S1E2: 2024 Peanut Weed Update
Join us today as we hear from Weed Specialist Mike Marshall as he discusses topics ranging from resistant annual Ryegrass, Reviton herbicide, and managing Texas Panicum.
Date: Feb 22, 2024
Location: Allendale Extension Office
Twitter - @ClemsonWeedSci
Production Credits:
Introduction: Hannah Mikell
Producer: Kevin Royal
Editor: Kayla Peters
Technical: Trey McAlhany
Music Composer: R.M Davis
Special Thanks:
Transcript:
[Hannah Mikell]
Welcome to today's episode of Cultivate Ag, where we will delve into the latest developments in agricultural research and practices. In this talk, Dr. Mike Marshall, our Weed Specialist, will cover a range of agricultural topics, such as tackling resistant ryegrass and exploring innovative herbicides like Reviton, along with insights on managing your Texas panicum.
Stay tuned for valuable insights that could revolutionize your approach to weed management. Thanks for having me here today. I'll talk a little bit about some of the work we've been doing at the station in weeds and peanuts.
[Mike Marshall]
First, I want to talk about ryegrass. That's something we've been working on with resistance. Updates on that, working on it up in the upstate.
I want to touch a little bit about a new burndown product that we're trying to get a 24C label in peanuts for. It's called Reviton. It shows some pictures of some work I did.
It was in soybeans and cotton. We're trying to get it registered in peanuts for burndown as an additional option for you. A few slides about the resistance survey.
I had a grad student who finished it up last year. I want to show a few results from that that are applicable for peanut herbicides. And finally, another project we're working on, looking at Texas panicum.
It's a weed that I get a lot of questions about, and we seem to be having more problems with Texas panicum through the years here. First, I want to talk about the ryegrass. This is a winter annual.
I've been getting some calls. Burndown problems with controlling this. Does anybody in this area have problems with it, with burndown, with glyphosate?
There's some other areas in the state we collected samples from. This is a field we sprayed a good burndown program, Roundup, Leadoff, and 2,4-D. This was in March.
We came back. It looked like things were working there in March when they sprayed. Came back about two and a half weeks later and all that stuff that looked like it was dying, it greened back up and started growing again.
I did a little down and dirty, really quick, two-week project up there with it. We cordoned off an area of that field, and I sprayed Roundup, just Roundup. Check up there, you don't really see a lot of difference, except when you get up to the four quart rate of Roundup.
You start to see more dead plants in amongst that picture there, but you still see quite a few live plants there. That's a good indication that we've got some resistance problems. This population, along with about ten other populations that we've been working on, we took them to the greenhouse.
This was actually last fall. Just to confirm what level these populations have resistance, this is a glyphosate screen, and this is sampling of five populations, and you can see some of them from 0 to 4x roundup rate, and you can see some of them, populations are still fairly sensitive. Some are controlled at the 1x rate, while others, you see green plants there at the 4x.
I've been working on these populations this past winter, trying to get some dose response curves generated for these, but obviously we have resistance that were soon to be confirmed in ryegrass, and that would be three resistances we have for ryegrass. We already have ALS, we already have ACCAs, and now glyphosate. So, what can we do if glyphosate doesn't work?
What are the next options for us? We looked at some residual, other states have published work on residual herbicides, and I got some up there, Valor, Zidua, Metribuzin, and Dual Magnum, as a way to spray these in the fall, before the ryegrass emerges, or germinates, and this would control those flushes through the winter. The fall is typically whenever you have the biggest flush of ryegrass, you have some in spring, February about right now, you might have some more, but the majority of it's in the fall.
So we looked at this, the thing that I wanted to point out on this slide was Valor. Valor does have some post-emergent activity on ryegrass. If you're a little bit late getting it out in the fall, it would control that seedling ryegrass and provide residual at the same time.
The others obviously work too, but they don't have that post-emergent activity. But they did work if you got it out early enough, before the ryegrass emerged, and that's 90 days. We also looked at cover crop, cereal rye, we wanted to look at, this project, we wanted to look at how Valor, how these residuals would interact with the cover crop, and we did see some injury with Valor and Metribuzin on rye.
Just the cover crop by itself, in the middle there, did control it, shaded it out, because cereal rye comes up very fast and shades out what's there. So, we could not see any ryegrass coming up in just the cover crop plot. So, I mentioned some strategies here for ryegrass management, I mentioned the resistances we have now in South Carolina there.
Obviously monitor your populations for escape, for control failures. I know this time of year when we have cold nights, it takes Roundup a long time, if we're burning down for corn, I know it's a little early for peanut, but when it's cold out, it takes a long time for a product like Roundup to work on some weed. So, monitor that.
We're continuing to work with the fall residuals, I think that's going to be our backup, I guess, for ryegrass. So, if you're going into a field where you know you have ryegrass in the cover crops, that would be a good option too. That's it on ryegrass.
Let's talk about the Reviton product. Again, you know, we often have trouble with a lot of mustards, primrose, some other difficult to control weeds with our burndown programs. And I just listed a few here, programs that are common, you know, I mentioned 2,4-D Roundup, and then you add some residuals like Leadoff or Valor, or use some like a burn type herbicide, this glyphosate with Sharpen or Goal, and the Reviton.
