to say it with great confidence, once you have the enhancement, it's there forever, because there's no fitness penalty that would favor other organisms that would not have the enhancement. And there is a tremendous amount of literature in the microbial community, not the microbial community, the scientific community about Atrazine degradation and what

genes do this. And they've really spent a lot of effort on there, because the government spent a lot of money figuring all this out. And so I don't think the enhancement you can you cannot undo the enhancement. I don't think. And that is paralleled by the agronomic observations that even if you stay out of corn for five years and you come back the atrazine still doesn't work very well. So that's, that's, that's my observation on that. Dale, what do you think Dale?

beginning. I took samples at the beginning of the year, and then through the year, and in one case where they had not applied Atrazine for about five years, and when I first took a sample of that soil, the rate of degradation was fairly slow, but within two weeks, it had gotten back to what had been before. So it just took a little while for that Atrazine enhancement to go

on. And I remember one paper I read, I think it came out of Europe, where they concluded that the genes, the bacterial genes that degrade Atrazine, it's about four genes that are all together are actually on a plasmid, and that the microorganisms will if they don't see Atrazine, they will shed that plasmid, but it's still in the soil, and as soon as Atrazine appears, they will take that plasmid back up and

start using it again. So it's like it's just what Tom said, once you have Atrazine degradation, you'll probably have it forever. I had one soil in eastern Colorado where they had gone organic about 30 years before. They had used Atrazine prior to that, but they had been gone organic for 30 years, so they had not used any Atrazine, and in those soils, I did not find enhanced degradation, but that's a pretty long time for

farmers stay out of it. So I agree with what Tom saying is that once you have it, you might as well assume you're always going to have it. You might slow it down a little bit, but it's really probably not going to make much of an effect.

I think the label needs to be drastically changed, because they have limits on how much atrazine can be applied, and they have limits on follow crops. I got a call once from a farmers down in Texas. They had applied Atrazine the year before they wanted to plant followed up with a sensitive follow crop. They wanted to know if they needed to worry, and so I had them send me soils. There was no Atrazine in the soils that had

enhanced degradation. And I told them, Well, I'm not going to tell you to go against the label, but there's no Atrazine in the soil, so I wouldn't worry about it. And so that's, that's what's going to happen. The more harder to control weeds like prickly sida, Morningglory, etc. You can't depend on Atrazine to control it, because it's just not going to stay a lot round long enough. So for farmers trying to use Atrazine, they

just have to know that this is a short residual herbicide. You may get two or three weeks max weed control, and then it's going to be gone and or sooner than that, and so you need to start mixing it with other herbicides. And it also applies to other triazine symmetrical triazines, the proposes the simazines, those also show rapid degradation. Metribuzin, interestingly, does not, at least not in my hands. Maybe Tom has got different experiences. Experience. Hexazazone does not

because they're asymmetrical. They're they're not symmetrical triazine, so they're not degraded in the same way. So that's, you know, I think for farmers, you just have to tell them, Don't depend on Atrazine to give you the weed control you used to think you're used to what?

registrants do it on soils with no previous Atrazine use. So they are dictating to the registrant, when they do a study, to pick a soil that's completely different from where it's almost always being used in the real United States use scenario. The other thing is, atrazine has post activity, so it's used as a synergist to the HPPD inhibiting herbicides. It's unchanged by the Atrazine soil behavior. Everybody. It doesn't

matter if it's degraded or not. Also, as Dale said, delaying the Atrazine application of soil as long as possible, which is what's happening with some of the like helix GT and all those things. For example, an early post treatment would move the Atrazine residual later in the season to provide more, longer lasting control. So that would be another aspect to it. And the crop safety of Atrazine post is fine. I mean, unless you get a lot, but yeah, and I don't, and I don't think there's any way

there. I mean, I agree agronomically with what Dale fan say is saying about raising the rates, but Atrazine is one of those things that's under under duress because of the environmental loadings and so forth. So I don't, although agronomically, that'd be true, that's not going to happen. I

different cropping situations. And if you're in any kind of situation has corn in it, atrazine really doesn't leach because it just degrades too rapidly, whereas if you look at it under a non adapted soil, you can show quite a bit of leaching with it. So again, the models are wrong. The EPA needs to be educated that this Atrazine degradation, enhanced Atrazine degradation, is a factor across not just the US, but across the whole world. And when they're labeling it. It's really not the

same herbicide that they are used to. And like Tom said, I would, I would really push post early post applications or whatever will give you the longest residual of Atrazine and use something else Pre.

field before it's associated with the soil microbes. And this often happens, you spray the herbicide on the soil, you get a torrential rainfall, and if there's any off target movement in that surface overland flow, then it doesn't really matter how quickly the Atrazine is degraded, because it never gets to the soil to start with. Therefore, from one perspective, the surface water loadings are not largely affected by the

Atrazine enhanced degradation. The surface water loadings may not be I agree completely with Dale Shaner about the subsurface of the leaching. It doesn't get anywhere because it's degraded in a matter of days. And all the models and I, you know, would do modeling work, not as good as Jason Cruz, by the way, but they always overestimate leaching by a factor of 1000 or something.

