Weeds AR Wild Episode 23 
Title:  Soybean Harvest Aids
T. Barber, J. Ross
Date:  August 25, 2021

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

Tom Barber: Hello and welcome to the Weeds AR Wild podcast series as part of Arkansas Row Crops Radio. This is Tom Barber, extension weed scientist with the University of Arkansas System Division of Agriculture. Today I have Dr. Jeremy Ross with me. Jeremy as you know is our extension soybean specialist. What’s up Jeremy?

Jeremy Ross: Hey Tom, good to be here today.

Tom Alright. Good to have you. I know we’ve visited a while coming into work this morning and we have both been getting a lot of questions I guess about soybean harvest aids and usually what the first question is, when can I start spraying some of these fields to get the ball rolling and get our combines rolling this year? So let’s talk about a little bit about timing, growth stages, when some of these consultants and or growers can make some desiccation applications and move on quickly towards harvest. 

Jeremy: Yeah, my phone’s been really kind of blowing up in the last week and I guess it is that time of year to get ready to start harvesting, it just doesn’t seem like it should be that time with some of the problems we’ve had. But with the late plantings that we’ve had in some parts of the state I am starting to get a number of questions from consultants and growers and county agents on what are our recommendations and when can we go? So the very first thing we really need to be thinking about is what growth stage can we actually apply harvest aid and not see any kind of yield loss due to that application? And so from research that we’ve conducted here at the university and looking at states, other states in the mid-south, our recommendation is any time after R6.5. And so the big question is exactly when is R6.5? Under normal growing conditions a soybean plant can reach the 6.5 growth stage about 10-14 days after the R6 growth stage. And so you know we have a good strong definition for what R6 is, so the definition for R6 is one pod containing a green seed that fills the pod cavity at one of the 4 upper most nodes on the main stem of the fully developed leaf. And so once we get to growth stage 6.0, sometime 10-14 days after that is when we should be able to reach 6.5. If we go out at growth stage 6.0, if we open a pod, the membranes are still going to be attached to the seed and so at that point moisture and nutrients are still going into that seed to continue to fill that out. Once we get to R6.5, if we pull one of those pods at one of the 4 most upper most nodes on the plant, and we open that pod up the membrane should separate very easily from those seed and we’ve reached R6.5 growth stage and then nothing else is going into that seed. It’s reached its maximum size. And so from the research that we’ve conducted here, we haven’t really seen any kind of significant yield loss once we get past that R6.5 stage. The key is I’d rather be later than earlier. If you have any hesitation or doubt exactly what growth stage you’re at, by all means I’d give it another 5-7 days just to ensure that we’re past that critical growth stage. Because looking at the data if we go as early as R6.0, we’re looking at a 56% yield reduction by going 10 days too early. So I always caution people not to go too early because we can have some significant yield loss and quality issues if we pull that trigger just a little bit too early. 

Tom: Yeah and I know we did some of that work Jeremy several years ago, and back when Jim Griffin was with Louisiana State University, collaborated some with him and his program on harvest aid timing and Dr. Daniel Stevenson as well and you know hitting that 6.5 stage is kind of tricky. At least when I’ve gone out and even in our small plots and tried to determine when 6.5 was and seems like sometimes a couple of reps may be there on one side of the test and the other side we weren’t quite there yet. So I think after all that because it’s so critical that we wait at least until that point and when we get on a large scale basis to try to determine when 6.5 is, basically the conclusion from a lot of that research that we did back then was let’s just wait until R7 and we know we’re safe. 

Jeremy: Absolutely and we know when we are at R7 because the definition of R7 is one mature colored pod anywhere on the main stem, so at that point a majority of the pods on the plant, the membrane should be able to be separated from those pods. So nothing else is going in to fill up those pods and so I absolutely agree that I would rather be on the later side than the early side. And then once we do get to R7 we shouldn’t have any yield reduction due to the application. 

