Weeds AR Wild Series, Season 2 Episode 9. 
Title: Weeds AR Wild Series, S2 Ep9. Non-chemical methods for weed control in cotton and soybean 
Date:  April 14, 2022

[Music]:  Arkansas Row Crops Radio providing up to date information and timely recommendations on row crop production in Arkansas.

Jason: Welcome to the Weeds AR Wild podcast series as a part of the Arkansas Row Crops Radio. My name is Jason Norsworthy, Distinguished Professor of Weed Science for the University of Arkansas System, Division of Agriculture. And today I'm excited to be joined by our Extension Weed Scientist, Dr. Tom Barber. Tom, it's great to have you on our podcast today. And I think today we're going to talk about some non-chemical approaches to managing weeds, some things that we can do outside of the box or things, again, other than just spraying to try to get some of these weeds under control.

Tom: Well, yeah, Jason, glad to be here. And I think it's a great topic. You know, the last time you and I were on a podcast we talked about all the resistance we had, especially in cotton and corn, soybean acres. And so, I think it's really good to focus on some things we can do other than chemical to help get us in a little bit better management situation.

Jason: Let's start with the fact the two of us have a project over at the Lon Mann Cotton Research Station, where we've been looking at over, I guess now the last three years, integrating practices into cotton. We've been talking looking at specifically cover crops, a rye cover crop. We looked at actually a one-time moldboard plow, and we're integrating that in with herbicides. And we've got a student that has summarized that work, three years in, and it's really exciting to see some of those results and the impact that they have. And the plow treatment that we looked at was a one-time moldboard plow back, I guess it's been four years ago this past fall, well three years ago this past fall. And what we, just again – some take home from what we saw in this research is that, the first year we had a very, very strong moldboard plow effect. And what we're seeing there is we'll get about 75% reduction in pigweed emergence the first year and then that effect diminishes over time. And actually, when we looked at the data three years in, we didn't see a significant effect last year. And this cover crop effect when you put it on top of the moldboard plow, really you're building on two different strategies. And at times we've seen better than a 90% reduction in pigweed emergence when you combine cover crops with that of a one-time moldboard plow.

Tom: Yeah, really that was amazing to me to see that first year, and when we talk about this project it was, really you and I discussed – you've had several graduate students working on different pieces of this puzzle, I guess. You've had some that covered tillage practices. You've had some the covered cover crops and which cover crops work best and the biomass needed and that kind of thing. But putting all those practices together and seeing them in one project and in the field and how they can benefit us, especially on the pigweed front, was really EYE-OPENING to me.

Jason: Well, also what excites me about this, when you talk about moldboard plow, I understand that there's a reluctancy for someone to drag that out. But I mean, we're dealing with populations, very, very pigweed populations. And, you know, we've got some locations throughout the state, as you mentioned earlier, that's resistant to a wide assortment of herbicides, don't have a lot of options. And that moldboard plow gives us an opportunity to get that soil seedbank back down low. But the component here that really excites me is this cover crop, because when we put that cover crop on top of that bed and we're going to bed all of our cotton here in Arkansas, when we bed that ground up, that cover crop has helped keep that bed intact. And we haven't lost that bed even though we had that one-time moldboard plow event now three, going on four years ago. We've got the same beds. We haven't run any type of tillage through that since then. We're still planting on those same beds that are intact because of all that residue or cover we have on the soil surface.

Tom: Right. And that just goes back to reduced time and energy to get the seedbed ready to plant. When we have something that protects those beds, it's like you said, we're not talking about every year go in there and moldboard plow. This a once in three years, and I know we're getting into the data here in a minute, and that's kind of what the data is showing us. We might need to do it, if we get to a situation where we really have to start considering implementing this type of tillage. It's not going to be an every year necessity, I don't think.

Jason: No, that’s correct. Again, by year three, we had about 37% reduction in Palmer amaranth emergence this year, and so that's diminished over the last three years and it's about time to come back in there and implement another moldboard plow. But also, when we talk about cover crops, some work better than others, at least in the research we've done. What we've seen here is, I'm a big fan of cereal cover crops. When I say cereals, for me it's cereal rye. I like cereal rather than wheat, just partly because cereal rye is going to produce a lot more biomass. And the more biomass we get on the soil surface, the better we're going to be able to suppress emergence. We've looked at legumes in the past. There's a lot of interest in legumes because of the nitrogen credits that you get with those legumes. But those legumes have a low carbon to nitrogen ratio. What we've actually seen is, it might be a function of just the nitrates being released from those legumes. At times, we'll see more pigweed in the legume plot where we don't have legumes out there. So I understand there's a lot of excitement about trying to put a legume out there, but that just has not worked for us, at least as it relates to pigweed.

