Weeds AR Wild Series, S2 Ep19. Salvage Weed Control & Herbicide Cut-offs

Weeds AR Wild Series, S2 Ep19. In this episode, Dr. Tommy Butts discusses salvage weed control across several cropping systems and adds a reminder on herbicide cut-off timings.

Transcript

Weeds AR Wild Series, Season 2 Episode 19. 
Title: Salvage Weed Control & Herbicide Cut-offs 
Date:  June 29, 2022

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


Dr. Tommy Butts: Welcome to the Weeds All Wild podcast series as a part of Arkansas Row Crops Radio. My name is Tommy Butts, Extension weed scientist with the University of Arkansas System Division of Agriculture. On this week's podcast, we're going to be discussing some salvage weed control options. Basically, as we're getting later into our weed control part of the growing season, just trying to finish out our weed control and our different crops and some recommendations for us to do that. So that's kind of what we're going to hit on this week. Just jumping right in, the very first one I kind of wanted to hit on that I’ve probably been getting the most calls on is basically barnyardgrass or other grasses in general and some salvage treatments to try and get that under control, both in rice but also in some of our other crops too.

I know Dr. Larry Steckel and Tom Barber discussed grass control in some of our other crops last week and just the problems that we're seeing. And so we've been getting a lot of calls on grass control this year across our different crops. You know, initially in rice. That's where I want to start. You know, I've been getting a lot of calls there where, “We're going to flood or we're at flood. We got a bad barnyardgrass problem, a bad sprangletop problem,” something along those lines. “What can we use that’s a homerun hitter to kind of get all of this cleaned up?” And really, the best salvage treatments that we've seen in our research plots has been doing a combo of either Ricestar plus Regiment or Ricestar plus Beyond/Postscript if you're in Clearfield or FullPage rice. Both of those combo treatments have looked really great in our research. Now it is expensive. I mean, we're talking, you know, probably $60 an acre there for those treatments. But if we're in a salvage situation where it's either get that grass under control or lose the rice, it's definitely been very good for us in those aspects.

You know, if we don't have a lot of grass pressure out there, if we're not super dense, all those kinds of things, I might yield and save some money then on some of these things. So you always got to balance some of those decisions out there on whether it's economical or not. But definitely if you've got a bad, thick population out there, it's big barnyard. You need to get it under control. These have been a couple of really good treatments for us in research. One of the things I did want to hit on, too, with those treatments is I've gotten a lot of questions, “Well, should we do that preflood or do that postflood?” And what's interesting last year in our research was we actually saw that we got a little bit less control per se. It looked a little weaker when we sprayed it preflood versus postflood. So we actually look like we got better weed control postflood from those applications, which kind of ties in always to the fact that we say, you need some moisture for those to work. You know, those weeds are a little bit less under stress when it's got all that moisture to it. It's probably the herbicides are working a little bit better then. But what was interesting about that was even though we got what we would call better weed control postflood at the end of the year, our yields were better from our preflood treatments by knocking out that weed pressure sooner and having less competition a little bit sooner, we actually ended up with a little bit better yield. So I say all that to say, typically I've been recommending – let's get it out there preflood. Even if we do lose a little bit on the weed control front, it looks like we get better yields on the back end, which can save us economically. Now, that was last year this year's a whole other ballgame when it comes to the environment. We are a lot hotter than we were last year. We're in a much more severe drought than we were last year. That could be a whole different ballgame this year. We may want to lean more towards a postflood where we have some more moisture. Those weeds are a little bit more actively growing. But in general, like I said – especially, let's say if you're in south Arkansas where you caught some rains earlier this weekend, the earlier this week kind of thing, it might be one of those things I'd be I'd be doing the preflood rather than the postflood, and knocking out those weeds a little bit sooner. Because it may save us on our yield.

So, I did want to mention those treatments as far as rice goes. They've been great, both barnyard grass and sprangletop salvage treatments there. In soybean and cotton, there's not a lot of different recommendations that we can go down. Roundup is still likely our best option, our control and our different grasses that we have out there. You can mix Roundup and Liberty together, especially if you're in the Enlist E3 or XtendFlex soybean traits or cotton traits. You want to make sure that obviously you don't make Roundup and Liberty if you have just the standard Xtend soybean trait out there. But mixing  Roundup and Liberty together has been real good for our grass control. You also could mix Roundup with Select, or Clethodim, and you got a couple different modes of action out there too. The only caveat to that, I always say is make sure to use your full rates. Don't cut your rates on either one of those because that's not beneficial at all. So make sure you use and full rates if you do have that mix.