Tom: And so you’re saying R6.5 when you look at those top 4 nods for that, but R7 is just a brown pod anywhere, it doesn’t have to be in those top nods.

Jeremy: Absolutely, so anywhere on the main stem as long as we got a mature colored pod, we’re at R7.

Tom: Aright. So once we get timing down and another thing on timing and products really, we have, most of you know about our MP44 publication. That’s a yearly publication we update and release. It’s a fairly large book but it’s our recommended chemicals for weeds and brush control. This is something you can find on our website. That website is www.uaex.uada.edu, isn’t that right Jeremy? 

Jeremy: I think that’s right.

Tom: So a lot of times if you just google MP44 it’ll pop up, but over on page 60 is where our soybean pre-harvest or harvest aid section can be found and it lists the products that are currently labeled for harvest aids. And so there’s just a handful of them. Paraquat, several formulations of Paraquat are labeled. Glyphosate is labeled at that time. Sodium Chlorate, Aim and Sharpen. Aim and Sharpen are PPO’s. We’re somewhat familiar with those, but Gromoxone or Paraquat by far gets the majority of the harvest aid work or what people are putting out just because of its effectiveness and how quickly it will desiccate the crop, but if you look at under time of application, on page 60 in MP44, you’re not going to hear any of these R6.5 or read any I guess. R6.5 or R7 recommendations basically because those are not on the product labels. And so most of the product labels that are labeled for harvest aids in soybean are going to talk about when half of the soybean leaves have dropped and the other half have turned yellow. Or when 65% of the pods are brown and remaining pods are turning yellow. And so when we have that kind of leaf drop Jeremy, what we’re talking about 60% leaf drop, even 50% leaf drop to some extent, how far do you think we are from being able to harvest those beans without a harvest aid?

Jeremy: Well under normal conditions, we’re probably14 days, 21 days, depending on how much moisture are in those pods. But we’re not too far off once we get to that growth stage and start losing the large amount of our leaves that are on the plants.

Tom: Right and so if we do go at R7, that’s probably a little sooner than that 50% leaf drop, wouldn’t you say?

Jeremy: Right, after the soybeans have turned color.

Tom: So that means we’re going a little earlier than what the products are labeled for, but through our data we have found that we can go that early, like Jeremy was saying earlier and be safe at least from a yield standpoint. But if we trigger it at R7, it’s going to take a little longer for some of these harvest aids to work. And so one thing we need to talk about is the harvest intervals after application. So any of the Paraquat formulations have a 15 day harvest interval. And that just means we’re suppose to wait 15 days prior to putting the combine in the field. Now in a lot of cases if the beans are further along, it may only take 5-7 days for that desiccation to take place. And so we just need to be mindful of our harvest aid or harvest intervals following these harvest aid applications. Now we get down to something like sodium chlorate or Aim and Sharpen, Aim and Sharpen specifically have a 3 day harvest interval and I believe sodium chlorate does as well. Again this information is in the MP44. You can look that up just to read the rates of what you need when. But again Gromoxone or Paraquat is going to be a little faster acting product, but we do need to wait that 15 days prior to putting the combine in the field. And if we go as early as R7 I think in a lot of cases it may take close to 2 weeks for them to get ready anyway. The earlier we go the longer it will take to get all the leaves dropped and for those stems to dry up. So the next thing we probably need to talk about is drift. So just be mindful when making these harvest aid applications that there’s a lot of other crops in the field. Gromoxone or Paraquat drift can be detrimental to a lot of crops in the neighboring fields that are not fully mature yet. Rice, cotton, we use it as a defoliate in cotton but we don’t want the leaves falling off until it’s time for the leaves to fall off of cotton and so we just need to be mindful of our surrounding fields and the crops in those fields to determine what harvest aid we use and how we apply that. And in some cases it may not be safe to apply. But usually this time of year when I get these questions I think for the most part growers are just wanting a place to start, right Jeremy? Find some fields to start and get the combines rolling. 

