Weather and weed control: past, present, and future

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Jodi:

Welcome to the Successful Farming podcast. I'm Jodi Henke. This podcast is brought to you by the Enlist Weed Control System. Visit enlist.com to learn more about no nonsense weed control. From flooded spring fields to summer hail storms and drought, farmers are well aware the weather's changing. It often means spring planting can't happen on time or has to be done twice to make up for catastrophic losses of young seedlings. According to a joint study between the University of Illinois and the USDA ARS, it also means common pre-emergence herbicides are less effective. With less weed control at the beginning of the season, farmers are forced to rely more heavily on post-emergent herbicides or risk yield loss. DeAnna Thomas is visiting with Dr. Aaron Hager, a weed scientist, associate professor and faculty extension specialist at the University of Illinois. He is also a part of this research team.

DeAnna:

It's so great to visit with you. And here it is, it's 2021, the calendar is about to strike April. And I say strike April because farmers are anxiously awaiting that date when they can get into the field. And I know, I'm sure you've gotten phone calls as farmers really get ready to gear up for planting season.

Aaron:

It's that time of year. And it's a great time of year, the days are getting longer, the sun's coming up earlier in the morning and setting later in the evening and the fields are starting to green up. Not only green, but in some instances some of our winter annuals are getting fairly close to flowering. And so purple landscape is going to be with us here very soon. Some of the yellow flowered winter annual species will begin showing their brilliant colors. So I always kind of think of this time of year is when we have a bit of splash, a color splash on a somewhat otherwise mundane Illinois landscape.

DeAnna:

Everyone always likes those purple and yellow flowers.

Aaron:

Oh, they are pretty. They do attract a lot of attention.

DeAnna:

As you have worked through COVID, you've been working on research and partnering with folks at USDA, and I can't wait to dig into this with you, but when we look at the last five years of agriculture, production agriculture in particular, mother nature, plummeting markets, it's not been the most enjoyable experience to be a farmer.

Aaron:

I would say a bit of a challenge would be a bit of an understatement. Talking with some of the local farmers around close to where we live, there's a lot of issues, obviously, that they are quite concerned about. Some things are in their control, in their grasp of control, but obviously, no big surprise, there's a lot of issues that have a direct effect on the farmers in the field that may be a bit beyond what their actual control. Markets, for example. What's going to be the marketable price of the 2021 crop? When it comes out of the field, a bit beyond our control, obviously, and sometimes a little bit hard to predict what it's going to be.

DeAnna:

One of the things that I really like about the research that you've done recently, Aaron, is that not only does it look at the conservation efforts that farmers are always conscious about, but it also looks at protecting the bottom line of farmers. And I know you looked at the efficacy of pre and post emergent herbicides, and so kind of talk about this study that you guys have done and how it all came to fruition because it's such a great story.

Aaron:

Well, it's really an interesting one because this marks, I think, in May of 2021, this will be my 28th year that I've been here. And for all the years that I've been here and even well before I arrived here, the weed science program here has done what we refer to as our Herbicide Evaluation Program. And essentially, what we do in this program is we look at various treatments predominantly that industry has, and we look at those on various weeds species and then in comparison with other treatments, other company programs, for example. It really lets us see a product, a pre-mix, a new active ingredient in multiple environments. And so it really allows us to get a look at it many times even before it comes into the marketplace. So we have a good idea about what its strengths might be, what its weaknesses could be, what its crop injury potential can be. But really, the history of the program is that we collect a tremendous amount of data from these various evaluations.

Aaron:

We spend literally weeks and weeks and weeks each growing season, not only getting these experiments established in the field, but evaluating them. And so, for all of these years, we have all these data from about 25 to 30 years-worth of trial evaluations in our evaluation program. And we publish the results annually, so anybody can look in and see how these products perform. But beyond that, we really did not use these data very much. And so, I've got a weed science colleague, Dr. Marty Williams who works for USDA-ARS at the station here at Urbana. And Marty, he's a big thinker, he thinks about things quite a bit differently than what I do. And that's not a bad thing, trust me.

