Herbicide Carryover, Resistance Management, and Cover Crop Termination: What You Need to Know

0:07 I appreciate the opportunity to be here. It was a rather daunting task whenever he told me what he wanted me to talk about. I had to go through and look at I think what are 96 different cover crop species that he mentioned, and then I tried to think about every rotation between corn, soybeans, sunflowers, cotton, wheat, and then work out all the interactions between all of those. So we should be done sometime next week if that's all right with y'all. If not, I might shorten it up just a little bit.

0:42 I'm just going to talk basically about herbicide considerations on what you need to think about for cover crops, not anything that you're going to do really specific. There are such a wide range of potential options that it's really hard to address all of them.

0:57 The main things we want to consider: one of course is what about carryover from our primary crop, whatever herbicides we happen to use in our main cash crop or whatever. How will that affect what cover crop options that we've got? Then we've got weed management within our cover crop. Just because it's a cover, hopefully we could get by with not having any weed management issues, but in all likelihood, I like to treat things as a crop that I'm trying to grow. I'm farming that cover crop. I want it to be successful. So if there's weed management that I have to do within that cover crop, that's something that we need to consider.

1:35 Then I've usually got to terminate that cover crop. What considerations do I have about how I'm going to kill that cover crop so that I can go back in and plant that cash crop at the right time? And then if anything that I use in that cover crop, I happen to have carryover back to my primary cash crop, whatever is in that rotation, I want to consider.

1:59 To be able to take that into consideration, I really appreciate a couple of speakers yesterday talking about planning on your herbicide rotations and what your crops need to be, where you're going to go for 3 to 5 years down the road so you kind of know which direction that you're going to be. So I think that's a really important thing.

2:17 As a disclaimer, I am going to mention some different products out of specific labels. I am not recommending any of these things. You know, anytime you're using a herbicide for any purpose, you need to look at what weeds you're trying to control, what crops you're trying to control those weeds for, and then what your next rotation is going to be. So these are just for example only.

2:44 So first, let's look at carryover from your primary crop. You know, this is a herbicide that is used and has residual activity potentially on your cover crop or crops. You'll notice a theme all the way through this: the primary source of information on where what that might be able to be used for or what herbicide carryover issues you're going to have is going to come out of that herbicide label.

3:14 Almost every herbicide label is going to have a rotational crops section with rates, months depending on what rate, and then a list of crops that is legal to rotate to. What chemical companies have done is they've gone out and done testing to see how long their herbicides last in the soil and how long it's safe to wait to come back and plant those different crops. If the cover crops that you're trying to grow happen to be listed within that rotational list that's included in the label, you're free and clear. That's the easy way to go because you're able to just pick off of that list.

3:57 That and then follow whatever recommendations are on that label. But there's such a wide range of different cover crops planted, odds are it's not going to be on that list. So one of the things that I do after that is you look at this list and try and pick out a crop. You know, whatever if there's something fairly similar in the same family or even Genesis is the cover crop that you're trying to plant, you're kind of on your own at this point in time. Because if the crops that you're planning are not specifically listed, then you don't have any label protection if the herbicide does happen to kill that cover crop and causes you to have a failure. You have no protection if your cover crop is not specifically listed.

4:46 The other thing to do if your cover crop is not listed as the rotational crop is look at the weeds that it says that it will control. Every herbicide pretty much should have a list of weeds that it's going to control. What they recommend, usually what rate is going to be, you want to look at ones that are going to get pre-emergence or a residual control. If it's strictly post control, then it probably wouldn't be an issue. But if your cover crop is fairly similar to the crops that are listed on the herbicide label, then you can kind of count on you may have some issues. For instance, on this label, if you look over here, wherever the Brassica species, obviously if that's got pre-emerge activity on the brassicas, there's a pretty good shot that if you were to go in and use mustards or whatnot inside your cover crop, you would have a greater risk of failure.

5:53 Next we want to look at, consider weed management and what's inside your cover crop if you.

6:00 You happen to have to manage weeds if there's something that you need to do for a simple crop or for a single crop. If you're only using one and you're not using a diverse mix, it's a relatively easy approach to it. You just look on the herbicide label if your cover crop is listed, you're going to be ok on that. You just use it and follow up all the label instructions.

6:32 If you're using a multi-species, as we hear a lot about, then things get really challenging, particularly when you throw in legumes and things like that. It's hard to find a herbicide that's going to be labeled for everything that you might consider putting in a lagoon. One of those 25 species blends would scare me to death trying to come up with a good herbicide program to try and use within that.

7:00 What you want to do then is look, obviously if in the multi-species if they're all listed on that herbicide label, then you just got to be able to follow the instructions for each one of those. But you have to follow the instructions for each one of the crops included. One of the things to be considered is that different species have different tolerance levels, so there's the potential that you would have to use a different rate for one as there would be to another. If you follow those label restrictions for all of the crops, you should be alright.

