Getting the most out of pre-emergence herbicides with Dr. Tom Peters and Dr. Debalin Sarangi
Good day and welcome to the University of Minnesota podcast Minnesota CropCast. I'm your host Dave Nicolai with University of Minnesota Extension. I'm a field crop agronomist in the University of Minnesota Extension. I'm here along with my cohost Doctor. Seth Nave, University of Minnesota Extension soybean specialist.
David Nicolai:And Seth, here we are in early May. We've had some good planning progress across the whole Upper Midwest for that matter But certainly in parts of Minnesota, I know parts of Western Minnesota have made quite a bit of progress considerably more even perhaps than on the Eastern Side of the state. But I hear variations 75% to, you know, probably as little as 25 or 30% depending upon how much moisture. But before I let you jump in, Seth, we have on our guest today Doctor. Tom Peters, University of Minnesota and North Dakota State University Extension Sugar Beet, a specialist in weed control.
David Nicolai:And then also Doctor. Demin Saranger, University of Minnesota Extension corn and soybean weed scientist. And Tom, I know things always start a little bit more to the West than they do to the East. How are things looking in terms of planting progress, not only for sugar beets, but for other crops as well?
Speaker 2:Tremendous progress on sugar beets, Dave. About 500,000 acres or 82% of our crop is planted. We had tremendous conditions for planting. It was a little bit on the dry side which enabled the soils to work well and we've been blessed to receive some rain last week anywhere from one to two maybe even two and a half inch in sugar beet growing regions depending on where you live. So we're off to a fantastic start on sugar beets.
Speaker 2:Most of the small grains are also planted but not a lot of corn and soybean progress in the Northwest Minnesota, Northeast North Dakota at this point.
David Nicolai:I know on the eastern side of the state a little bit less. Devlin, you had an opportunity to get out and look at the Rosemont area and other areas of the state. Soils are warming up, but I think some of the crop and maybe even the weeds have been slow here too. What do you see for planting progress?
Speaker 3:Oh, Dave, I mean, we got some rain last week and some and that brings some moisture in the field. So I saw some progress definitely, with soybean and corn, but, as you mentioned, I am hearing the Western part have made more progress than Eastern part. And I'm a weed scientist. When I am out in the field, I look for the weed emergence. And, I saw those biennials and perennials are, already there.
Speaker 3:And when you talk about the annual weeds, I found quite a bit of lambsquarters and ragweeds. They are germinating in the southern part of the state. And with the warm temperature that is this week and that's upcoming, I'm expecting a lot of pigweeds will come out. And I was discussing with Tom a little bit that whether he found anything in the Western part yet, but his prediction also the same that some pigweed emergence is expected this week.
Speaker 4:So what what do you think? How much early are we? Is that a week early? A couple weeks early than than normal? I know it's hard to say what normal is, but, what I guess this is kind of that topic of phenology.
Speaker 4:Right? Studying the environment and understanding how those things vary, from year to year in terms of their growth stages.
Speaker 2:I think in
Speaker 3:the Western
Speaker 2:part of the state, I I think, Seth, we're we're ten days ahead of schedule. That's a bold number, but that's the way I feel about it. When you look at the numbers, I'm I'm I think we're ten days.
Speaker 4:Are you ten days ahead in crop progress or in the weed and and just environmental conditions?
Speaker 2:I think in crop progress. So I'm like Dublin. I I see a lot of common lambs quarters. We also have plenty of kosher out here so I see that. Haven't seen any waterhemp or heard any reports of waterhemp but fully expect to get those this week.
Speaker 2:Certainly by the end of the week, I think waterhemp is going to be widespread.
David Nicolai:In terms of you know situations, one of the things that you folks have been involved with weed control. Recently there is a crop news that you were both co authors on and along with the graduate student as well. In terms of pre emergence herbicide and people can find it on Minnesota Crop News by the way, that article was quite extensive. What are some general things we should keep in mind you know in terms of that we certainly think about RAIN and activation. But what about for folks that have planted in in terms of catching up with this weed emergence and whether the weeds are there or not, maybe talk a little bit about that, how that works in in terms of that.
David Nicolai:You know, sometimes people are a little reluctant and say, I really don't want to put it out there until I know it's gonna rain. You know, there's a lot of things that go into that and there's a certain amount that the crop news talks about different types of chemistry as well. And we don't have typically a lot of crop actually emerge per se, but we can discuss that next. But let's talk about this impact on timing and rainfall and the need for pre emergence as we get into this warm week.