Aaron:

But he and I, two, three years ago, we having one of our hallway conversations that we frequently have, and he was just then getting into working with large data sets. And I just said, "You know Marty, we've got this Herbicide Evaluation Program data set that has decades worth of information in it that we really haven't used that much past the year where we actually collected the annual data." And I said, "If you're interested in it, we could make all those available to you to maybe try to mine something out of there. Can you look at did herbicide X perform better than herbicide Y under, let's say, limited moisture conditions. Or was herbicide Z always more effective against weeds species P, for example, compared with herbicide B?"

Aaron:

And so that really got the wheels turning in thinking about what we might be able to do with this large data set on weed control. And so long story short, our student is just basically very close to finishing his PhD dissertation. Now looking at how he has analyzed various aspects of these data that looked at weed control, not just in one season, but actually over about a period of 25 years. So a long-term look trying to look at modeling what we may expect in the future based on what we have seen in the past.

DeAnna:

When you look at the curve balls mother nature has thrown us in the last five, 10, 20 years, no growing season is alike. And you have said that multiple times on different occasions.

Aaron:

Yeah. And really, what this analysis has let us do is be to look at multiple factors. For example, most of what the student's project included were data sets that included yield. So corn yield and soybean yield. And so if we can identify what are the best predictors of optimal crop yield in a given year, given the fact that weeds do nothing to increase crop yield, all they do is decrease crop yield. And just kind of give you an idea, if we look at the best predictor of optimal yield, it was basically how good was the weed control late in the growing season. So were we able to have products that gave us effective weed control for a certain period of time? No big surprise right there. But he was also then trying to look at the variability now in the climate, in the weather. We predict that there's going to be differences in precipitation in the next 20, 30, 40 years into the future, there's going to be differences in air temperature.

Aaron:

And so by looking at this data set over a 25 year period where there is differences every year, he's able to pull out individual factors that explained a lot of the variability in terms of crop yield at the end of the year. And so for example, one finding that he had, we always think about earlier planning corn may have a better chance for higher yield potential than something that's planted later. And I think those data actually exist that support that statement. But if there's limited weed control, for example, in a climate that's going to be different in 20 years, what he was able to find is that earlier planting doesn't always benefit corn yield when there are weeds that are not adequately controlled. Matter of fact, his analysis showed it could be better to delay planting a little bit in terms of having more weed seeds that have germinated and those plants could be either chemically controlled or killed prior to planting corn a little bit later on into the season.

DeAnna:

What did he find when he looked at soybeans?

Aaron:

I guess a lot of the same general trends were there. There were some things that really weren't terribly surprising. For example, in either a corn product or soybean product, if we put it on to the soil surface and we don't mechanically incorporate it, we need that precipitation to move that into solution, so it works more effectively. But if you look at a predicted change in precipitation into the future, for example, I think a lot of the models suggest that we're going to see more precipitation, but the distribution is going to be different. And I think many of the models suggest that we're going to see wetter and wetter springs followed by drier summers later on in the growing season.

Aaron:

So if we do need moisture, for example, for a soil residual herbicide to work optimally in soybean, I think the probability of getting that moisture would be higher in the future, but conversely, what happens if we get too much? For example. And we move that herbicide too deeply into the soil profile, maybe unfortunately it moves out of the field through a runoff effect. So looking not only at what's the minimum amount of precipitation required, but what could happen into the future if the precipitation tends to be more intense and a little bit more on the spotty side, for example.

DeAnna:

Well, when you look at the last few springs we've had, I think the farmer's dilemma has been, "Do I plant early when I can get in there when it's dry enough to get my equipment into the field without getting stuck or causing more compaction issues. And then do I replant after the rainy season? Or do I wait?" And I think it's a catch 22 because you only have that certain window as we know across the Midwest to get the crop in. And so then when you look at all of these things you can do with seed, whether it'd be seed treatment or pre-emergence herbicide, all of those things, not only do farmers look at that planting window, but they also look at all of those things adding up and then looking at the profitability of the crop.

