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Talking Crop is a row crop production podcast that brings current trends, actionable management considerations, and research updates from guest experts to farmers, agribusiness representatives, and agriculture agency professionals.
Hello, and welcome to the Talking Crop Podcast. My name is Kathryn Seebruck, and I'm a commercial agriculture educator with University of Illinois Extension serving Jo Daviess, Stephenson, and Winnebago Counties. Talking Crop is a row crop production podcast with episodes occurring every other week during the growing season between the months of May and September. In each episode, I bring on a guest speaker to discuss topics related to their areas of expertise. In today's episode, I talk with Dr.
Kathryn:Marty Williams, who is an affiliate professor with the University of Illinois Department of Crop Sciences. Marty and I discuss his recent research on how weather conditions before, during, and after herbicide application can affect herbicide efficacy. We touched on what effect this has on herbicide resistance, and how integrated weed management can help offset some of these effects. In the episode description, I've linked Marty's website, which provides information about his lab as well as a list of his publications. And I've also provided links to the articles that we discussed in the episode. You'll find a link to the herbicide resistance database that is mentioned, along with my contact information and a link to the podcast survey. On the next episode of Talking Crop, I'll be speaking with Reagan Tibbs, a fellow commercial ag educator with Illinois Extension. That episode will be a little bit different from normal as we will be discussing some ag policy topics. And that episode will air on Wednesday, July 23. So now without further ado, please enjoy this episode of talking crop, how variable weather leads to varied herbicide efficacy with Dr. Marty Williams. Marty, welcome to the Talking Crop Podcast. I appreciate you taking the time to chat with me today.
Marty:Well, thanks, Kathryn. I appreciate the invitation and excited to talk about some of our research.
Kathryn:Starting with that right away, in the past five or so years, your lab has published a few different journal articles on, relatively the same topic, and that's essentially herbicide efficacy in varied or variable weather. And the number of these articles made me curious what brought this on? What was the impetus for this research getting started?
Marty:A couple of things got us interested in working on this. I should mention my colleague, Dr. Aaron Hager, the Extension Weed Specialist with the University of Illinois. He and I were visiting some years back about the amount of data generated by the herbicide evaluation program. This is a program that he leads up at Illinois that conducts about 100 trials each year on different herbicides, herbicide treatments, weed management tactics. He had been archiving that data. It was something that we decided, there's probably value. These individual trials serve a very specific purpose. Collectively, perhaps we can gain knowledge if we compiled across trials and framed questions that might be relevant to the industry, to growers. That's what we did. Early on, we thought this is great because one of the questions we had was how does weather affect herbicide performance? We know weather does and many things that affect herbicide performance. Weed species, perhaps their weed density, if soil active products soil texture, soil physical properties, a whole host of things, including herbicide rate. We really want to focus on weather because we've seen a pattern of more frequent weather extremes in recent decades. There's indication that this will continue into the future where we have less than ideal conditions for crop production. We had a bunch of data we want to do something useful with, and this is a great approach where instead most look at whether on herbicides has been say, two or three environments, maybe 10 environments at most to, to look at herbicide performance. Here's something where we could compile literally hundreds or thousands of trials to have up to thousands of environments to begin to look at tease apart. Just how does rainfall before or after herbicide application affect herbicide performance? Those types of questions where we couldn't do it if we were to start from scratch. By mining these historical databases, we're able to frame types of questions that are very relevant to the issues facing growers today.
Kathryn:You mentioned how there are a host of ways that the weather and the environment can affect herbicide efficacy. The biggest one, especially when if we start talking about post emergence herbicides specifically, the biggest one is of course rain fast periods. You want to make sure that you're not going to just wipe off the the herbicide straight from off the plant as soon as it's sprayed on, right? There are other effects that don't come top of mind. Can you talk about some of those?
Kathryn:Obviously, you guys did the research to determine, do these effects actually happen statistically, are they significant? But what in general are those other effects besides obviously rainfall after herbicide application at least for post emergence herbicides?
Marty:Sure. If you think about rainfall, temperature being likely drivers of some of the things that influence weed growth. And obviously, it influences crop growth as well. When we were looking at herbicide efficacy, how well do we control those weeds? You think about things that influence weed growth. Something with rainfall would influence just how much water might be in the soil profile for the plants to take up. Are these weeds under some type of drought stress condition? Because usually under drier conditions, you can have a thicker cuticle layer on the the leaves, which can reduce the amount of herbicide uptake through the leaf surface. Hotter conditions can actually increase, with adequate water, metabolism of certain herbicides. It can also increase weed growth where you might miss that window of opportunity to get the ideal weed growth stage to control the species.
