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This week’s podcast, sponsored by Montag Manufacturing, features Chris Proctor, Weed Management Extension Educator, University of Nebraska.

Proctor will discuss how cover crops help with weed suppression, how to incorporate covers into an integrated pest management program, the relationship between tillage, herbicide resistant weeds and cover crops, and more.

The Cover Crop Strategies podcast series is brought to you by Montag Manufacturing. Montag precision metering equipment is helping producers achieve their yield goals while saving on seed and input costs. For establishing cover crops, Montag’s family of seed platform equipment adapts to a variety of major brand delivery systems that will conserve seed and nutrients along with soil and water. Explore new options for your production and conservation goals with your Montag dealer, visit www.Montagmfg.com or call Montag at (712) 517-2775.

 
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The Cover Crop Strategies podcast series is brought to you by Montag Manufacturing.

Montag precision metering equipment is helping producers achieve their yield goals while saving on seed and input costs. For establishing cover crops, Montag’s family of seed platform equipment adapts to a variety of major brand delivery systems that will conserve seed and nutrients along with soil and water. Explore new options for your production and conservation goals with your Montag dealer, visit www.Montagmfg.com or call Montag at (712) 517-2775.

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Full Transcript

Sarah Hill:

Welcome to the Cover Crop Strategies podcast. I'm Sarah Hill, associate editor. MonTag precision metering equipment is helping producers achieve their yield goals while saving on seed and input costs. For establishing cover crops, MonTag's family of seed platform equipment adapts to a variety of major brand delivery systems that will conserve seed and nutrients along with soil and water. Explore new options for your production and conservation goals with your MonTag dealer or on the MonTag manufacturing website. Today, I'd like to introduce Chris Proctor, weed management extension educator with the University of Nebraska. Chris will be discussing using cover crops in integrated pest management programs. Welcome to the podcast, Chris.

Chris Proctor:

Yeah. Thanks Sarah.

Sarah Hill:

To get us started, why don't you tell us a little bit about yourself?

Chris Proctor:

Yeah, absolutely. So I'm an extension educator, as you mentioned, which means I spend a lot of time interacting with growers around the state of Nebraska, so a lot of different things related to weed management. But I've had particular interest in using cover crops these last number of years. It is just an additional tool for managing weeds, and so that's something I've been pretty excited about. I do a lot of extension outreach and some research, and I really enjoy working with students and that aspect of what I do as well. And so a lot of variety in what I do, but it keeps me busy and it's something I enjoy quite a bit.

Sarah Hill:

Fantastic. Well, we'll go ahead and get right to today's topic. Give us a general overview, how cover crops can help with weed suppression.

Chris Proctor:

Yeah. As I think about what are the mechanisms or what's the value of a cover crop in terms of suppressing weeds, really it's about resource competition, if I was to describe it broadly. And so you have different plants sharing the same space. In the same way that weeds can compete with our crops for nutrients and light, water and so on, I think cover crops can do the same to weeds. And so if you can establish a cover and get it growing in your system, it can effectively suppress weeds, keep them from either emerging or slow their growth down. Often when I think about it, really, there's a couple of ways that I think about weed suppression. So we've seen in different work that's been done that weeds, excuse me, that cover crops will suppress weeds by, one, delaying the emergence of those weeds.

Chris Proctor:

So just by having a cover crop there that changes the microenvironment where those weeds are germinating, and so you can delay the timing that those weeds emerge into a different part of the season. So a great example would be Palmer amaranth. There was a nice study done out of Kansas, where they showed by having a serial cover crop, wheat in this instance, they delayed by almost a month, 50% of their Palmer amaranth emergence. That was from about mid may to about mid June. So that was pretty interesting finding. Another way that I've seen cover crops suppress weeds is they'll reduce the weed density, and so there's just fewer weeds present. So you have cover crops, it's not that all the weeds go away, but the ones that... There's just fewer weeds that tend to emerge, not as competitive, or they don't have as many emerging where the cover crop is present.

Chris Proctor:

And one of the other ways that cover crops offer some suppression, by reducing weed biomass. And I think about that is the size of the weeds. And so just having that competitive cover crop, you can reduce weed size. And we know from a lot of different research, if we can reduce the size of the weeds, that helps some of our other tools be more effective. And so if we can target managing those weeds when they're small, we tend to be more successful. And so those are the big three ways that I often think about when I think of suppression.