Aaron:

Oh, most definitely. Yes. And we've always told folks that when it comes to weeds... And I think we made this comment a little bit earlier in our conversation here, but I've never seen one published study that shows that the presence of weeds ever increase crop yield. It doesn't happen that way. These things that we call weeds are basically, they're plants. And they have many of the same minimal requirements that a corn plant does, that a soybean plant does. They all need water, they all need nitrogen, they all need sunlight, for example. So those resources that are used by these competing plants, these things that we call weeds are basically resources that the crop can't use. And so all the expenditures that farmers have to try to control these weeds, they're never going to... And the way I present this is I'll tell somebody, in 28 years of doing this gig, I've never increased a farmer's yield by one bushel. Never have. Because I'm in the yield preservation business.

Aaron:

So if we can manage these plants that are competing for these limited resources with the crops, that's going to allow that crop to express its inherent genetic yield potential. The plant breeders, they're the ones who increase your yields. We're in the yield preservation business by controlling these weeds. And so the investments in weed control, whether it's a herbicide, whether it's a cultivation, regardless of what it is, that's basically an investment in allowing that crop to try to achieve that maximum genetic yield potential. And so if you look at your farm spreadsheet, you got your expenditure columns and you got your revenue columns. And when it comes to weeds, that expenditure column is pretty directly related to that revenue column because you can cut that expenditure all that you want to, but there's going to come a point, unfortunately, whether another incremental decrease in expenditures may not allow that crop to express that yield and that revenue column is going to suffer.

DeAnna:

Well, let's hope that we have a somewhat normal growing season, whatever that is.

Aaron:

Whatever that is these days. Yes, I agree.

DeAnna:

As we head into April, what's your advice for farmers as we get ready to gear up for planting season? What's your hope for this growing season?

Aaron:

We certainly hope everybody remains safe and healthy. That's always number one priority. We commented earlier about the fields getting some color to them. Our winter across much of Illinois, I think it was probably described as mild in many instances. Now February, we had quite a bit of snow cover. But even with the snow cover and the very cold temperatures, I think the survivorship, or maybe we should say the mortality of some of the winter annuals is probably pretty low. And so in other words, I think we're going to see a fairly robust stand of weed vegetations in the fields before we actually get to a position where we can either do tillage or burn down application. So certainly given the challenges that we face, not only with winter annuals, but we've talked for years about herbicide resistance that we see in both our winter annuals and our problematic summer annuals.

Aaron:

Again, it's really imperative that we try to get everything controlled before we put any seed in the ground, whether that be a good tillage operation, whether that be a burned down herbicide application, we really want to try to avoid the scenarios of planting into any green weed vegetation if we can. There's going to be instances, obviously, where a farmer says, "Look, I got to go. I can't get a spread. I got to get a plan." And we get that. But we certainly hope that those are not the majority of the instances that we'll see this year.

DeAnna:

Absolutely. Aaron, is there anything else that you would like to add that maybe I left out?

Aaron:

Just again, we're going to continue to face some of our challenges. We will talk, I'm sure, in the future about some of the issues that we continue to see evolving in some of our weed populations that are not really responding very effectively to herbicides that once were very effective for their control. And these issues are not going to go away, they're going to get a bit more problematic as we continue to move forward. But of course, the good news is we do have the ultimate solution for this and we've known this for many, many years. And I think now is really the time where we've seen a lot more interest and farmers really thinking about what else do we need to do in addition to just herbicides to try to get these summer annual species under control.

Aaron:

And that's very hopeful because I think ultimately at the end of the day, there's going to be a realization that we're going to continue to use herbicides on virtually all of our acres. But I think our weeds are finally going to reach the point where they dictate we're going to have to do something in addition to that to try to ensure that by the end of the year there's very little, if any, weed seed that's returned into the soil.