Marty:Clearly, the same weather won't necessarily have the same effect on all weed species. There are certain species that are more adapted to drier, hotter conditions that might be more of a problem one year than another year. With a varying by species as well, there's a whole host of potential physiological mechanisms how weather influences weed growth and might impact how it interacts with the herbicide that's applied to it. There's a few out there that are pretty well known, and the benefit of this work is we're actually able to quantify more precisely how some rainfall pattern influence or air temperature pattern influences that product's performance on specific weed species.
Kathryn:Can you talk a little bit about what your research found? Like I said in the beginning, I know there were a few different papers. I'm thinking specifically right now about the most recent one on post emergence herbicide efficacy. What did you guys end up finding in your research after you compiled and analyzed all that data?
Marty:Well, let me backup just a moment here and walk through the approach that is compiling lots of trials over time and space. For all the post emergence work, we actually worked with a data set that we had compiled with Extension weed scientists from across The US. Not just the University of Illinois data set, but also herbicide evaluation programs at other land grant universities, from Texas to Ontario, Canada, from North Dakota to Virginia, about 20 institutions total, over 11,000 trials collectively, which represents over 10,000,000 observations of weeds in observations of weeds in experiments. Right? These are replicated experiments. Very powerful dataset. Then whittle that down to look at, just in this case, we tried to pick some of the herbicides and weeds that were most well represented. We're looking particularly at waterhemp, the morning glory species, and giant foxtail. Those were three species that were really represented well in this massive data set. Some of the most common post emergence herbicides, including, Fomesafen, Glyphosate, Mesotrione, and then a combination of Fomesafen plus Glyphosate. We also had another paper in there. We also looked at Glufosinate and used an analytical approach with these data to identify what are some of the major types of weather factors that influence performance. Rather than us saying, oh, we know it's rainfall, we're going to say how to rainfall. No.
Marty:We collected the environmental data for all of these thousands of trials whether it was rainfall or temperature, different time periods before application, during application, post application, amount of solar radiation, relative humidity, a whole host of different weather factors that help describe what happened in each trial. This analysis enables us to identify those weather factors that were most influential on how well the herbicide worked on each species. It varies by herbicide. Okay? For most of the post herbicides we looked at average temperature about ten days before herbicide application. About ten days after application were some of the biggest drivers, both temperature and precipitation were some of the big drivers. We talk about Glufosinate, then we also see how solar radiation the day of application can be important. What we found in general was that there's limits, I should say. We have these weather factors that are very important in how the herbicide performs. And as such, there are certain limits or these thresholds where herbicide efficacy can deteriorate and we lose the ability to successfully control that species.
Marty:And it often happened when we got to these more extreme types of events, extremely low rainfall or particularly high rainfall events. Same thing with temperature. If we had just in general, when we were in the when the average temperature was in the low 60s and cooler or in the upper 70s and warmer, many of these herbicide by weed species combinations, the weeds just were more likely to survive these applications. The more extreme types of rain those outlier kinds of events, it was really hard to have good control of the species is a general topic. There there was very specific, species herbicide combinations. They all didn't fit the same pattern. What I can say about is if we looked across all the species and all the types of herbicide treatments we looked at, it doesn't matter what the weather is. Somebody will succeed. Some somebody will breakthrough these individual herbicide treatments. If I can just add to that, the one thing we did see was that if we used combinations of post emergence herbicides, that reduced the risk of that incomplete control.
Marty:Didn't eliminate the risk, but in general, at least for the combinations of herbicides we looked at, there was more likely to be able to avoid a catastrophic failure in product performance.
Kathryn:I think that you talked about the methodology of putting this research together. In reading these papers, I thought it was really interesting and a great idea to take all of that data and it's interesting too because it's years and years of data too, right? It's just, like you said, a really robust data set to tell a really fascinating story across time to give us some really interesting insights and I know this is not really the scope of what we're talking about, but there's a paper that you did a while back as well on Glyphosate efficacy that you'd utilize the same data collection process for, which again told a really interesting story. It's very interesting research and when I was reading about it, I actually thought the opposite when it came to higher temperatures. I assumed that the herbicide would work better because the higher temperature would make the herbicide molecules work a little faster and all that but it was interesting to learn that.