Sarah Hill:

Okay, great. So help us understand how cover crops can tie into the bigger picture of an integrated pest management system.

Chris Proctor:

Yeah. No, absolutely. I think that's the key, is it's part of the system. I guess I had mentioned that briefly, but really, to me, I like to think about an integrated management approach as having multiple tools in a toolbox, and so we have a lot of different tools for managing our weeds. Herbicides are very commonly used in our cropping system and are fairly effective in most cases, but we also recognize that if we overuse them or don't use them in the right ways, we can develop herbicide resistance. And so that takes a tool that was once effective and renders it ineffective, and so we lose that tool from our toolbox. So when I think about cover crops, it's about adding a tool back into our toolbox for suppressing weeds. So instead of asking the herbicides to do all the work in suppressing weeds or controlling weeds, we can get some of that workload, or we can transfer some of that workload, say, to a cover crop.

Chris Proctor:

So let's say we get 50% suppression from a cover crop. Well, then if we come back with an herbicide at that point, we only need 50% more effort from that herbicide instead of 100%. And so that's just one way I like to think of about it, is can we diversify our system? Can we add more tools to our toolbox? Can we ask each tool to carry a little bit less of the load? So when you spread it across, all of them, they remain effective longer so we don't lose our tools to resistance or things like that.

Sarah Hill:

And maybe you kind of alluded to this a little bit in this previous question that I asked, but what is the relationship between tillage, herbicide-resistant weeds, and then cover crops?

Chris Proctor:

Yeah, it's helpful to think through these different relationships, and as best as we can understand, what is leading, what's causing what? If you can put it that way. And so I know in the state of Nebraska, we have a pretty high percentage of our acres that are now no-till, managed using no-till systems, and there's a lot of benefits to going to no-till. There's a lot of advantages to using that system. If there's a disadvantage, it's we lose tillage as a tool for managing weeds. So tillage tends to be a pretty effective way to control our weeds. In a no-till system, a lot of those weeds now are managed primarily, or historically are primarily managed by these herbicide programs. And so burying the weed seed, you're not mechanically controlling those weeds with the tillage implements.

Chris Proctor:

And so now we're relying pretty heavily on our herbicide management programs to pick up what tillage was once benefiting us. So again, do you think about cover crops as a tool to integrate back into that system? It could, in a way play the role that tillage once played in terms of an additional tool for managing our system. That would be one way to think about it. I'm sure there's others as well. And that's one thing I've learned along the way is there's lots of creative growers and agronomists out there that are trying all these different ideas and looking at these systems, but that's certainly one way that I've thought about it.

Sarah Hill:

So how does the planting date, as well as the location within the field where cover crops are planted, how does that affect their efficacy in helping control weeds?

Chris Proctor:

Yeah, so I would say the biggest driver of weed suppression with cover crop is their ability to produce biomass. So the more biomass they produce, the better weed suppression we get. So that's not to say that there isn't value to cover crops, there isn't other added value or reason to go cover crops from reduced biomass. But when it comes to weed suppression, biomass is really the driver. And so the more biomass we produce, the better weed suppression we get. So with that in mind, when we think about what drives biomass production in cover crops in a corn/soybean system, our limiting factor is often the amount of growing season remaining to plant, establish, and grow a cover crop.

Chris Proctor:

But we do know the earlier we plant in the fall, if we're going to use a fall planted cover crop, the more biomass we produce in the fall and then the subsequent spring. So it makes sense you just have more growing season available for that cover crop to grow. An earlier planting date in the fall will increase biomass, and we've tried different ways to accomplish that. You can interseed your cover crops late in the season with an airplane or a high clearance machine that's adapted to interseed cover crops down into a corn or soybean canopy before harvest. We've also tried planting earlier season maturity group corn or soybean, which would allow for an earlier harvest time. And this then would allow us to plant just a little bit earlier in the fall.

Chris Proctor:

So there's some different ways I think folks have tried and thought about planting earlier. Then the other side of it is, can you delay termination in the spring? So can you let that cover crop grow just a little bit longer in the spring until you terminate it and then plant your subsequent crop? We find in Nebraska that two weeks of time in the month of May can almost double your biomass production. So there's a lot of biomass production potential in that early spring. So once you hit May, a lot of our cereals in particular, cereal rye is very commonly grown. There's a lot of growth potential just by delaying, say, two weeks, from May 1st to May 15th. So again, biomass drives it, but planting date is really one of the key components to producing biomass.