Tom: No, and I think most growers that are farmers in the state that I talk to that have tried cover crops a little bit. I mean, generally they're going to start with cereal. I think I've heard Dr. Trent Roberts call it a kind of “a training wheels type cover crop,” – the cereal rye. It’s easy to establish. It's easy to terminate, and that's what I like about it. And like you say, it produces the biomass we need to help us with the pigweed, probably more than any of them. So, cereal rye for me, I think if I was a farmer listening to this and wanting to try it for the first time, that's definitely the one I'd probably try first, especially on my acres.

Jason: Well, you know, there's a lot of excitement. I hear folks talking about these blends, and almost to some extent these wildlife blends, and using some of those today. And, the issue that I see with that is, we've actually found is some Brassicaceae cover crops can be allelopathic to cotton. So you better know what works and what doesn't work from a toxicity standpoint. Yeah, it might help suppress pigweed, but you better have something that's not going to be negatively affecting your cotton. And the other thing that concerns me, when I start having these blends of seven, eight-way different species mixtures, some of these are going to be difficult to kill. For instance, a glyphosate/Dicamba burndown. And some of this is going to be more challenging to kill than some other species that we've got in that mixture. We just need to make sure we've got something that we can definitely feel confident that we can get it established and that we can control. Then the other thing I tell folks is, when you're talking about cover crops and using those, start out with small acres, don't go out and put all your acres into cover crops. Ease your way into it. I think you're going to be pretty impressed with what you can do with some of these cover crops.

Tom: Absolutely. And, this time of year, of course we're getting ready to plan, the big question is termination timing. When do I spray my cover crop to plant my cash crop. So, can you go over kind of what y'all have done in this research as well as what you've seen in the past?

Jason: Yeah. So we've done some things there we've looked at. We still have some work ongoing. I know you have also have some work ongoing. Corn as well as soybeans, where we've been looking at termination and different termination timings. Now, by delaying that termination, and it's all about trying to get as much biomass out there as possible. And the more biomass we can get, the more that we're going to be able to sustain that biomass throughout the growing season. Generally speaking, what I've recommended to folks is, I try terminating about two weeks prior to planting. I want to make sure that the cover crop is desiccated when I plant. But now having said that, you know, we're looking at planting green. There's a big push to try to plant green. I'm not going to sit here and say that's not going to work for us. The beauty of planting green is you're definitely going to have more biomass out there. And again, the more biomass we have, the more weed suppression that we have associated with it. I know our good friends, the entomologists, cringe when we start talking about planting green, even two weeks prior to planning a termination date - sometimes they kind of turn their eyes up and look at us. I know they like an earlier planting date, but you know, Dr. Barber, with the insecticides that we've got on these seed treatments, and I don't care what the crop is today. We've got some pretty strong insecticides out there that we're using on these seed treatments. I've had very, very good luck. If I'm within two weeks of planting and I terminate, I had very good look out of my cover crops.

Tom: No, I agree with that. 100%. That's what we've seen, too. And I think from an entomologist’s standpoint, and we had a meeting earlier today talking about some of these things, but there's just a lot of unknowns. And when there's unknowns, obviously that leads to uncertainty. When we give recommendations, whether it's for insects or pests or weeds, we want to have all the experience we can get with it. So there's still a lot of unknowns there, I think, as far as Green Bridge and that kind of thing. But I'm with you. Honestly, as long as we're at two weeks, I haven't seen any issues, especially going from a grass cover crop to a broadleaf cash crop. If we're talking about going from cereal rye to corn, we might need to focus on insects a little more. But we're going from grass to a broadleaf crop, usually we're going to be okay with that.