Kathryn:No, it's actually the plant that works harder to overcome, potentially overcome that herbicide application. You guys can only really speculate about why these effects are happening with the weather and and the herbicide efficacy. Do you know if there's any research being done to look at those effects specifically to determine is it because the plant is increasing its metabolism in those higher temperatures, things of that nature?
Marty:Yeah. Good question, Kathryn, because when it comes down to it, the analytical approach we use, the type of data we have, what we're seeing are associations. We're not seeing the underlying mechanism by which each response occurs. We're unable to because, these are studies that have already happened. The data are what they are.
Marty:We can't go back and collect more data in any of these trials. The strength lies in the number of observations to see patterns that merit follow-up research, some of this mechanistic follow-up for research to see, Okay, exactly how are weeds surviving when we get to these more extreme types of weather events? Getting back to your question, is anyone following up with that? It's a wide open area for research. The challenge with picking a single variable, weather variable, and studying intensely is that you can look at a specific variable, but often it's multiple factors coming together that influence, how the plant responds. I think there's some great research to be done there. Probably the best research is if we could have combinations of, weather factors to test. It quickly becomes expensive and just a challenge as well. That's an area of research that's worth doing, probably an equally important area of research that might yield not only valuable science to the scientific community, but also valuable information to the crop production and production industry. How are we gonna use this information to do things differently? I feel like one common theme we see from our research is the challenge of relying on limited number of weed control tactics, whether it's how they perform in whatever weather might occur after planting. Also you alluded to the work we did previously or Glyphosate efficacy over time is that weeds are adapting. They're adapting to our management. That was really what we showed quite clearly with our research on Glyphosate that we're not really going to get into much today, but is how weed communities are adapting and not necessarily becoming like obvious like, oh, wow, now we have glyphosate resistance as how our, the scientific community measures glyphosate resistance. There adaptations going on that we can't even detect in, in our standard protocols. My hope is that this research it'd be great if it led to some looking at sort of the mechanistic of how plants, how weeds are responding. Also research on new tools to overcome, new tools, new weed management systems to overcome the variable weather that we're dealing with in the Midwest and also the adaptations. It's slow. Well, I shouldn't say slow on geological timescale. These rapid adaptations, to our management practices, those two things that are really a major outcome of this researcher and should be incentives to how are we going to overcome these challenges with weeds?
Marty:Because personally, I think weeds are with us for the long run. I'm optimistic that we have new tools coming out. It would be great if any of these new tools, we use them in a way that we prolong the longevity as well where the weeds don't just rapidly, within twenty years, adapt. Now that tool is no longer available, as is the case we've seen in large part with Glyphosate alone.
Kathryn:You touched on a couple of things that I was actually going to get to, which is great. The first being with these results, we're learning some things about how the weather affects herbicide efficacy and of course, it's very nuanced, right? There's different weed species, there's different herbicides that you use, and you did find maybe some generalizations. With those, do you have any recommendations to producers then in terms of maybe looking at the weather but that's the thing too. There's a big caveat there. We understandably cannot control the weather, and farmers are always under a time crunch when it comes to getting spraying done. They can try to take not just rainfall into account but temperatures before and after they're spraying but that gets very complicated very quickly, with all that said, do you still have any recommendations to producers in terms of taking this information and utilizing it in their operations?
Marty:Yes. I think that one of the key things is the more hurdles we can throw at the weed community, the better. That way we're not including some type of pre emergence applications from our the work that we did with post emergent herbicide applications. If you're relying on just post emergence products alone, it's a risky business. Having more tools included in there, such as a good pre emergence plan and not relying on that alone either because we've done the work with pre emergence herbicides, it's the same story. There are conditions that those products will not shine in for certain species, and particularly when we look at something season long. The more complicated we can make it for the weed community, the better. I know there's limits on what technology is available and what a grower can afford. There's a whole host of things growers are dealing with, all sorts of decisions and challenges they're faced with. There's going to be times where weeds are not the only thing they're working on, right? There's a lot of other considerations. I think, temper my comments with reality here, but there's a critical need for having a diverse amount of tactics as possible to reduce the chances for breakthroughs of species that are going to be problematic for years to come. The greater the diversity, I think growers should be thinking about. I don't think it's all in the growers either. There's a need for more tools, certainly chemistry, but also non chemical approaches as well. There is some innovation being done there with detection and robotics and physical weed control approaches.