Those are all contact herbicides, so they will help some of these larger plants like you see there, that mustard that's flowering. Real quick here, I mentioned we applied for 24C, that's the special use label for South Carolina. It's already registered for corn and soybeans and cotton.
I think when we get it, hopefully soon, it'll be seven days from application to planting for peanuts. Of course, we won't know that until it goes through the EPA and the registration process on the 24C. But I want to show you some pictures of some plots that we did.
So, the check is on the left. On the right, so, this is Reviton at one ounce. The flag is in the center of the plot, it's a 13-foot wide plot.
So, this is Reviton and glyphosate. You can see that it's at the one ounce rate. You can see some primrose there at the bottom of the picture.
It's not as controlled as we'd like it to be, as we had 2,4-D in it. This is Reviton with 2,4-D. 2,4-D helped us with the bigger broadleaf weeds at the one ounce rate.
And the two ounce rate, really, I think that's a better amount to apply because you can see the difference in primrose and other stuff. You see there's a lone oak plant out there. It seemed to survive it really well, but we typically don't have that as a burndown weed.
But you can see the others there. Some ryegrass in there too is controlled pretty well. I always compare that to Leadoff and glyphosate.
Leadoff's a pretty popular herbicide program in the state. It's a residual, so it did fairly well compared to Reviton, but just like I said, another option for ryegrass and stuff because these populations of ryegrass in this field are all sensitive so far. So, don't take that one to the bank.
Cross all your fields thinking it might work. Glyphosate alone, this glyphosate program might still work. Just keep an eye on that.
Anyway, I wanted to show you those products. Keep it on your radar. And finally, glyphosate and 2,4-D.
Let me talk a little bit about the survey. I had a student do this for his master's. We did a big survey across the state.
And I'm only going to focus on the blue rows here. Those are the herbicide families that we use in peanuts. PPO inhibitor, ALS inhibitor, and Dual Magnum, a group 15 herbicide.
I just want to show you some of the result from those three groups. This is Dual Magnum. So, we use Dual Magnum quite a bit.
Group 15 is Zidua, Warrant, Outlook, they all belong to the same family. So, this Dual and others are a big part of, especially in peanuts where we use a lot of residuals in our production to control weeds, control Palmer. This is Palmer amaranth.
So, this just indicates that on the zero side was susceptible, completely controlled. Over on the right side of the graph, that's where we had 91 to 100 per cent emergence of that population. So, as you can see, we're starting to trend, don't mean to scare everybody, but we're starting to trend to see some populations of Palmer amaranth that are surviving a pre-emergent application of Dual.
You know, obviously we have these population locations noted and we're going to keep an eye on those. Other states, North Carolina, Georgia, and others have confirmed populations that are not resistant yet but are starting to show reduced sensitivity to our group 15s. This kind of little map of the heat maps in the red is considered on the resistant side, I would say greater than 70 or 80 per cent emergent.
So, you can see it's pretty well spread across the state, the red dots there. ALS herbicide in Palmer amaranth - ALS was first documented in the late 90s, 97. We still have a good amount of resistance out there, but there's more susceptibility there than I anticipated.
I thought we'd have most of it over on the resistant side. Greater than 71 per cent of the populations would be over there. That was unexpected, but there's some places in the state where ALS herbicides still work.
Another map here again shows the, look at the red dots there, those are the ones where we found populations that were on the high side of the resistant scale, which is expected. Some places were more red than others, but you still saw a lot of green there, susceptible across the state. And this is Reflex.
So, we use Valor. We use several other PPO inhibitors in peanuts, so we don't use Reflex that often. Good news is that all but like eight populations were controlled 100 per cent, so we're going to keep looking at that.
But again, that's a very low level there. Only 11 per cent of the populations we had some survivors. So, we're going to keep looking at that.
I was kind of relieved to see that that herbicide family is still working for us, given that in other crops, we use Reflex a lot. All right, moving on to Texas panicum. Again, I mentioned that we're doing a project.
I have a new student working on this project, and I just wanted to talk about Texas panicum as a large seeded grass. And the group 15 herbicides, like Dual, I mentioned, and others, don't work on this herb. Well, they suppress it for a time.
Prowl H2O, the group 3 herbicides are the ones that work much better on this grass, but we can only use Prowl at planting, we can't use it any other time of the season. Looking at our residual programs in peanut, we often see escapes or late mid-season, late season emergence of Texas panicum. Clethodim or SELECT is usually the go-to herbicide for that.
This project, we looked at five different weed sizes. Out of those sizes, we had three sequential applications. One application of Clethodim, the first three sizes, there'll be two to four, four to six, six to eight, and then the greater than 12 up to the bigger sizes, we did sequential applications.
And the second study, we looked at different adjuvants. Crop oil concentrate is the recommended adjuvant for Clethodim, so we included that, and we also included AMS as supplementary adjuvant to see if that helped us in controlling Texas panicum. This is the data.