Jason: Well, and so really again, just kind of if we think of cover crops, the goal there is to get some cover on the surface. And I want to talk a little bit about that when we're talking about non-chemical approaches, because there's several different ways you can get cover on that soil surface. One has to do with row spacing. We've got a lot of beans, for instance, in this state where we're planting on a 38-inch row. It's a single row. I'd much rather see a guy plant twin rows because a twin row is going to get the canopy about seven days sooner. And what we've seen in our work is when we get to about 90% light interception or 90% ground cover, whether it be a cover crop or whether it be a crop canopy formation, we see a substantial reduction in weed emergence. Actually what our data has shown is, a lot of folks are of the opinion – it’s really light that is triggering the emergence of these weeds, but instead it's the temperature fluctuation that's occurring on a daily basis. And if we've got a good cover on the soil surface, the daily temperature only fluctuates about seven degrees at about 90% light interception. And that is a trigger to the weed that it is not in an environment that's conducive to success – that being able to germinate and then eventually reproduce. If you go out and you look at a bare soil today, just general bare soil, you're going to see a daily fluctuation in temperature at about probably a half-inch to an inch. It’s going to fluctuate about 20-25 degrees. And so that is the trigger in a lot of instances that keeps these weeds from germinating and helps us successfully grow a crop and really takes the selection pressure off of some of our herbicides.

Tom: Well yeah, that was kind of the eye-opening thing to me because I was probably one of those individuals in the, “well it’s taking out the light and therefore it's not triggering germination,” before we started all this work. But, when we first started with seeding rates, I think we started with cereal rye somewhere around 100 pounds to the acre. And now we’ve backed that down. And so the biomass, I guess, doesn't have to block out all the light. It just has to do good enough to prevent that big swing in temperature fluctuations, is what we're hearing now.

Jason: That is correct. Again, I mean I don't need just a ton of biomass. I mean, the beauty of the cereal rye is the high carbon and nitrogen ratio. And so for that reason, the biomass that I have a tendency to produce there, I've seen that it stays intact throughout most of the season. And, something else that I'm going to want, I think me and you were talking a couple of days ago about, is moving forward I'm going to look at some intercropping. You know back about 20 years ago, there was a lot of buzz about intercropping, and intercropping is just a technique. If you take a look at wheat, and I know wheat prices are up, hopefully they'll stay up for a while. But if you take a wheat crop and you come in where you’ve got about a 12-inch wheat crop, there's actually been some research to plant soybean into that wheat crop early about this time of year. Maybe even a week earlier than this. And with that, those soybeans are going to emerge. And when you go in and you harvest your wheat in early June, we potentially at that point have a soybean crop that’s up V1, V2, and that crop is going to canopy a lot sooner. And with that, you have cover on the soil surface almost year-round. It does a tremendous job based on what I've seen in the literature in suppressing weeds.

Tom: Well, I think to me, that's an intriguing idea. We keep coming back to these cultural methods that have been done in the past. I mean, cover crops, for example, it's not a new thing. Deep tillage is not a new thing. But we keep coming back to those just because we know the next chemistry for pigweed is several years down the road. Really, realistically, I mean, from a new mode of action standpoint. So it's critical that we look back at some of these cultural methods that worked in the past to see if we can implement those to help us at least during this period of time where we may run out of options POST for Palmer pigweed.

Jason: I'll tell you something else that I think we can use to our advantage is, if you take your weed of choice – barnyard-grass, Palmer amaranth, whatever the weed might be, there is a peak period in the growing season in when that weed emerges. Yes, I'll be the first to tell you that Palmer emerges over probably about a six-month period, but there is a certain time of year that you're going to get greater emergence. And, just looking at planting dates. If we go out and we think about corn, generally speaking, we don't have as much of a pigweed issue in corn. And I'm talking about early planted corn. It’s what we do in soybeans that are planted mid-May, because really mid-May/early June is the peak period of pigweed emergence. And you're planting right at the same time that crop is emerging and that's an issue that we have to deal with. So I just want everyone to also remember, we've got a lot of flexibility. If you look at soybean today, there's a lot of flexibility as to when you can plant soybeans. Moving that planting date up, there's a lot of interest in doing that. And I think there might be some value in terms of helping to protect us against these pigweeds that are out there emerging in mid-May and June.

Tom: Well, I agree, and I think we've seen a great benefit where we have, on the growers that have narrowed their row spacing, like you're talking about, and moved and shifted their planting window to earlier, for various reasons. But especially in a weed management scenario, it is a big benefit. When I plan my plots, as I'm evaluating herbicides for weed control and efficacy or whatever, I don't want to plant those very early because I'm not going to have my weed population. So, that fits right into what we're talking about here. So, hopefully this rain that's moving through now, we’ll get some good weather after this and can get in and start planting a lot, especially if our soybean acres. Cotton is one of those where we are limited somewhat to our planting window, because those soil temperatures have to be right for everything to work right. But with soybeans, absolutely. I think we can push the envelope more than we are right now.