7:39 Again we get into if it's not on that herbicide list. I apologize, it actually got the wrong table on this one. There's a table of weeds controlled list that should have gone on this slide. If your cover crop again is similar to one of the things that is listed on the weeds controlled, then there's a pretty good shot that if that you would.

8:02 Would have problems with planning a similar species. Likewise, if there's similar crops to what that cover crop is, you may be able to get by with that. Like I said, the weeds controlled. If you look at that list, if your cover crop is included or something similar to that, you've got a good chance of problems and failure.

8:28 One of the big things to consider is grazing restrictions with these cover crops. If your cover crop is not on that label listed and a grazing tolerance provided, then you cannot legally graze that cover crop. That means there is no tolerance set with the EPA that handles and regulates herbicides or all pesticides for that matter.

9:01 Now the grazing restrictions that you're going to see, they're going to look something like this. Ideally in the perfect world it would be no grazing restriction. I can go out there and spray and be able to go right back into that field without a problem. More likely, most things you're going to see are going to have a certain days after application. Of course, this works the same thing for any type of crop that you might be grazing. You need to follow this. This allows enough of that herbicide to break down within the plant so that there you don't have any potential tolerance issues.

9:41 Another thing would be there's also often grazing restrictions based on whether animals are lactating or not, even withdrawal periods if they're going to slaughter. You need to be able to watch those grades and restrictions or whatever you do. And then a lot of things that may or may not be labeled that you might want to be used in a cover crop that's a green manure crop.

10:01 You can get away with it but a lot of these, if the chemical company has not spent the money to develop that grazing restriction or grazing tolerance, then you won't be able to. They would not have put it on the label. Doesn't necessarily mean it's bad, it just means a chemical company didn't want to spend the millions and millions of dollars it takes to put that little sentence on the label. So if that's the case, then no grazing would be allowed period.

10:29 Next foot deal is that we talked about is termination of your cover crop. It typically is glyphosate or Roundup. Has gotten so much cheaper. Back when it was, you know, I can remember paying $90 a gallon for it. We didn't use it nearly as freely as we do now. When I go out there and I can spray a quart for about four bucks, you know, so it's something that we've gotten so used to using. We created ourselves a lot of problems, and particularly when we're looking at diverse cover crops where you've got broad leaves and grasses all mixed together that we may want to terminate using something that's a broad-spectrum herbicide.

11:19 That we'd be really interested in or don't like to do, especially if it's as cheap as glyphosate is. But the problem we see right here, all of the use that we've had, and very particularly with Roundup Ready crops and the reduction in price of glyphosate, we've overused glyphosate in a pretty bad way. What we've done is we've gone out there and selected for glyphosate resistant ecotypes within different species. Mayweed is probably in this picture, probably one of the most common. It was one of the early ones, but glyphosate now we've selected for resistant populations. I think it's like 68 different weed species.

12:03 Was the last count that I heard and once you have glyphosate resistance that's a dominant trait so you will basically always have glyphosate resistance within that population. So what we want to do is we want to try and look at some other things as a resistance management tool.

12:22 Weed Science Society of America basically divided all of our herbicide families into different site of action classification numbers and the only way that we're really going to prevent herbicide resistance from beginning or really getting out of hand is if we do something to remove that constant selection pressure off of one of these site of actions.

12:49 Roundup if you look on it that's the active glyphosate is the active ingredient it's a group 9 so you know that that's the mode of action on it. If you change from one glyphosate to another glyphosate to another glyphosate you're not doing anything different.

13:11 Were to change to something else that had a group nine if there was another one out there glyphosate is really the only one in that side of action family that doesn't do anything. Changing brand names whatnot doesn't do anything to limit or reduce development of herbicide resistance.

13:28 If we're trying to go with broad-spectrum if you're wanting to use a single control method for a wide range of broad leaves and grasses and whatnot then we need to go with a couple of one of the other broad-spectrum or non-selective type of herbicides. One of them is glufosinate active ingredient Liberty if you notice it's a group 10 so it's a different site of action within that plant. Now there are Liberty link or glufosinate tolerant plants crop plants that are out there now so we're trying to not make the same mistakes with glufosinate that we did with glyphosate. They sound pretty.

16:30 For some sort of weed control within our, or cover crops or to terminate those cover crops if you happen to use something other than one of those non-selective herbicides that did have residual, I'll make sure that's not going to carry over back to your primary crop. Again, same thing—the herbicide label is our friend. It's got the information that we're going to need to have. You will want to make sure you know for certain that your primary crop that you're planning back to is listed within that rotation. That's for two purposes: one is product safety going back to that crop, so you know you're not going to damage your stand on your primary crop. Nobody wants to hurt their yields on their main cash crop. The other thing is some herbicides can again have a sole residual carryover that can be picked up that might result in illegal residues in the following primary crop.