The other thing, especially and Tom and Dr. Steckel discussed this a little bit last week too, but with some of the hot conditions we've got, we do have a pretty high variability in our spray waters that we have out there. You may consider adding ammonium sulfate or AMS into that tank too, just to help with some of those hard water concerns or tying up some of those cations to make sure our herbicides are free and available to do their job. And normally AMS is a fairly cheap addition to the tank. So again, it might just be a reasonable safety net to kind of help us out there with some of these applications and maybe gain us some extra control as well. Now, along these lines, I did want to really reemphasize again, if you're in the dicamba system, if you're in Xtend or XtendFlex beans or cotton, make sure that we're taking out Select or Roundup out of our tank mixtures.

Now, Roundup and dicamba is an illegal tank mixture in Arkansas. So, I want to stress that it is it is illegal. We can't mix those two in Arkansas. But even outside of those regulations, with the severe antagonism that we see when we're looking at those tank mixes – whether it's Roundup with dicamba or Select with dicamba, we just do not want to be using those for weed control because of our loss in that weed control. And just as an example, we had a trial down in Rohwer last year that we sprayed with a tank mixture of – well, we did the individual components, glyphosate and dicamba, and then we did a tank mixture of those two in a in a couple of small plot research studies. And just as an example with pigweed control, if we were looking at dicamba by itself, four weeks after application we had zero pigweeds in that plot. If we looked at dicamba plus glyphosate, we actually had 11 pigweeds per meter squared. So, you know, in a three-by-three foot square, basically we had 11 pigweeds because of that tank mixture. If we look at barnyardgrass control down there, if we looked at just plain glyphosate, nothing else in the tank, we had zero barnyardgrass plants in that meter squared.

But as soon as we did that tank mix, we also had 9 barnyardgrass plants per meter squared. So that may not seem a lot, but if you start thinking about a three-foot by three-foot square and you've got 11 escapes of pigweeds and nine escapes of barnyardgrass versus zeros, if you could make those applications by themselves, that's a pretty big deal. That's pretty significant loss in control just because we ran that tank mixed together. So again, separating those applications out in the dicamba system is pretty critical to make sure we're maximizing the control both for grasses and for pigweeds. And that again applies to both Clethodim or Select as well as glyphosate. Which again, glyphosate is an illegal tank mixed partner in the state of Arkansas. I want to stress that again. 

So with our grasses, those are really our best options right now that we can look at as far as trying to manage those across our different crops. Another weed that I've been getting a lot of phone calls on happens to be the sedges again, still. You know, yellow nutsedge has kind of died down. But if you're still battling yellow nutsedge out there, our ALS chemistries are still the way to go. Permits, Permit Plus Gambits even later in the season. I will say, you know, particularly, let's say with Gambit, depending on your soil type and what you're planning on planting next year, you may want to kind of watch out for that plantback interval to for Gambit if you're going to soybeans next year, that kind of thing. So just be aware of some of our plantbacks with some of these later season applications that might be going out. And those the Permit, Permit Plus, Gambits of the world, are obviously for rice control with yellow nutsedge. If we're in soybeans or cotton, we don't have a lot of great options for yellow nutsedge. You know, there's things like Roundup Plus Liberty, maybe Basagran plus Roundup. Roundup by itself, just a single application is not great. But, maybe if you hit it a couple different times, which we're getting late in the season here now to be trying to do two or three applications of Roundup. But if you can do multiple applications, it'll knock it back or suppress it, at least that your beans and cotton should be able to get up on top of it, that kind of thing. I have been getting a lot of calls on annual flatsedges too, not necessarily in soybeans and cotton. We can battle annual flatsedges pretty easily in those crops. But in rice, I've been having a lot of calls recently trying to battle this right before flood or even after flood. And one of the things I wanted to mention here is I really do recommend, if possible, going towards Loyant in these later season situations. Primarily because it's a systemic herbicide. So you can get a little bit less on the plant, but because it's going to move through it, you still can get a good kill. So I tend to, if possible, lean towards Loyant later in the season for some of these annual flatsedges. Now, I know that comes with its own caveat of things. So if that's not an option, Basagran plus propanil is still a really good treatment. It just gets a lot tougher to get the coverage that we need when our annual flatsedges might be a little bit smaller than our rice. Our rice is getting big and getting closer to canopy. You know, we're still trying to get coverage with those with those contact herbicides. It just can be tougher to get control when we're getting later in the season here, the rice is bigger. Those sedges may not be quite as big. They're still a little bit small, but they're there. It's just a little bit tougher to get full control with contact herbicides. So that's why I tend to lean a little bit away from that if I can, but still good options. 