Sarah Hill:

Great. So talk a little bit about allelopathy in regards to how cover crops can provide an allelopathic effect on weeds.

Chris Proctor:

Allelopathy is an interesting one to me. It's something that I've thought quite a bit about, tried to track down a number of research studies. A group of us put together a review paper recently, thinking through allelopathy and the implications and some of the other research that's out there. And what we've found is that there's not a lot of field research when it comes to identifying allelopathy specifically. It's discussed, but it's really hard to track down in a field setting. So there's a lot of laboratory based setting studies where they can extract the allelopathic compounds and test how what effects they might have on seeds. It's a little bit harder to track that in the soil. There's just lot more going on and the concentrations are different and all those things. So that being said, there are allelopathic compounds that different cover crop produce.

Chris Proctor:

Cereal rye, rye grasses are one that are often noted for their allelopathic potential. The mustards are another one that have some of that potential. I think the one thing that we note is the larger the seed of the weed or the crop, the less allelopathy seems to influence those plants. And so often we don't think our crop species are very often influenced by allelopathy, because they're relatively large seeded corn, soybean, for example. But if you have a really small seeded weed like Palmer amaranth or water hemp, for example, those small seeded weeds, where the seeds are near the surface, or mare's tail is another great example, horseweed those types of weed species. I think we do see some impact from allelopathy where those chemicals that those cover crops produce and are released into the soil can also help suppress those weeds.

Sarah Hill:

We'll be right back to the podcast, but first I want to thank our sponsor. MonTag precision metering equipment is helping producers achieve their yield goals while saving on seed and input costs. For establishing cover crops MonTag's family of seed platform equipment adapts to a variety of major brand delivery systems that will conserve seed and nutrients along with soil and water. Explore new options for your production and conservation goals with your MonTag dealer or on the MonTag manufacturing website. And now back to the podcast.

Sarah Hill:

How can using cover crops help minimize growers' reliance on pesticides? You've kind of alluded to how herbicides play into the picture, but what about pesticides?

Chris Proctor:

Yeah. No, I think there are some other benefits that the cover crops more broadly than just weed suppression. So I think it is important to note when you think about different cover crop species and their ability to attract either beneficial insects or predatory insects, I think there's been some work done that has shown that if you can increase those populations of insects, it can have a positive effect on insects that are often pest for a crop. And so cover crops can provide that post crop, if you will, to draw those different predators in. And usually we see a greater diversity of insects in fields that are growing cover crops than those without. And so just by having that broader diversity of insects present tends to have a pretty... It tends to be beneficial to the system as a whole. That's one way that I think has been recognized of cover crops' value and the system more broadly.

Sarah Hill:

Great. So what about herbicides? I know you talked a little bit about the relationship between herbicides and herbicide resistant weeds and cover crops, but how can using cover crops help growers save money then on herbicide costs?

Chris Proctor:

I think that's a really interesting question, and it's a question that I hear a lot of folks starting to talk about. I would say we're a little bit early still in understanding how these tools effectively fit in our system, in the sense that I don't know a lot of folks that are using cover crops instead of spraying an herbicide yet. But I think that's what they're striving towards. I think the goal is, can we identify what's the economic value of these cover crops? And can we really identify how much suppression are we getting from cover cops on these weeds, and does it allow us to maybe skip an herbicide application that we would've made otherwise, because we're getting good enough weed suppression? So I think people are moving in that, in that direction.

Chris Proctor:

They're starting to try that out as they get into the season, "All right. Maybe if I have enough residue, can I skip my post application? Am I comfortable with the level of weed suppression I'm seeing as that canopy is closing that maybe I won't apply that post-emergent application in my corn or soybeans where without the cover crop, I might typically do that?" And so I think folks are thinking about that. And I think as folks start to think about interseeding cover crops, so drill interseeding is becoming more a topic that I hear about and we've done some research on, and that's where we would interseed a cover crop into corn, at maybe the V3, V4 stage of corn early in the season to try to establish it early and see if we can't get enough cover crop growth to actually benefit weed suppression as we go into the season.