Speaker 3:So, Dave, you are referring to the crop news article that came out, recently. And, one of my grad students, he pulled all the information from different sources to put into that crop news article. And that article titled getting the most out of pre emergence herbicide. It starts with your soil. That grad student, Sithin Matthew, he's also with me today, he can chime in.
Speaker 3:So I'll just, give you a little bit overview where this article is coming from. So every year, during this time, like spring, I get some phone calls from the farmers. Either they talk about, okay. I put my crops in the ground and it's really dry and not much moisture in the ground. I don't know whether I should spend some money on, pre emergence herbicide or not.
Speaker 3:Or they would say, like, okay. I, I saw some carryover issue from last year's herbicide, and it's injuring my beans or corn. So we thought, like, okay. Let's, this is probably the right time to put together an article that will talk about different chemistries and soil type and how the soil that impact the chemistries. So, mostly, we are talking about the preemergence.
Speaker 3:We are not much talking about the carryover issues. But, you know, like, if you if you think about how the herbicide works, I mean, the the herbicide efficacy that depends on couple of the factors. Right? One is definitely the moisture and temperature. That's a big factor, but also how the herbicide is retained by the soil.
Speaker 3:So retention of herbicides and the solubility of the chemistry of that herbicide and also its persistence, like how persistent that herbicide in the soil or soil, solution or soil water. So, we mostly talked about those things, how the chemistry is impacted by pH, impacted by soil organic matter, impacted by the herbicide chemistry type, and their half life persistence. So that was mostly the focus. It is more like an educational effort from me, Tom, and the grad student. We wanted to put this information out so that people are the people can read about it and think about which herbicide I'm putting, what kind of soil I have, and what I can get out of my soil when I'm putting this pre emergence herbicide.
Speaker 3:And, I have the graduate student who pulled all the information and put together this article, and he is with me. And I would probably ask him to introduce himself and maybe give one or two sentences on this article. Sithin, actually, we cannot hear you for some reason.
David Nicolai:We might come back to visit with Citi in a little bit more in Yeah. We
Speaker 3:can come back. Yes. Yeah. Yeah. So Tom is also here.
Speaker 3:And Tom, you can chime in because you are also part of that crop news article, and you can chime in. So
Speaker 2:65% of sugar beet growers identify pigweed especially waterhemp as their most important weed. And I'm going to venture to guess another 15 or 20% would have pigweed as their second most important weed. So the best way, the only way to control water, hemp and sugar beets is with soil residual herbicides that are applied and activated before the waterhemp emerges. So we've created a culture where if you want to be successful, you've got to use a pre emergence herbicide. So in the article, Sitton did an excellent job of talking about the water solubility of different products and how that equates to longevity and I'm gonna give you an example of how we use that to our advantage in sugar beets.
Speaker 2:So a lot of times, the pre emergence program is a combination of two active ingredients, one called ethafumazate which is a common name, there's a lot of brands by which it's sold by and then the second herbicide is dual magnum. Dual magnum is the only herbicide that is approved pre emergent in the chloroacetamide family pre emergence. So we put those together because it takes less water to get dual magnum activated as compared to the ethafumazate products. So it's an effective one two punch where we get the early activity from dual magnum which buys us a little time to get the ethafumazate, activated. But like I was saying, we were very very fortunate in that we did receive rain so from what I can tell both of our actives that we're using in sugar beet have been activated by rainfall and are available for waterhemp control.
David Nicolai:Can we extrapolate that, Debalin, a little bit on the corn and soybeans taking off and what Tom mentioned in terms of dual? Are there some other herbicides? I don't know if there's some examples if you want, so I didn't want to chime in here that have done well. They don't necessarily require an extraordinary amount of water for activation from a solubility standpoint. I think there are some things mentioned in the crop news for certain about that.
Speaker 3:Yes. So we talked about mostly the corn and soybean herbicides in that crop news article. And if you think about some of the herbicides like Spartan or Valor, so those herbicide probably has a little bit low soil mobile mobility, but they are really water soluble. And so
Speaker 2:and
Speaker 3:also, you know, like, we talked about some of the herbicides that can be applied after crop emergence, but some of the herbicide you have to apply before the crop emerge. For for example, if you are applying Valor or Fierce, the time you can apply those herbicide is three days after plant within the three days after planting. That means before the soil is cracking because otherwise, it'll injure your soybeans. So, we talked about those things as well in that article because, some herbicides like, Duo or Warrant, those are labeled for pre and post in soybeans. But some herbicides are strictly pre emergence.
Speaker 3:That means you have to spray before your crop is emerged. And, again, those herbicides will not control any emerged weeds. If the weeds are emerged, they will not control them. But the dual or warrant will not injure your crop if they're out. But, the product like PPO herbicides, like, they will injure your crops severely.