Another couple options, especially when we start considering salvage type situations with the annual flatsedges that I wanted to mention is especially in rice. If we go to flood and we got these things that start breaking through postflood – through the canopy, Loyant coated on fertilizer may be a good option in this situation. You can drop that coated fertilizer into the flood and you still get good flatsedge control and it reduces the drift potential. So it may be an option, how we can get Loyant out there for flatsedge control and reduce some of that drift potential. Also, we do have Rogue postflood as an option. Now that comes with its own caveats, right? We need zero grade or straight levied fields to make sure that we can hold the water. We want to have a deep flood held because the deeper the water, the better it's going to work. We need to use MSO. That helps heat it up. A larger droplet size and more volume can help us with that application. Make sure we're getting that spray down to the water and not get caught up in all the plant material and leaves and everything else. We need to get it to the water. So there's a lot of different things we need to do to maximize that effectiveness. But when we do that, Rogue is very effective on our annual flatsedges and so can be a great postflood option and knock some of that stuff out as well. 

So, a whole handful of options there to hopefully to start battling those annual flatsedges. Like I mentioned, if I could lean towards the Loyant route, I really would. Whether it is a foliar application or trying to coat fertilizer and drop it in the flood, they both should be pretty effective. Rogue postflood is very effective. And then if I can, as long as I know I can get good coverage, the Basagran and the propanil still should work too. It's just that coverage issue that makes it a little bit more challenging there. 

That really hits on grasses and sedges that I've had a lot of calls on there. I haven't had a lot of calls this year on pigweeds breaking through yet, where we're maybe still a little bit early for having to be concerned with salvage options there. But I figured I might as well hit on it while we're talking about salvage options. In rice, especially if we're talking row rice for pigweeds, Loyant is still our best option there to knock out our pigweeds. Again, tough to apply, but if we can get it out with a ground rig, Loyant is great at knocking down our pigweeds. I will say here I just got done talking about Loyant coated on fertilizer. You know, dropping it into the flood is good for flatsedge. Coating Loyant on fertilizer and dropping it onto the ground like, let's say in row rice will not work for pigweed control. So, that's not an option here. We do have to foliar spray Loyant to make it work for pigweed control. We can't coat it on fertilizer and drop it on the ground for row rice and expect pig weed control. So just be aware of that. And if you want more details to on coating on fertilizer with Loyant and those kinds of things, Dr. Norsworthy and one of his graduate students, Bodie Cotter, did a podcast just a few weeks ago. Check that out and can get some more details there, too, on that process and what's worked and what hasn't worked, that kind of thing. 

The other option in rice, too, is still the old standby of Grandstand and propanil. You know, it can do a pretty decent job if you're in a pinch. It's not a home run hitter per se, but it'll definitely knock those pigweeds back quite a bit and give you give you definitely some burn back and some kill out there if you just need to get rid of some at least, and that's your only other option. So be aware that that that still is a pretty decent option, at least. In soybean and cotton, when we're talking there as far as late season pigweed control, there's not a lot to say. But the big things that I wanted to hit on if you're in the Enlist E3 system, Enlist One plus Liberty, that tank mixture is really, really good. It's really hot. It knocks out pigweeds really well. So doing that tank mix is pretty critical to have successful pigweed control, especially if we're getting later in the season. They're starting to get hardened off. It's hotter, all those kinds of things. That's been real successful for us, that tank mixture. With the dicamba system, if you're an Xtend or XtendFlex, because we cannot mix glufosinate or Liberty, and we cannot mix – while that's main one, I guess, for pigweed control – we can't mix that in the same tank load. We really need sequentials, right? We can't rely on just a single application. So, we got to have sequential out there. 