Jeremy: Yeah I think with the problems this year everybody is just ready to get this year past them. So I think a lot of them are just anxious to get going and so this is a way to try to at least try to get the combines in the field. You know, a couple of things I wanted just to kind of mention too, is I get questions all the time, are harvest aids going to help draw down that moisture in the seed, and really the answer is no as a direct application. Now as the plants dry down and desiccate you will start to draw down that moisture, but applying Gromoxone or some of these others, we’re not going to actually just draw the moisture out of that seed because those pods are pretty tough and you’re not going to be able to get a lot of this chemical into the pod through the seed to help dry it down. There are some reports that sodium chlorate may help a little bit with that but as a general rule if you’ve got green seed out there applying this harvest aid is not going to draw that moisture out directly. And then the other things is, you know I caution farmers on once you desiccate a soybean plant, there’s nothing good that’s going to happen to that plant until you get it into the truck to haul it off from the farm. And so just be cautious, don’t apply too much harvest aid to too many acres that you can’t get across in a timely manner. The worst thing that can happen is desiccate a bunch of soybeans and then we get a hurricane in here that we’re not able to get into the fields for an extended period of time and any kind of weather event after you put on a desiccant you can start seeing quality issues. That’s probably the main thing, but we can also see some yield loss. We can start seeing some of these pods starting to split and having shattered in some of these plants. So just kind of be cautious. Don’t go out there and treat the entire farm. I’d do it in blocks. If you can get across several hundred acres in a weeks’ time, do that, then come back a week later and do some more. And just kind of stagger it and not have everything treated at the same time. 

Tom: Yeah and I guess the other thing we talked a little bit about products and harvest aid, but just rates for those products and mixtures. I think generally when we talk about a harvest aid program, again most of the time it’s going to have Paraquat. That rate of Paraquat, if it’s the old 2 lb/gallon Gromoxone, which I don’t know how much of that is still out there, It is a 1pt/Acre rate of that product, most of our Paraquat formulations are 3 lb/gallon now, that’s 10.67 oz/Acre in one application. And again I think that if we put some surfactant in there, that’s going to give us some better results and also I like mixing some sodium chlorate in there, so Paraquat, plus 3-6 pounds of chlorate or we can add 1oz of Sharpen or Aim to that, if you need some extra burn on some weeds that are out there. Just check the surfactant on which product we add with the Paraquat. If we’re going out and we need to harvest quickly, Sharpen is probably our best option. One to two ounces of Sharpen, the more the better from a desiccant standpoint and then adding the chlorate to that in my opinion is a must as well, and then we can harvest in 3 days. So other than that, Jeremy any other thoughts?

Jeremy. No, but we talked about a couple of different publications. We talked about the MP44 and also there’s really good publication on our website that describes the soybean growth and development and so we’ve talked about a couple of different growth stages and that particular publication has very good pictures and good descriptions of all the growth stages, so again you know if you’re wanting to look for these publications just go to www.uaex.uada.edu and both of these publications should be on the soybean production website on our webpage and so if you do have any questions you can drop me an email or give me a call and I’ll be more than glad to try to point you in the right direction. 

Tom: Alright, well that’s some good info. Check our website. We have a lot of good publications there. We want to thank everybody for tuning into this episode and want to thank Jeremy, special thanks to Jeremy for joining us and actually calling me this morning and saying hey Tom we need to do a podcast. I agree 100%. 

Jeremy: I appreciate it Tom. And thank y’all for getting this going and I probably really need to do some more of these podcasts, but again I appreciate y’all allowing us to do this on y’alls podcast. 

Tom: Alright man. It’s pretty special. It takes a special individual to be invited. And to be honest, I’m not sure when the next one is even going to be. We’re kind of playing these things by ear right now just because it’s kind of end of the season. As topics arise we talk about them, so hope everyone has a great week. Again want to thank everybody for joining us for this episode of the Weeds AR Wild podcast series on Arkansas Row Crops Radio. 

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