Jason: Yeah. And so on top of that, I think another strategy that really comes to my mind is just preventing seed production. You know, we've talked about zero tolerance. I mean, that is a concept that has been around for many years now here in Arkansas and back your predecessor, Ken Smith, he was a big proponent of it. And I'm still to today a big proponent, because when you take a look at preventing seed production – and I'm not saying that you've got to go out there and you’re going to have to hand weed every acre. But if we can utilize as many strategies as possible from keeping these weeds from going to seed it's going to benefit us next year, because really what we're doing is we're bringing down the soil seed bank.

Tom: Absolutely. You know, we talked about our cotton project earlier that we've got looking at this. But we've also got one in beans where we're implementing these strategies and the Seed Destructors, the RedeKop Seed Destructor, that we have right now – like you have one up in northeast Arkansas. I have one at Newport there. So, you know, I think all of that when we look at just implementing multiple cultural strategies and in soybeans especially, we can get two or three in there pretty easy. In cotton, like I mentioned, it's a little bit harder. But where we can, implementing these multiple strategies, cultural, something other than chemical, we're going to be better off in the end.

Jason: Yeah, I've heard it referred to as the mini little hammer approach. I mean, none of these strategies are going to be equivalent to a herbicide, but when you start stacking them on top of each other, it's pretty impressive – how much weed suppression, reduction in emergence and suppression of growth you can get when you have multiple strategies that you're utilizing. And like I said, some of my work where we've actually taken herbicides out of the system and we've gone in and we'll count. We’ll hand weed these plots. We can get better than 90% reduction in weed emergence over the course of a growing season just using some of these strategies we talked about today.

Tom: Oh, absolutely. And I keep remembering all those meetings we had when those farmers and growers from Australia came over and talked about the situation they are in with rigid ryegrass, and now they have no chemical options available. I would just, I'd love to see some of these cultural methods implemented before we get to that point with Palmer amaranth. And, I don't want to be a doom and gloom guy here, but the writing's on the wall for me on what's going to happen over the next five years probably.

Jason: Well, it is an eye-opening experience. I had an opportunity in 2013 to spend about three weeks in Australia. When you're standing on a farm and the guy is sitting there telling you there's not a single herbicide, I can spray that's going to control rigid ryegrass. But, what is also interesting is, those guys are not out of business today. You know, their back was against the wall, and they came out swinging. And, a lot of these strategies that we're sitting here talking about, they were very innovative, these guys were. And they've had some success managing ryegrass in the absence of effective herbicides. So I tell folks at the end of the day, I'm confident that we're going to have success. I don't think that pigweed is going to put us out of business, but I do think that we're going to continue to see pigweed evolve, resistance to the herbicides that we have that are still effective. So, we’ve got to try to get in front of this if we're going to keep herbicides as being a tool in our tool basket.

Tom: Absolutely. Absolutely.

Jason: Are there any other strategies that we haven't discussed at this point that you'd like to touch on today?

Tom: Not really, from a cultural standpoint. I think, though, just as important, if there's one thing that comes to my mind when we do have to – you know, we are still implementing herbicides and we will always implement herbicides into these programs. But I think, you know, we preach it all the time and we talk about it every time we have a podcast, but multiple residuals and timely POST applications. It goes hand in hand with all of these cultural management practices that we're talking about here.

Jason: Now, one thing I'll add to that is, start clean. And, if I don't have tillage running in front of the planter, I've got Gramoxone or some other herbicide that's sitting there just ensuring that I don't have weeds up when I plant. Because if you have weeds up at the time of planting and you're not clean, you're going to be behind the eight ball and you're going to have difficulty getting back in front of it.

Tom: No, absolutely. Great points.

Jason: So well, hey, I appreciate you being with us today and talking about some of these non-chemical approaches and some of the selection pressures they can take off of our herbicides. I hope our audience has enjoyed this discussion and appreciate them for being with us on this episode of the Weeds AR Wild podcast series on the Arkansas Row Crops Radio.

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