Some Thoughts to Keep in Mind in Weeds Control Where Manures are Applied

March 8, 2022

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 - Thinking about adding manure into your fertilization scheme. One, I'm sure or at least one topic that should be on your mind is what weed seeds are coming along with that manure. And so Dr. Christy Sprague, this is actually part of two different presentations that she has recorded for us today. This one's specifically focusing on manure and weed. So we'll go ahead and hear what she has to say. - [Christy] Hello, this is Christy Sprague. And today I would like to talk to you about manure and weeds, and some of the things you should be considering. With the high prices of fertilizer that we're seeing, as well as some of the higher prices that we're seeing with a lot of the other crop inputs, one thing that many growers are considering is using manure and or compost as alternatives to synthetic fertilizers this year. While manure and compost can provide very good nutrients on several different fields, there are a few things that you may wanna consider when it comes to weeds. Sometimes with manure applications, we can end up bringing in new weed seeds, to fields that haven't been there previously, and some of those weeds can be harder to control. For example, if you had asked a farmer 50 years ago, if he would've seen velvetleaf in his fields, many of them would've said, nope, it's not a problem. We don't typically see it in Michigan. However, over time velvetleaf infestations have made it across the state. And a lot of that spread was due to manure applications. A couple other things that we've noticed more recently would be back about 10 years ago or so we started to see Palmer Amaranth coming into Michigan and this is another weed that we believe was spread mostly by manure applications, when Palmer Amaranth seed was brought up into different feed sources and fed to dairy cattle, as well as dairy and other beef cattle and was spread in various areas. So with that, we'd like to talk about some possible sources for some of these new weed infestations. Some of the things that you should consider, if you are gonna be applying manure and or compost to your fields, as far as weed management. As I mentioned before, Palmer Amaranth was one that we started to see more readily in the last 10 years. And again, we do believe that some of that was brought up in some of the cotton seed that was being fed to dairy animals. Another possible source could have been from hay that could have been brought in from outside of Michigan. And then we think of other possible sources of new weed infestations, and not necessarily focusing on Palmer Amaranth, but it could be any weed. It's just as animals are grazing, they tend to eat a lot of different types of plants. And some of those are weeds that could contain seed that could end up in your fields. Again, a lot of this is when weed seeds are consumed by animals, they generally will pass through the animal and could be spread with manure applications. There are other possible sources for new weed infestations, one possible source is through irrigation. A lot of times that generally happens with furrow or flood irrigation, which we don't see a lot of in Michigan, but that is one source that we can see as new weed infestations or new weed seed problem, new weed problems can become more prevalent in some different areas. Other potential sources can be from bin-run seed, where the seed isn't cleaned and we can have new infestations. If you harvest a weedy field, a lot of times you'll see that some of those weed seeds can actually end up in your grain tank. So if you're saving seed, whether it's a small grain like wheat or potentially soybeans, we can end up if we plant those seeds without having those cleaned, we can end up with some new weed infestations. And then obviously, probably one of the more ways that we spread new weed infestations is by equipment. In particularly combines are a really good source for spreading new weed infestations. Generally, if a combine hits one weed, and if you think of something like water hemp that can produce up to a million seeds, that seed can be spread out that combine and can go from one field to the next. So again, there are a lot of possible sources, but today I'd like to focus mostly on the newer applications. So one of the things, when I was doing some research, looking at what information I'd like to share with you today is there was a paper that was published in 1987 that really looked at the relative importance of sources of weed infestations, and they compared manure applications to irrigation to also bin-run seed. And one of the things that they found was that the manure applications definitely provided the potential for new or for more weed seeds to be put across the field than irrigation or bin-run seeds. So you can see here with manure, they calculated about 40 million seeds per acre could be added to that soil seed bank, irrigation only about 50 seeds per acre, and with bin-run seed about 74,000 seeds per acre. So again, probably manure applications are gonna probably be the biggest source. And again, it's not necessarily of weeds that we don't have, but it could be weeds that you currently have in your field. So that's one thing that could add to looking at trying to manage some of those different weed seeds. There are also a few different things that can happen when you look at where you get your manure from. So one of the questions I have here is, does manure from different farm animals impact weed seed distribution. So if you look at it, I've just picked, you know, five different common animals that you would see on a farm and what effect if they eat weed seeds and it passes through that animal, how much of that seed is actually there intact? Well, it's very interesting and doing some research on this, there was actually quite a bit of work done on this back in the 1930s. In 1934 Harmon and Keam published a paper that looked at the percent of recovered seeds from manure of calves, horses, sheep, hogs, and chickens. And you can see here there is quite a bit of variability and we'll kind of break these things up a little bit more as we go through this talk. So we're looking at some weeds that are very common to us today. For example, example, velvetleaf. You also see things like Pennsylvania smartweed and field bindweed