And so, most of our research has shown if we can get our dicamba out first, and when I say first, I mean now because this is our dicamba week. The cut-off is coming up here. I'm recording this on June 28th and the cut-off is June 30th. So, if you hear this, you have a day maybe. But if you're hearing this after June 30th, the cut-off is passed. And so we're probably past that point. But if you can get dicamba out now and then in a couple of weeks, follow it up with a shot of Liberty. That has been lights-out. Doing dicamba and then following it about 10, 14 days later with a shot of Liberty. It's done a really good job of cleaning up pigweeds as well. So just be prepared that you need that sequentials in that system. So again, that kind of hits on the pigweed front, too. That's our current best options as far as that goes. 

If you're outside of the Enlist and Xtend systems and you're in LibertyLink or conventionals or anything else – conventionals, we’re really very limited in options this late in the season.

If you haven't used up your PPOs yet, you can try those. But otherwise, you almost just need a chopping crew, which is no fun. But that's about where we're at there. In Liberty Link, if you can just still hit it with a couple more, another shot of Liberty or if you haven't used one yet, a couple of shots of Liberty, that's really the route you need to go there too. We just don't have a whole lot of good POST options in those systems anymore, especially late in the season like this. So I wanted to mention that on the pigweed front. Those are really the three main weed species I want to hit on. Some of the grasses, the sedges and the pigweeds. So those are the main things I wanted to hit on there.

The one other tidbit of information I wanted to throw out there that I've been getting phone calls on, and that kind of rolls into this conversation where we're talking later in the weed control portion of our season here – is herbicide cut-off timings, right? And so, we're really starting to hit that window a lot. We're getting to the end of when we can apply herbicides. I already mentioned it, but just to hit on it again this week is the dicamba cut-off. June 30th is the final day that we can apply dicamba. So, if you're listening to this before or after, just be aware that that that is our cut-off there. Also, for all a lot of our other herbicides we have cut-offs. Whether it's a preharvest interval – whether in soybeans, for example, we have R1, R2 cut-offs. A lot of times that flowering cut-off type thing, because we might knock buds off if we apply too late. So just be aware, we're really starting to reach a lot of those windows where we need to cut-off our herbicide applications, too. 

And if you have more questions about that, we do have a publication, a handy little guide available for you. It's our MP 566. It's called Application Cut-off Timings for Common Herbicide. You can get that from your local county extension office or download it online, or feel free to get a hold of me and I can get you a copy as well. But it's a handy little reference guide for a lot of our different herbicides and what their cut-off timings are. And then just along that same line of thinking too, we do have the MP 567 publication which is the Max Use Rates per Application and per Season for Common Herbicides. So a lot of times we're getting here to the end and we need to just finish up making sure that we're following those guidelines and not going over our use limits. There's a little handy guide for that, too, that you can check out. Just so you know where you're at as far as that goes, too, for label requirements on use limits. So, check out those publications. Like I said, your local county office should have one. You can either talk to your county agent or get a hold of us as well and we can get you a copy. Or download one from online as well. They're free for use.

With that, that pretty much hits on all the topics I wanted to hit on this week, as far as our salvage weed control kind of goes and those herbicide cut-offs. As always, if you ever want to get any information, please check out our website, uaex.uada.edu/weeds. Your local county agent is always a great source for information, so make sure to visit with them at the county office and make sure to grab an MP 44 to have on hand or download from online right on your phone. Thank you to all of those who have signed up for our texting service. If you haven't done so yet, please do so. We send out a lot of great info through that. All you have to do is text W-E-E-D-S to (501) 300-8883. Make sure to check that out. And then as always, if you ever have any questions, concerns, discussion points, or just want to chat, feel free to give us a call at any time. Shoot us a text, that kind of thing, and we can have a discussion as well. We're always available to try and help out as much as we can when it comes to the weed control portion of your crops out there. 

Final thing, I just again want to say some thank you-s. You know, thanks to the Arkansas Commodity Boards for their funding and support of our research and extension activities, as well as some funding I've received from the USDA-NIFA and USDA-ARS. You know, all of that funding helps contribute to the research that drives these recommendations as well as these extension activities or opportunities that we get to do to get this information out to all the general public. So thank you to all of those funding sources. It's much appreciated. And again, it allows us to effectively do our jobs, to the best of our abilities. With all of that, I just want to say thank you again for listening and continuing to listen to this podcast series. If you ever need anything from us, please feel free to get a hold of us. So with that, thank you for joining us for this episode of the Weeds AR Wild podcast series on Arkansas Row Crops Radio.


[Music]: Arkansas Row Crops Radio is a production of the University of Arkansas System Division of Agriculture. For more information, please contact your local county extension agent or visit uaex.uada.edu.