DeAnna:

And that all starts with diversifying your modes of action.

Aaron:

Again, it certainly is useful and helpful to understand what remains effective, what is no longer effective because of evolve resistance. But I think I probably have said this before, it's kind of a far-fetched idea to think that we can solve a herbicide generated problem with a different herbicide. It may be a temporary solution, for example, but in the long-term the weeds are going to continue to evolve. So what else can we do to try to ensure that by the end of the season there was no survivors in these fields? There's some things that we can think about it, it doesn't necessarily always have to be a 180 degree turn in what we're doing. Let's just say hypothetically that...

Aaron:

Unfortunately, in 2020 you had what we'll call the train wreck year, and nothing worked. And at the end of the year, it was hard to see the top of the corn plant because all the waterhemp or Palmer amaranth was even as whole as the corn was. Well, you had a tremendous amount of seed that just went back into the soil seed bank. But what can we think about then? How would you even go about trying to begin reducing that soil seed bank? And again, it doesn't happen necessarily the... An idea that takes a super computer to come up with a solution. And one thing you can always do is just let seeds do what seeds do best, and that's germinate. And by that I mean, well, what does that mean? Well, maybe that train wreck year or that train wreck field from last year, maybe you don't want to plant that one first this year.

Aaron:

Maybe you can actually have a luxury, so to speak, of putting that last on your calendar to plant that field. And you know what? 2021, great spring, you got everything in, it was timely, it was perfect conditions to get everything planted. But you got this one field left that was a train wreck last year. What are you going to do with it? Well, you look at the calendar and you're really not late yet. Why not just let it lay there for a little while longer? Every day you're probably going to have hundreds of thousands of additional weed seeds that are germinating. Let them germinate, let them come up through the soil, make sure you control them before you plant. But by simply delaying something like planting by a few extra days, you could help really deplete millions and millions of seed from the soil seed bank, and it really didn't cost you time to do it. It's just an example, really, of things to maybe think about in addition to our more traditional herbicide applications that we can do.

Aaron:

For example, I don't like to walk soybeans. I did it when I was a kid, it built a lot of character. I just got a lot of blisters out of it. But that's a very effective way to try to control the straggler. If you've got a train wreck of a weed problem, you're probably not going to be able to find enough warm bodies that have an active pulse rate to try to weed out all those things by hand. But on the other hand, if you got a field that looks really, really good, but you've got one here and there and scattered across 40 acres, that's an ideal candidate to spend a little bit of time doing a little bit of infield scouting and remove those plants before they get to the stage where they've got viable seed.

Aaron:

That one straggler, that one female waterhemp that's at the end of the 35 acres, she's probably not going to cause you a lot of yield penalty or lost yield in the soybean or corn, either one. But what happens if she's the one female that has the seeds of the new generation of resistance that you've never had before, but now you've got it? And if you had removed her before she had those viable seeds, you have just delayed that evolution almost indefinitely. So again, there's a lot of different ways that we can try to do these things. And it's just going to require a bit of maybe a willingness to try to have a more integrated type of approach.

DeAnna:

And diligence.

Aaron:

And diligence, you bet.

DeAnna:

Very good. It's always so great to visit with you.

Aaron:

Yep. Happy to chat with you.

DeAnna:

Dr. Aaron Hager contributes to increased crop production through development and implementation of integrated weed management programs. His research helps identify and manage herbicide resistance in the most aggressive agronomic weeds. To reach Dr. Hager at the University of Illinois, you can call area code (217) 333-9646. Or send him an email at Hager@illinois.edu.

Jodi:

Thanks to DeAnna Thomas and Dr. Aaron Hager, to the Enlist Weed Control System for sponsoring this podcast, and thank you for listening. For Successful Farming, I'm Jodi Henke.