17:34 So you want to make sure that whatever you're doing, whatever herbicides you use, whatever is in that rotation that you've planned out years in advance, you know that you've got that covered. If the primary crop is not listed as a rotational crop, then you're kind of at risk. If there did happen to ever come up with something where there were illegal residues left over from that previous crop or from the cover crop herbicide, then you might be at risk of that. But the primary risk is if your primary crop is not listed as a rotational crop—the risk that that residual is going to cause either stand damage or yield reduction in your primary cash crop. So if you can hopefully stay with something that's listed on the rotational, then you're in good shape. That's probably the main thing.

18:41 Don't know anything or if you're unsure, we want to be sure as you can be. The next step is probably to go with a bioassay of your feet. There's a number of different ways to do that. A lot of herbicide labels will actually have instruction on how to conduct the bioassay. They're usually doing it out in the fields where your crop is actually growing. I'm not a big fan of that because typically if you're going back with my primary crop that I want, then I want to see whether it works. I need to know that before earlier than it takes. If I'm going to try and plant that crop actually in the field, sometimes you can go with a more sensitive crop that may pick that up.

19:35 But if you do the field bioassay, it's the most accurate you can. Plant strips across that field of something more very similar or whatever your primary crop is going to be. If it comes up in a gross, then you know for certain you're in good shape. What I've tended to use more often has been a container bioassay where we actually go in and collect soil from multiple areas within the field that's been treated as well as collect soil that has not been treated and then plant something inside where I can control the environment and I know whether it's. Typically you'll take like the top two inches of soil, put it in one of these containers, plant it to a sensitive seed, put it on your windowsill or whatnot. That way you can find out without having to wait until the weather is appropriate for actually going back to test with your primary crop.

20:29 There's a number of different publications out there on how to do a bioassay. I really like this one from Nebraska. You can find the link to it or you can just search bioassay libguide.

20:43 Come up with that. It's a very good source. One of the things that I can't stress enough is always read and follow those label directions. Herbicide labels, in fact all pesticide labels, are governed by the US EPA and they carry with them the authority of law. Violation of any aspect on a pesticide label is a violation of federal law. Now you're not likely to get thrown in jail, probably not, but you're not likely to go to jail or anything like that.

21:22 The risk of violating the label beyond potential damage to your own crops is the risk of having your crops actually condemned. I know that's happened more than once in Texas in particular. There's a product herbicide called MSMA, which is an old herbicide, but it's one that the Texas Department of Ag really takes a big interest in. MSMA contains arsenic in it. People have used it in lawns and it was used in cotton fields for years. It controls sandbur really well, so a lot of horse hay people want to use that. I have seen horse hay loads get tested and condemned, which means the Department of Ag says that you, that's no longer saleable and now has to be disposed of as toxic waste. So it's a really expensive disposal. You lose your crop. It can be a really bad thing.

22:25 So I can't stress enough to read and read and follow that label and it's going to help you with your herbicide management with cover crops or anything else. Summary of what I've got to say, you'll rot behind. I'm going to finish early, going to make up the key. The herbicide label is going to be the primary source of information on both the spectrum of activity and what its carryover potentials are. I know lots of people don't like to read them. They've got lots of stuff and legalese sounding.

23:00 Words in them and small print. This is our number one source of information, not just for cover crops or whatnot. You need to do this for any pesticide that you're going to apply to make sure that you use it safely and effectively. The bioassay, if you've got any questions and you want to make sure, the bioassay is your best estimate for site-specific estimates of carryover risk. There's really not a better way that you can know for sure because even though something may be listed on those rotational labels and whatnot, labels are meant to cover a wide range and both plants and herbicides don't always read the book to know what they're supposed to do. Bioassay will tell you pretty much for sure.

23:49 Remember to consider your resistance management. That's not just what didn't cover crops or whatnot, that's within any herbicide. Our herbicides are a tool. I'm a spray guy. I like to spray weeds. I freely admit that Jeff Goodwin harasses me about it on a regular basis, but it's as much as I like to spray weeds, a lot of time I want to make sure that I use my herbicides in the manner that they need to be used. You know, utilize your integrated pest management principles. You know, spray according to economic thresholds, preventive measures. You know, use your herbicides well and rotate modes of action whenever you can.

24:35 The important thing is by rotating those modes of action, what we do is we maintain that tool in our toolbox. You know, we sometimes may spend more money in one year than we would necessarily like, but I can guarantee you the guys that are now running up hundred-dollar hoe bills and trying to control life-site resistant Palmer amaranth wished that years ago they would have decided to rotate their modes of action and being able to maintain glyphosate is infected material on it.