And it's mind boggling how wrong the models are. So that's kind of my thoughts on the surface load, because the reality is in there's parts of Iowa the Atrazine is getting into the rivers. I mean, they measure it. The USGS does a finance a very good job of finding Atrazine, quantifying in the barbers. So it's getting there, even though the enhancement of degradation, I would make the case, is actually ubiquitous all throughout Iowa, in those watersheds. But it just it

doesn't affect the enhanced degradation. Doesn't affect it because it doesn't get to the soil, it washes off before it gets into the ability of the soil to degrade it. So that's one way of looking at it

tell farmers that? That's a good question. I would one look at the history of triazine use, and how is this is the pattern of weeds in the field uniform, or does it occur in spots? Because that's one of the first signs that you're getting resistance. Is that the first sign of resistance is that weeds will occur in at least initially. Will we occur in clumps? Whereas if you had enhanced degradation, it would probably be over the whole field, uniformly sent over the whole field. So that would

be one thing I would look for. Tom probably has, he has fairly more experience than that. But that's what I would do, is, how do you tell them? Well, one, let them know that this happens. Ask them, Is it, are there other weeds in that field that are not being controlled? And if there are, then it's probably not resistance, because with resistance, it's usually only one species. You don't get it across multiple species, at least all at the same time. And so I would look at the pattern

of pattern of weeds. I would look at our other weeds being controlled. Is it a weed that you've always had problems controlling with Atrazine, like the morningglories, the prickly sida is some of the other weeds. Are they being? Were they controlled in the past, and not now? But again? What's the pattern of the weeds in the field? What do you think Tom?

this thing called Walking fields. I mean, I know that's kind of like never going to happen again, but so you've put down a pre cultivate corn once, and you're done. Okay. So it's just not that way. Now, with the size of farms, there's no cultivation at all. There's no mechanical control at all. So that's a very big change from historical perspectives. And everybody's coming back with a post and so and you know, 25 years ago, the post cleaned everything up perfectly, and now

that's just not the way it is anymore. But I would, I would just echo what Dale saying on that. But I think the farmers, if they're going corn or sugar cane or grain circle, they understand the Atrazine isn't what it was several decades ago.

it's probably not a practical solution. I did a study with another person, USDA, looking at bio barriers, where they where they were, looking at trying to enhance, try nitrogen, leaching around uh catalogs, and we looked at the effect of that with Atrazine. And indeed, in those conditions, we could show that Atrazine degradation was was slow, but again, that was under laboratory conditions. We're trying to give a farmer

recommendation to enhance to increase their nitrogen. I think the pollution from nitrogen is way higher than trying to enhance the persistence of Atrazine.

the enhanced degradation. At least it has them until now that I know of hexazinone is one that this enhanced degradation doesn't happen. But working again with this person who was doing bio barriers, we took hexazinone and used soils from an alfalfa field that had been treated with it, and we were able actually to induce the enhanced degradation in about six weeks. So every herbicide has the potential of developing

or, you know, selecting for the right microorganisms. But any selection pressure on the environment, you're going to start selecting for things. You give the microorganisms a new energy source, they're going to work hard to take, you know, take advantage of it, and so using rotations of herbicides doing everything we talk about integrative management, that's the that's going to be the key. Don't depend on any one herbicide, whether it's resistance, enhanced degradation

or whatever, to to manage your weeds. That would be my my story to the farmers, or my recommendation. What do you think? Tom,

have to do, it just makes life more complicated. And so in answer to your question, if I was a young researcher, I mean, I'm 100 years older than I am now, I would spend my time in mechanical weed control, robots, drones, whatever that can kill weeds without chemicals. And this is because sooner or later, the regulators will try to make chemicals not available. And this is already happening in Europe, but the governments are

regulating the farmers out of business. And so I would, I would visit, you know, when I go travel, and they'll say, Well, how do you do such and such? We can't use paraquat. We can't use that chemical. We can't use, I mean, atrazine, I'm not sure. I think it's banned in Europe. And there's, there's not a lot of maize in Europe anyway, it's not a huge crop like it is here. So, I mean, yeah, I think there's chemicals in many of the public

is bad. Chemicals are bad, and the reason they're so extremely widely used is because they're so unbelievably effective. It's like, whenever I have an infection in my arm, I don't sit there and say, I'm going to be holistic and not and not put anything on it. No, I'm going to put some an antibiotic on it immediately. You know, I'm going to treat it immediately. And that's the same thing. So, and it's going to be challenging, and because I think we all understand the regulatory

hurdles are only getting more exacerbated. So that's a whole nother. That's a whole nother podcast. So, but yeah, that's kind of my thoughts on it. The golden days of weed control were really nice for the farmers, and those are gone.

control. They still have to control the weeds and the use of robotics, some of the newer technologies, they're all going to have their weaknesses, they're all going to have their strengths. But there is no silver bullet. People thought it was with Roundup Ready, and it it was a good ride for 10-15, years. But, you know, it broke. Everything's going to break if

you depend on it entirely. So integrated weed control, using his new technology that we can you know, it's some ways I'm kind of sad I've retired from Weed Science, because I think there's a lot of exciting areas to work in out there and and I hope the young scientists Take advantage of that. Tom?

dollars on it. And if they had not developed Roundup Ready corn, and if they had not completely squelched the Liberty Link soybean seed trade, and that's clearly an antitrust issue, but not going to say anything else on that, because I'm not going to get sued, then the glyphosate resistance issues we now have would be much less and could possibly have been largely avoided, at least, if you agree with Stephen Powell, who is a real brilliant researcher out of Australia, and

he had this double knock theory where if you have two modes of action, you go back and forth, back and forth, you can you'll go 20, 30,40, years. So yeah, we had a silver bullet, and we had the golden age, but no longer. And by the way, it was great for the farmers while it lasted. So I'm happy for the farmers, but we're not there anymore, and those are historical lessons we can learn and go forward from there. So just a thought, few thoughts.

it. And if somebody wanted a good background on enhanced degradation, I would recommend that particular paper.

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