Speaker 3:That's why we call, we talked about when you should, spray those herbicides within how many days. And, you know, like, if the herbicide is more soluble and more mobile in the water or soil, they're more prone to leaching. So you got heavy rainfall, that's herbicide will leach down. On the other side, if the herbicide is, like, not, much soluble, they're, like, staying in the top layer of the soil, they're more prone to runoff. So if you get a heavy soil and heavy rainfall, they're more prone to runoff and, contaminate the surface water if you are in a sloppy land or and you have a steep slopes.
Speaker 3:So we talked about those things in this article as well.
David Nicolai:So certainly there's a list of those for people if they want to go back and look at that. And and again they can just search for University of Minnesota crop news and it'll come up and you look down for the pre emergence herbicide article was in the last week and a half with that. Are there are there any general rules of thumb? Maybe there are for sugar beets but corn and soybeans and so you know what would be an ideal time frame for how soon or what your idea should be in terms of getting that pre back on the field after planting to take advantage of that? Obviously you know you can go to a certain period of time, but I don't know, Tom, you first maybe on the beets, but maybe your observations even on other crops as well.
David Nicolai:What what kind of a time frame if if you can be timely on it?
Speaker 2:I think we should we should do this in two parts, Dublin. One part is when should we get our products on and then second, what if it doesn't rain? We should also address that. So I'll take the first part. I as a rule of thumb try to get the pre emergence products on within three days of plant.
Speaker 2:So I give it a range because sometimes it's windy. For those of you that don't get out to the Northwest part of the state too much, the wind blows a lot here so we can't always spray because of windy conditions so that's one component of it waiting for the winds to die down. The second component, a lot of times we're using nurse crops or companion crops with our cultivated crops and the soil residual herbicides if they're applied and activated immediately will damage the companion crops. So one strategy is to give them a head start by waiting on rain, excuse me, waiting on spraying them. There aren't as many companion crops used in corn and soybeans but I think the rule of thumb still applies to get them up on within three days or so of of planting.
Speaker 2:And Deblin gave you an outstanding reason for why you wanna do that to especially with soybean with cracking. Deblin?
Speaker 3:Yeah. So, no. I agree with you, Tom, and I agree with that three days time frame because sometimes the farmers are, lagging behind with the planting, and sometimes they don't have time to spray immediately. But, you know, if you start with a conventional tillage, I assume your field is pretty clean, and then you planted your crop. And then, within the three days, if you don't put your pre's down, the weeds will start emerging.
Speaker 3:Those pre emergence herbicide, they don't control the emerged weeds, most of them. So that means you'll, those weeds that are already emerged, they will not be controlled because how those pre emergence herbicide works. So you spray the herbicide, that herbicide goes to the soil solution, and then the emerging weeds so it reached to that top, whatever the four inch, layer of the soil, it stays there in the soil solution. And then when the weeds are emerging from the top four inch layer, they take up those, herbicide from the soil soil solutions, and that's how they got killed. So, either they take that up by roots or by the emerging shoots.
Speaker 3:So if you don't put those herbicides within those three days, the weeds will be up, and then they will less likely to uptake those herbicides. That means those herbicide either they will leach down to the lower, soil profile, so they will not be available to the weeds, or they will be, fixed with the, soil particles, which is, negatively charged. So, so the herbicide will not be available for those weeds. So that's why it is very important to have those, trees down within three days. And, you know, then you can avoid a lot of complexities because some herbicides, you can spray, after three days.
Speaker 3:Some herbicide, cannot strictly by label, you cannot spray after three days of planting. So you can avoid all those complexities.
David Nicolai:So basically, know, you have to look at that label, but I'm gonna just throw you a complex situation for both you and Tom and that is with this warm weather that's predicted this week and rapid wheat emergence, Is there an opportunity to tank mix both a pre and a post together? Would you recommend that in these situations where say for example you haven't had a chance and you also already have some small lambs quarters etcetera coming up where you want to make a two approaches, should you make two passes or what's your thought pattern on that if you haven't had an opportunity to do that and you already are dealing with some very small seedlings emerging?
Speaker 2:Go ahead, Devlin.
Speaker 3:Okay. So yeah. I mean, Dave, that's a very good questions, and that's pretty, like, normal scenarios with farmers. Like so, yes, in some cases, you can tank mix a post with a residual herbicide and kill, you can kill those small seedlings that already emerged, and also you can take care of the future emergence. But remember, you again, you have to come back with a post emergence spraying because this residual herbicide will take care of your weeds for next two to three weeks.