Chris Proctor:

And by doing that, does that provide a level of weed suppression that potentially could limit our herbicide program? No, I think the goal... I think the people that are really pushing for this, the goal might be, can we have a continuously growing cover crop throughout the season? So as the one cover crop is terminated, our cash crop or our primary crop is planted and they come back and plant a cover crop right into that to keep that cycle going. I think the closer we can get to that ideal, I think the more success we might see in being able to start minimizing some of the herbicides. But as of yet, I don't think it... It's not the tool to just straight replace herbicides, so I think it's, how does it fit in my system? Are there ways that I can make use of it in certain fields or certain settings where I know I have particular issues or certain goals I'm trying to meet? So that's a long way of saying, I think we're getting there, but I think it really depends on what we're doing and what our system looks like.

Sarah Hill:

Okay. Well kind of getting into the nitty gritty here of what a system looks like, which cover crop species have you seen are best suited for helping reduce some of those incidences of disease or nematodes or weeds, of course?

Chris Proctor:

So again, I think a lot of the benefits that we see on weeds in particular, again, is tied to biomass. I think diseases, it's a little bit mixed there. Too much biomass, you have the potential maybe to start creating a green bridge, depending on what your disease pressure is, where that disease carries from the crop to the cover crop back to the crop again. And so I think a little more care is often taken when thinking about disease management, or if you know you have a lot of disease pressure. But I guess what I'm trying to get at is species selection depends a lot on your goal and what are the windows of opportunity within your system. And so if you're a corn and soybean grower, you kind of have what would be maybe called a traditional cropping system. That window of opportunity is really once you harvest your corn or soybean until you plant that corn or soybean again in the spring. So it's a pretty short window.

Chris Proctor:

And in those instances, it's the winter cereal grasses that tend to be most successful. So instances where we've planted these highly diverse mixes in those settings, usually it's the cereal rye that survives and carries most of the weight of that mix. Most of those other species, either they don't emerge or they emerged and they die in the wintertime, or they just don't have a lot of growth in that window. But if we follow wheat, for example, which is harvested in July, that gives us a much larger window for establishing a whole range of cover crops. Behind seed corn, there's opportunities there to seed much earlier in the season. These interseeding opportunities that I had mentioned, where you're planting into your growing cash crop, I think you can establish more diverse mixes there. So I think there's value in these diverse mixes, but only if you allow yourself enough opportunity for those mixes to establish and grow and produce enough biomass to benefit. But if you're looking at really short windows of opportunity, I don't think the return on investment for those mixes is really there.

Sarah Hill:

All right. Great. So would you say that a cover crop mix is probably better than a mono crop?

Chris Proctor:

I guess I would say it depends. I would say not always, but there's certainly times where I think it probably is more advantageous. And we often think, and I think rightly so, that if we can increase diversity in our systems, there's a benefit to that. Diversity tends to improve resilience and our ability for our system to be managed through different environmental conditions and different things that come up in a season that we aren't always able to anticipate. So diversity certainly helps us in those ways, but I guess the key with mixes is making sure that the system is set up, that those mixes are actually performing in a way that they're benefiting us.

Chris Proctor:

I don't want to just keep reiterating the same point, but if we don't have enough season available for those mixes to establish and grow, they tend to be more expensive, and I would say your money's better spent really focusing on one or two species that you know will be successful for that part of your season versus trying to push a mix that might not be successful. So it's really thinking about your system and where do they fit, what are the goals that you're trying to achieve. So there's certainly soil health goals and nutrient goals that might be of interest beyond just weed suppression. So if you're interested in those things, you want to think about that as well.

Sarah Hill:

Sure. Okay. So how can growers ensure that cover crops compete with weeds and not the cash crop?

Chris Proctor:

Yeah, I think that's a good question that certainly needs to be thought about. And so I think it depends. Soybean tends to be more forgiving, I think would be the way maybe I'd put it, than corn. So a lot of times folks can plant their soybean into a green and grow and cover crop before they terminate it. And soybean tends to emerge through that and be just fine, where a lot of times corn really struggles in that type of planting environment. And so I think if you're new to cover cropping and you haven't used them a lot, I think erring on the side of caution, making sure you terminate maybe two weeks before planting to give yourself enough time for that cover crop to settle down and break down so it's not competing with that crop as it emerges. But the most critical time really is right around the time of planting and early emergence of our cash crops.

Chris Proctor:

And so I think if we can avoid competition from our cover crop at those times, that's what's really important ultimately, but a lot of this is learning. I mean, I've seen growers do some things that I would've thought were going to turn out to be failures and they've been really successful at it. But they usually start small, they kind of work into it. They figure out what works for them and the equipment that they have and how to be successful. So it's a little bit of trial and error for each field and each grower, so to say that there's a one size fits all, just wouldn't be true. So I think there's some good principles, and you're right in saying that we just need to be cautious that our cover crop doesn't become a weed itself and start competing with our cash crop. But I think we're getting better at how to manage that.