What I want you to take from this slide here, as the weed size gets bigger, our control decreases. And you can see that as the bars get shorter and shorter, as the Texas panicum gets to the eight to 12-inch size to the greater than 12-inch size, which is expected. The Clethodim label specifies four to six is the optimum height or less.
It's kind of expected. If you don't see that Texas panicum until it's a larger plant and it's tillered and all that stuff, it's going to be much more difficult to control based on this data. However, if you look at the sequential applications, the last three groups of bars there, the six to eight with two shots of Clethodim, we're able to get that control near almost a hundred percent.
But again, as we get larger, that efficacy declines even with the sequential application. So just keep that in mind that you want to try to spray it as small as possible. That's true with any weed, especially post emergent.
And there's some pictures here from last year. And so this is the four to six. You can't see it very well in the picture, but the growing point is pretty much dead in that plant.
It just takes some time for the rest of the plant to die. But compare that to the big Texas panicum, we still got a lot of green tillers that will survive that application and keep producing seed. That's a comparison between the two sizes.
The adjuvant study, we looked at different adjuvant combinations. Crop oil is recommended, the COC and methylated seed oil is also on the label as a potential additive. NIS is not.
It's not recommended. But as you look at methylated seed oil and crop oil, we didn't see with crop oil, we didn't see a benefit to adding the AMS, but with methylated seed oil, we did see a bump with the AMS. So, if you choose to use, if you want to use a methylated seed oil, it would get you almost to the same level as crop oil.
But this data shows that crop oil alone still provides the best control for Texas panicum post emergent. Also throw in that weed size there, so four to six, its control is higher than at the eight to twelve. Regardless of the adjuvant we use, we still see a decline as weed size.
Looking at, obviously I mentioned before, residuals that we use in peanuts are the Dual Magnums, residuals, et cetera, suppress Texas panicum for a time, but we don't have season long control of Texas panicum using those residuals. So, we developed a project where we wanted to look at residuals and cover crop in combination. So, what we did is we planted a fall cover crop of cereal rye and oats, and then we had no cover crop.
And then we had these herbicide programs and we had a typical application timing, about two weeks, a month, two months, 75 days for the application timings. And I'll show you, there's a lot on the slide here, but there's, there's just some different programs that we often use in peanuts. I think a lot of people use two shots of clethodim during the season.
And that's what I have on the three and four there. And the post two is just different at 30 days. So, we have programs with Cadre and without Cadre.
Some folks don't want to use Cadre because of the rotation concerns with cotton. So, I put those in there as a, I don't want to use Cadre treatment. Here's some of the results.
So, this is about two weeks after the 30-day treatment. You can see actually where we had Cadre, we did tend to see better Texas panicum control than where we just had the other residuals like Dual and Zidua. Zidua did have better residual going out under the no cover crop.
Looking at across there, you see that the rye, the light blue colored bar, was higher in all the treatments. So that indicated that having some sort of a ground cover there with the residual did give us more suppression, more control of Texas panicum than the oat and then the no cover. So that was good.
You know, obviously the more tools, more control tactics we put in our production program, the better our success with pest control will be. And I want to put this up here. So, this was the control plot basically.
So, we had no herbicides. This is just cover crop and no cover crop. This is a Texas panicum plant per unit area.
And you can see the rye bar was the lowest, had the fewest Texas panicum plants versus the oats, which is a dark blue. And then the no cover was about 30 plants per meter square. Cover crops will help us.
I know it's more challenging in a peanut production system to utilize cover crops versus our other row crops. I think it's a good tool for us to consider. Here's some pictures of those plots.
The one on the left is the rye, the oat in the middle, and then the no cover. Really the oat broke down really fast. Residue - the rye hung around most of the summer.
We still had good coverage of the soil. And as you can see in the no cover that it's quite a bit of seed heads out there. So, the cover did provide some impact on those Texas panicum populations.
That's all I had today. Thank you for having me. Here's my contact information.
I want to thank the Peanut Board for funding the projects on the adjuvant projects and the cover crop projects. February 6th, the Dicamba labels were vacated by federal court in Arizona. And February 14th, the EPA came out with what they call a limited stocks order or ending stocks order.
And what that means is any Dicamba product that was packaged in the system can still be transported to retailers and retailers can still sell them. Anything before February 6th was not at that stage cannot be sold. I think in the Dicamba training, you'll get some dates on that.
The retailers have a cutoff date. For the growers, it's still the same dates as always. June 30th for soybeans and July 30th for cotton.
As far as 2025, I don't know what's going to be the impact there. Those products technically are no longer available. We don't have a label, so it's pretty much up to the registrants to start the whole process over to get a new label for the products.
So, I don't know what the time frame of that will be or how long that will take. But at least this year we have Dicamba. And that's a wrap up of today's enlightening discussion.
[Hannah Mikell]
We've explored the challenges posed by ryegrass resistance, the potential for Reviton as a new burndown option, insights from herbicide-resistant surveys, and strategies for tackling Texas panicum. Remember, staying informed and adaptive is key to ever-evolving landscape of our agriculture. Thank you for tuning in and until next time, keep cultivating knowledge and innovation in your fields.