Marty:Some of that innovation is making its way into the market in more specialty crop production and showing some success. In part, because they're in areas where you can control the amount of water out in California or other Western states where you control the water through irrigation, that's huge and that's not necessarily an option for everybody in the Midwest. There's some new technologies coming out, harvest weed seed control, another example. Again, we don't rely too heavily on that alone. Otherwise, we'll be selecting for species that set seed or shed seed before before harvest. But aiming for a combination, a system that has, as many opportunities to kill weeds or reduce seed production, the better.
Kathryn:Yeah, absolutely. I know that's the story that we always tell when it comes to herbicide resistance management. You want to throw as many tools at them as possible to make sure we are overcoming any potential, whether it be direct resistance or like you're talking about with that glyphosate paper just adaptations that they're throwing back at us. Want to be able to counter that with multiple methods of control which is really important and something we harp on a lot and it made me curious reading your papers about what these effects will have on herbicide resistance over time, the weather, it's currently variable.
Kathryn:It will likely become even more variable. We're due to have increased air temperatures over time that this research now can enhance or reduce herbicide efficacy depending on a lot of different factors and with that, I just wondered what your take on what the overall effect will have on herbicide resistance as a whole.
Marty:How we test herbicide resistance, how we confirm herbicide resistance is great. That's important. It captures the real obvious changes in weed populations that may be very obvious to the sex like suddenly my waterhemp is no longer controlled by Callisto type of thing. That's helpful. I think there's plenty of underreporting. There are those listeners who are aware of the website, Ian Heap's website on herbicide resistance globally. there's documentation there of species, populations, herbicides that have locations where resistance has just been confirmed. Just scratches the surface in my opinion. It's important.
Marty:It's great, but it does not completely account for all the resistance out as I mentioned earlier with our work with glyphosate, we saw in that work number of different seven different major agronomic weeds, many locations this deteriorating control with glyphosate over a twenty five year period we saw it time and again poor control more variable control over time and Kathryn for every single population at every location none of those were deemed glyphosate resistant, none of them met that criteria or had been flagged as screened for glyphosate resistance yet time and again across the board we saw this loss of control. These adaptations that might be a combination of small affects coming together with the location, perhaps with the weather, perhaps with population there and non target site types of mechanisms within the plant where collectively that product just doesn't work. Glyphosate alone just didn't work very well even though it didn't meet the criteria of glyphosate resistance. I think that's a real challenge with some of these metabolic based resistance mechanisms is that they can be these small effects coming together. When you throw in a few other aspects of the crop production, well, we didn't have the rainfall
Marty:we needed to have weeds growing well before application or whatever the combination would come together. I think that lends itself to opportunities of greater herbicide resistance and, whether we formally notice it and catalog it or not, is another issue, but on the ground, it's the same. It has huge implications to the grower. That this deteriorating, this loss of utility of some of the herbicides that we've relied on heavily for weed control. I hate to paint it as a gloom and doom here, but again, I get back to this underscores the need for having as diverse tactics as possible. The bottom line, I think that as thirty years ago, has it been that long? It has been that long with the introduction of, Roundup ready beans and then corn and cotton and other crops.
Marty:That period of simple weed management control, even simple approaches that look good initially those days are gone. Simplistic approach, we simply have to have more management involved and more decisions in being successful in our weed control programs than than we did a few decades ago. Yes. There's a lot to unpack with all of that. I think it's fascinating how there's so much nuance especially With that glyphosate paper. I'm glad you finally talked about it. We keep mentioning it. I'm glad you highlighted it a little bit. Drag it out. Yes.
Kathryn:A year or couple years ago, I was doing this presentation on herbicide resistance and I utilize that paper to talk about how it's not always explicit cases of true reported herbicide resistance that are causing these escapes and these issues but it's also those more indirect effects, I think is how I worded it. Especially based on what you talked about in that glyphosate paper. It's indirect effects of these adaptations that weeds are undergoing that the effect then looks, it looks like resistance but it's not true resistance. You talked about how it does sound like doom and gloom, but at the end of the day, the the best thing that we can do or that producers can do really is utilize an integrated weed management approach whereby they utilize more practices than just relying on herbicides. I also wanted to add that when I was thinking about the effects of weather on herbicide efficacy and how that can affect resistance.