Sarah Hill:

All right. So you mentioned the importance of finding your goal, and if your goal is weed suppression, why is it important for cover crops to be established quickly, if that is what you're purposely using cover crops to do?

Chris Proctor:

Yeah, I think it goes back to the fact that we're asking cover crops to compete for those resources that the weeds might otherwise utilize. And so the faster we can establish the cover crop, the more competitive they can be against those weeds as the weeds begin to emerge. So if we can quickly establish cover crop and produce a biomass on those cover crops, then those cover crops are just going to be more competitive with the weeds as they emerge. And so I think that's just something that's important to pay attention to. And just as maybe an addition to that idea, knowing which weed species you have in your field, I think helps with that, the timing.

Chris Proctor:

So if you have a winter annual weed and it emerges in the fall, you might think differently about the timing of cover crop establishment and where you see the benefit versus an early emerging summer annual like a giant ragweed, for example, or a later emerging summer annual like a lot of our pigweeds. And so knowing a little bit about the biology of the weeds that are problematic in your field and when they emerge and when they're most competitive, it can help plan the timing and think through how to best utilize cover crops as well.

Sarah Hill:

All right. So can crop rotation of cash crops beyond just corn and soybeans also help with weed suppression to some extent?

Chris Proctor:

Well, I would say absolutely. So from a weed management perspective, I think tools in our toolbox is important. And I think anything we can do to disrupt weed cycles is always valuable. And so if you think about corn and soybeans, they're planted about the same time of the year, they're harvested about the same time of the year. So a lot of our systems have really selected for just a handful of weed species that tend to be really competitive in corn and soybeans. But if we were to add wheat, which I think is a great example, just to make the point, if you add that winter wheat to your rotation, now we're planting our crop in September, maybe October. And at the time when corn and soybeans are typically planted, if you think of what a winter wheat crop looks at that time of the year, mid April to the first part of May, it's actively growing, it's well established. It has a lot of soil cover at that time.

Chris Proctor:

And so a lot of the weeds that would compete with corn and soybean just aren't going to be competitive with wheat because the wheat is so well established at that part part of the season. And then harvest comes in July with wheat, so now you have opportunity to manage weeds with different tools, and you would be able to manage weeds at what would be mid season for corn and soybean. That's the end of the season for wheat. And so now you have some other opportunities there. So just thinking about in that sense, can you disrupt those weed cycles, and can you add something in that will allow you to manage weeds at different times of the year and using different tools? I think when we think about an integrated systems approach, that becomes a really helpful tool.

Sarah Hill:

Great. So where can our listeners go for more information about using cover crops in an integrated pest management programs?

Chris Proctor:

I know there's a lot of resources out there now. There's a couple that I'm familiar with. I've helped write a number of articles, and my colleagues have written a number of articles that we publish through the University of Nebraska crop watch website. And so that's one place that I would point folks to go look. The Midwest Cover Crop Council I think is a great resource, and they have a lot of material on their website. The Soil Health Institute, and they think a lot about cover cropping, cover crops. SARE organization. And I can never... We have so many acronyms, I'm not going to be able to tell you what it stands for off the top of my head right now, but the North-Central SARE has a lot of resources available about cover crops. And the IPM Center also has a lot of resources available. Those are just a few that come to mind that I've referenced before and I think are helpful.

Sarah Hill:

All right. Great. Well, thank you so much for joining us today, Chris.

Chris Proctor:

Absolutely. It was my pleasure. Appreciate you inviting me, Sarah.

Sarah Hill:

Yeah. You can hear more from Chris about cover crops and weed suppression during the National Cover Crop Summit, coming up on March 15th and 16th. Visit covercropstrategies.com to register for this online free virtual event.

Sarah Hill:

Once again, I want to thank our sponsor. MonTag precision metering equipment is helping producers achieve their yield goals while saving on seed and input costs. For establishing cover crops MonTag's family of seed platform equipment adapts to a variety of major brand delivery systems that will conserve seed and nutrients along with soil and water. Explore new options for your production and conservation goals with your MonTag dealer or on the MonTag manufacturing website. For more information about all things cover crops, visit us online at covercropstrategies.com.