on this list. There's also hoary cress which would be a mustard species, red sorrel, white sweet clover, and wild prairie rose, which obviously is probably weed that we don't have. But when we start thinking of some of the sizes of some of these different weeds that can impact how many are recovered and it could ultimately impact the viability of those different weed seeds. So for example, if we look at two of those, manure from two of those types of animals, from calves and hogs, basically what they found over all of the weed species, that 22 to 23% of those weed species of those different seven different species that we have there were recovered and were intact. And you can see by looking at these, some of these are very specific to the type of weed seed, but averaged over all the weed seeds. Basically you can see about a quarter of them made it through both of those types of animals. If we look at horses and sheep over the seven different weed species, basically 11 to 12% of those weed seeds were recovered. And one of the things that's very interesting is if you look at chickens, when chickens were fed these different weed seeds, you can see that basically because of the crop in poultry that really grinds up a lot of those weed seeds. And we don't really necessarily see that many weed seeds pass through chickens. On the rare occasion, something that has a very hard seed like velvetleaf. They did find 2% that they were able to recover. One other thing I wanted to point out here is with the different weed species. So again, field bindweed and Pennsylvania smartweed. If you think of those two weeds, they have fairly decent sized seeds compared to something like a pigweed seed or a clover seed. And generally they're fairly, have a harder seed coat than some of these other species. And if you look at both field bindweed and Pennsylvania smartweed, you can see anywhere from 7% recovered seed all the way up to 51% recovery. So you could, you know, pretty much see that, you know, if a, for example here, if a hog ate some field bindweed seed, you would expect 50% of that would be recovered. The one I really wanna point out here again, is velvetleaf, because that is a pretty common weed that we have. And you can see that velvetleaf can pass almost 50% percent through calves and remain intact. Horses and sheep a little bit less. And you can see about close to 40% with hogs. And again, with chickens, we didn't see, or they didn't see very many seeds that were remained intact, but they were able to find 2% recovery from chicken manure. But even though you recover the seeds, probably the biggest thing is what is the viability of those seeds? So they also examined what that weed seed viability was. So they basically looked at this and put it on a percent of viable seeds. So if you had fed, you know, a hundred seeds to calves and of velvetleaf seed, and you're recovered a certain amount, and I think we're close to 50%, 22% of those seeds would be viable. And what that really means is that 22% of those are gonna be an issue in your future fields. So whether it's that year or the following year, those velvetleaf are gonna be a problem in the upcoming years. So if we look at these, we can look at them a little bit closer. And what I did here is highlight anything that was above 10%. You can see that definitely with the calves and the hogs, as we saw more that pass through those types of animals, we also see more viability. We also see that hoary cress was pretty viable when it came out of horses and also white sweet clover. And again, I'd like to just kind of focus here on velvetleaf and kind of give you an example of what that actually might mean. So for example, with calves and hogs, again, around 20% viability, once those pass through some of those animals. So let's look at that as an example. So if we think about velvetleaf seed. Velvetleaf seed, if we look at a velvetleaf plant, they produce flowers that turn into capsules. And in each one of those seed capsule are several hundred seeds. And in general, if we think of a velvetleaf plant, they can produce anywhere from 2000 up to 9,000 seeds per plant. So we'll just say on average, about 5,500 seeds per plant, and you can see a close up picture of velvetleaf seed. It does have a harder seed coat, it's a little bit larger than many of the other weed seeds that we deal with. So if you look at that, and we look at the 20% viability that we would potentially see from both calf and hog manure, that would pretty much mean if a cow or a hog ate one whole entire velvetleaf plant. And they had 5,500 seeds in there per plant. What would come out out would be about over a thousand seeds that were viable, that could be a problem in the future. So it's just kind of one of those things to keep in mind. And as I mentioned before, one that really has stuck out with us over the last 10 years or so was kind of the introduction of Palmer Amaranth. And again, this is a weed that was pretty predominant down south. And then we believe, you know, in different areas of state, as we started seeing this weed appear a lot of times, one of the things that was very common to those fields where we first saw them was that manure had been applied. And as we started looking back, some of that really had to do with what that seed source came from some of the feed that was fed to some of the animals. So here's just an example of what can happen. And again, as one of these plants can produce several hundreds of thousands of seed, that if one or two plants are able to make it through and are not controlled and produce seed, as we go through with different operations, particularly combines, we do spread that seed throughout that field and into other fields. So let's look at Palmer Amaranth seed as an example. Again that's a very small, small pigweed seed. And in general, there has been work looking at the seed viability of some of the different Amaranthus seed as they go through different animals. So for example, looking at a dairy cow, basically if a dairy cow was to eat Palmer Amaranth or have feed in it that had Palmer Amaranth seed in it, 27% of that seed would make it through that cow and be viable. So again, there's, you know, if we're producing a half million to a million seeds and let's say the cow ingests that, you can see that there's quite a bit that's gonna come out that's gonna be viable. There's also been some work that's