Kathryn:I wondered if, maybe sometimes, you have those low levels of resistance and then, you have maybe a a weed escape not because of resistance and not because of a weed adaptation but now because of weather, how that can potentially then lead to quote unquote escapes and if they have low levels of resistance because they're not being controlled very well due to those weather conditions, then, you might end up with a resistance issue as a result and again, it wasn't directly because the the weed was exhibiting true resistance but it was because of that lack of proper control due to weather.
Marty:That enables, this is weather, these other factors that enable those alleles, those maybe small effect resistance type alleles to survive and be there for the next generation. And just the chance of building over time combinations of where you have weather enabling extreme weather or less than ideal weather enabling herbicide resistance to develop over time.
Kathryn:I know, like you said, of we're talking doom and gloom here but the the bright side of it is that at the end of the day, an integrated weed management approach is the best thing to do going forward because if the herbicide efficacy is being lowered due to resistance or a weed adaptation or the weather, you want to have something else in your back pocket to utilize. It's going to control them barring all those other factors. With all of this, I wondered then, is there potentially going to be an impact on corn and soybean yields due to this potential loss of herbicide efficacy with these varying weather conditions?
Marty:Excellent question, Kathryn. We've done some research on this. Actually using this large database, some of those trials had crop yield taken as well. Different herbicide treatments where you have we saw a range of different levels of weed control, early season, mid season, late season. We're in the process of continually adding to the database and running more analyses. If we look at some of the main drivers of yield loss in corn and soybean from these trials that are conducted we have thousands of trials, we find that when you have this less than ideal level of weed control it's not complete weed control. It's just a little better, say, on a scale of zero to 100, something like less than 95% control, early season, and then couple that with, say, challenging weather for the crop, particularly around flowering, whether it's corn silking, soybean flowering, those those challenging weather events exacerbate the, well, I should say, let me flip. Let me describe that differently. The low level the incomplete weed control exacerbates the effect of these challenging weather events on the crop.
Marty:We have some pretty significant yield losses. You have like 5% of the community out there that escapes and then you have either hot or dry conditions at the time this crop plant is very sensitive to stresses, which is often around flowering. We can have much greater yield losses than if we'd had perfect weed control. We've seen that both in corn and soybean, where it's obviously hard to have a completely weed free field. It takes a lot of work to achieve that. What we found is that if you have incomplete control and it doesn't have to be a disaster to still have pretty significant impact on the crop, particularly when the crop already has conditions that might stress it. It makes sense if you've got limited water supply and you have a few weeds out there using up soil water that the crop needs at flowering it makes biologically, it makes sense, but it is a little bit sobering. If we think about we're going to have, we're heading in a period where we're more likely to have warmer conditions, mid season, late season, and, and also we're likely to have drier conditions, mid season, late season in crop production warmer, drier, those were the types of conditions where having just a few weeds, really wreaks havoc on crop yield. We're not in the business of like, well, what's weed control going to be in, in 2040 or 2050? That's a big task. Ff we just think about the types of weather we're expected to have in the coming decades, it also argues and based on the work we've done these relationships with this more extreme weather on crop yield. If our weed management is not getting better there's a challenge there. I think it also speaks to the need for continuing. Well, I think continuing to invest in weed science research to come up with new tools, whether it's public sector, private sector, the need for new tools and fitting them in weed management systems that become, that are more resilient to extreme weather, I think is important. I think that's what that body of research on crop yield says is that if we look at what we're getting in the future, what likely to have in the future now is now we couldn't have a stronger need for more weed management tools being developed right now than ever.
Kathryn:Yes, 100%. We already talked a lot about the need for integrated weed management and to have more tools developed to put into our toolbox. The famous saying, I think that better off we're all going to be. That's definitely something to look forward to. Marty, thank you so much for joining me.
Kathryn:Again, I had a really great time speaking with you about this. As we talked in the beginning, my background is in weed science. I was especially excited to chat with you about this really interesting research. aAain, thank you so much for joining me. I appreciate it.
Marty:Thank you for the opportunity, Kathryn. It's been a pleasure.