looked at waterfowl, and we'll just use that as an example, and generally much lower viability, but they can still pass viable seeds. So in this case with, with ducks, they found that three and a half percent of seed that was fed to ducks remained viable as it passed out of that animal. One way we can help reduce the amount of seed that would actually go into an animal's feed, like for example, dairy cattle or beef cattle or hogs or so forth, is by ensiling some of the different feed sources, because it does reduce viability, seed viability. So for example, here's hay, and you can see an alfalfa hay with Palmer Amaranth growing in it. And if that alfalfa hay leaves was ensiled, basically it would reduce, only 59% would be viable after one month, if you waited two months, 13% would be viable. The longer that that ensiling process takes place, the more viability that we would lose from that weed seed. And again, this is with Palmer Amaranth and if we look at corn silage, kind of looking at the same example, we would see a little bit more reduction in viability. So only 40% viable after one month and less than 13% viable after two months. So again, you know, this is one way that we can help reduce the viability of the seed that the animal is eating, and that does work well. The other way that we can reduce the viability of weed seeds, particularly in manure, is by composting and really what we've or what's been known for a while is that composting can reduce the viability of weed seed. It basically destroys it, but the key thing is making sure that the temperatures need to be above 140 degrees Fahrenheit. To be safe, 160 degrees always works better, but those composting piles really do need to keep that heat level high. And that's why it's important to make sure that those composting piles are turned and also moisture can have an effect on that, but it does reduce viable weed seeds. And here is a study that was published in 2000, looking at composting effects on weed seed viability. And they looked at some very common weed seeds that we have today. Things like common cocklebur, foxtail species, morning glory, pigweed species. So that could include Palmer Amaranth, that could include water hemp. It could include redroot pigweed, or Powell Amaranth, shattercane, and then also velvetleaf. And they looked at composting dairy manure, and looked at different times. And I'm just going to show you kind of one of their starting times after one turn versus after the amount of turns that they did in five months. And this is looking at a ten inch depth of the compost windrow. They also looked at deeper into that windrow, but I'm just gonna show you kind of that upper level. So you can see that after one turn with dairy manure, you could still see that many of these seeds are very, are still highly viable. For example, 24% of cocklebur was still viable. 77% of pigweed was still viable. So that would be something like a Palmer Amaranth again, and 11% of velvetleaf. But after five months of this good composting, basically we saw that there was zero viability left and that in this dairy manure actually was 12 different turns of that compost. And the only thing that remained viable was velvetleaf. And that didn't change from one to 12. So again, with that thicker seed coat, it is, that's one of those ones that are extremely tough to reduce that viability. When we look at beef feed lot manure, they looked at both dry and wet manure and with the wet, that would be greater than 30%. They kept it very moist. And you can see here that there were some big differences. So again, with the dairy manure, pretty much all viability was lost except for with velvetleaf after that five months, and with the beef lot manure, you could see that after the five months where there was seven turns, they did reduce complete viability of all those weed seeds, including velvetleaf, and with the wet manure, with that moisture in there, that also sped up the reduction of viability of those seeds. And that was basically zero. So let's look at pigweed and velvetleaf, because again, these are ones that are completely different, but have different effects on some of our fields. So for example, with the pigweeds, which again, would include things like water hemp, Palmer Amaranth, a lot of different ones. You can see that if we give it that full time of composting, we can see that reduction in viability happen quite well. With velvetleaf, the biggest where we didn't see much, where they didn't see much difference was with the dairy manure. So a lot of times some of the manure that we have that goes out on fields is liquid manure. The one thing that even though that it's under anaerobic conditions, it does not necessarily reduce weed seed viability. It may have some weeds, but it doesn't have Amaranthus species. And there was a study that was conducted in 2003 to look at that. There's also been some work that has looked at some digesters and they haven't seen that it's reduced any of the pigweed viability either. So if we're spreading this, what are some of the things we need to consider? So when we look at using manure, let's think about what are some of the things we need to think about to make sure that we don't end up with a huge weed problem? Well, one of the things to consider is to know where the source of that manure is from, if you know where the source is, you can pretty much ask others that have taken manure from that place before. One other thing that you could do is, you know, if you live close to that area, you may know what the weed problems are in some of those fields where that manure from that source has been applied previously. So it's really thinking about kind of knowing where your manure comes from, what might be some of the potential weed problems that might occur in some of your fields. I guess if the source of that information is unknown and you don't know where that manure is coming from, or potentially compost, as I said, compost really reduces the viability of the weed seed, but you could still get a few that make it through, make sure to have a comprehensive weed management plan in place. And I think that's one of the, probably the most important things. So one thing I'd like to think about when I think about comprehensive weed management plans, you know, in general, a lot of times we've relied very heavily on glyphosate to control many weeds that we have out there, but we do have several weeds that are resistant to glyphosate and to several other herbicides. So I think it's always important to know what those weeds are. So in Michigan, we have several different weed species, and I'll just mention the ones that are resistant to glyphosate, 'cause those are generally one of the, some of the ones that we tend to have more problems with. And the other thing is thinking about this year, where input prices are quite a bit more expensive as well as product being a lot more limited. There may be some instances where you won't have that glyphosate to use to help control some of those weed species. So as we look at this list, you can see things like horseweed, Palmer Amaranth, water hemp, common ragweed, giant ragweed, that have all been found resistant to glyphosate in different areas of the state. And then you can see some of the other ones, probably one of the other things I'd like to bring into your attention is the triazine or atrazine resistance. We do still have a lot of those weeds that that are resistant and then the newer ones with the PPO inhibitors, which would be things like Flexstar and Cobra, post emergent, so things like common ragweed, water hemp and Palmer Amaranth. Another thing is many of these weeds species have multiple resistance issues. And that can be a big problem. In particular, as I mentioned before, Palmer Amaranth is one of those ones that we saw potentially spread with manure and knowing that we've had glyphosate and ALS resistance in that particular population that came in to Michigan, as well as we're starting to see some resistance to the group 14 or PPO inhibitors, as well as atrazine, which can be a problem when we're trying to manage it in corn. And we're seeing some of these different resistance issues, because again, with horseweed and giant ragweed, common ragweed, water hemp, most of those populations that we see that are resistant have both glyphosate and ALS and in some cases they have some additional ones like the PPL resistance. So considering that there might be some herbicide resistant weeds out there, it's really important to thinking about what you're gonna do from a weed management standpoint is to start with a clean seed bed and that can be done by tillage or an effective burn down herbicide. And there's a lot different choices that are out there, both in corn and soybeans. And a lot of that information can be found in the weed guide. Also again, thinking about a comprehensive weed program, it's always good to start out with a good soil-applied product or pre-emergence product. And we've got a lot of different options. And just wanted to mention again, we've got those charts and the weed guide tables 1A and 2A for both corn and soybeans that list all the different soil-applied products and what weeds they control. So if you think you might have spread something like Palmer Amaranth, you can look and see what are some of the options for good control. The next thing to consider is making sure that you scout prior to that post herbicide application. So those soil applied herbicides should have reduced the number of weeds that you're gonna have to manage post emergence. But it's also important to know what weeds are out there and remember to do that when they're small, and then to make very timely post applications. So for example, if you go out there and you're planning on making a post application, make sure you know what weeds are out there and what stages they're at. Here's a picture. This is probably a little bit further along than what you would want, but again, making sure that you identified what the weeds are that need to be controlled. And again, we've got a lot of different options in both corn and soybeans and we have those tables listed in the weed control guide, both tables 1B and 2B. And then finally after you make those post applications, make sure you go out there again and take a look and see how well those post herbicides worked. In some cases you may need may need to come back with another post emergence herbicide application. If the first application didn't work based on what that herbicide was, you may need to switch that up. So with that, I'd like to just kind of go through a few take home messages while thinking about manure and weed seeds, remember manure and compost are excellent nutrient sources and could be an option for replacing some of the more limited or higher fertilizer costs that we might see this year. Weeds can also be transported and spread by manure as well as several other things. One thing that we've went over is that both weed species and animal type can influence the viability of weed seeds in manure. Another thing that we mentioned is that really ensiling can help reduce weed seed viability. And that's really prior to feeding, you know, some of, whether it's cattle or hogs or any thing. The other thing to think about is composting manure can reduce weed seed viability and again, the temperature and moisture are really important. And then probably the biggest thing from a weed scientist standpoint is be prepared with a comprehensive weed management plan, you know, consider the potential that there might be some herbicide resistant weeds out there. Do you have a good plan in place, both in your corn and beans or whatever crop you're going to, to help manage some of these higher weed populations that we might see with manure applications, or some of the newer weed issues potentially. And then again, probably the most important thing is scouting, making sure that you scout prior to and after a post herbicide application is gonna be critical. You wanna make sure that any new weeds that are out there that you're managing those so that they don't become a huge problem in the future. So with that, I just wanna mention that we do have our website,, or you can use the other web link there. And on the website is the 2022 MSU Weed Control Guide for Field Crops. And that should provide you with some good options for control of potentially some of the weeds that might be coming in. And again, it's, this is not a talk to scare you from using manure or compost, but just to make you aware of what potentially could be some new problems that you may run into. And if you have a plan in place, it shouldn't be a problem. So thank you. And I hope you guys enjoy the rest of your day.

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