Speaker 3:And after that, the weeds will come come out. So you have to come with another pass of post emergence herbicide because your within the three weeks period, your crop canopy will not be closed. That means the weed emergence will continue to happen. So that means you are adding a cost to your herbicide program by adding a post emergence herbicide at the beginning as well as you will have a second pass. So I'm not saying it is not, it is not possible or not many people do it.
Speaker 3:They do it because they are probably lagging behind, and they check the label. If the, if the label allows that residual herbicides to go down with the post emergence, they have tank mix and spray. But again, you have to come back with a post emergence treatment.
Speaker 2:Tom? I wanna give an example in sugar beets. So our sugar beets are primarily planted into conventional till soils. So we don't have any weeds that are emerged present when we're making pre emergent sprays. However, we have a growing trend occurring and that's called strip tillage.
Speaker 2:So strip tillage is like having no till and conventional till in the same field and we're very, very careful to evaluate both parts of the system, the non tilled area versus the tilled area. So it is very common in those situations to mix a post emergence herbicide in at planting with the soil residual herbicide because we want to get those small lambs quarters or kochia before they start to develop and we'll do that right at planting with that soil residual herbicide combined with a post emergence product.
David Nicolai:Well not necessarily to name names, but Devlin following that strategy are there some common products that people are using? Are they doing a glyphosate, a glufosinate and so forth in this kind of a situation or some other broadleaf herbicide?
Speaker 3:Yeah. So in corn and beans, there are some premixes available. And mostly there there are some excellent options in corn. And those have already the residual herbicide like like, Metallachlor. And then also it also contains some, herbicide like, glyphosate or calisto in it.
Speaker 3:So it's a premix cocktail that has both residual as well as foliar active herbicides. And those premixes are excellent in this type of scenarios.
David Nicolai:There were some other comments in the crop news, and I don't know if I can bring in sit in or not but we were there was some mention about pH of soil in herbicides and some interactions and I know Tom it's different from west to east in Minnesota but especially in soybeans and we've got some products sometimes a concern on our more pH sensitive. Any comments on that things that our growers need to be aware of whether it's a pre or getting close to emergence?
Speaker 2:I think all of our growers need to be aware of the pH of their soils. And the reason for that is it may not be as much about this seasons weed control but it potentially could be the product carrying over to the next growing season. And I wish Citan was available, we should try a mic check again because Sinton did an excellent job in the article of comparing different products that worked one way at lower pHs and worked a different way at higher pHs. Siddan, are you there?
David Nicolai:I don't think that it's present time, but maybe there are some things if we have to bring this in. Deblin, do you want to probably provide some overview there too of some of those pH concerns?
Speaker 3:Yes. So again, I'll refer back to the process, how it happens. So we gave example of atrazine versus some sulfonylureas like ALS herbicides. So the atrazine in the low pH, it binds really tightly to the soil particles, and it is less available for weed control. But there is a less carryover risk.
Speaker 3:When it is high pH, it is more soluble and better weed control and better, higher carryover risk. So how it happens is atrazine takes some hydrogen, from the soil solutions, and it is positively charged, and it binds tightly to the soil particles in the acidic soil. However, in the alkaline soil, it is more available in the soil solutions. And we gave example of the sulfonylureas like classic or harmony that that has lower injury risk and lower activity in the so lower injury risk in the acidic soil. However, it breaks down slowly in the alkaline soil.
Speaker 3:So those are the example that we put in the in this crop news article.
David Nicolai:Well, we're reaching towards the end of our allotted time here in the podcast, but I wanted to check-in and see if my cohost has any other comments on there. He's been out busy planting soybeans this last week. So I know that's where his situation is in terms of that. But you know, you're gonna get on the weed control soon, aren't you?
Speaker 4:Oh, yeah. We're gonna be on it.
David Nicolai:Okay. There definitely we're going to be able to to do that. Well, soon we'll we'll turn to post emergence. But we I guess Tom I know years ago we have we've always talked about the factor of waiting for it to rain before I did or looks in the forecast but I think you've always taken the approach don't wait go ahead or would you just reemphasize that point I guess in terms of timing here?
Speaker 2:Well that's the way I have run my program and we'll even lightly incorporate if we don't see rain in the forecast. I like to tell growers we're not doing tillage, we're incorporating the herbicide so the techniques are different but Dave, I think we would be remiss if we didn't talk about what if it doesn't rain. How long are herbicides on the soil surface and what happens if it doesn't rain seven, ten, fourteen, maybe even twenty one days and I'm gonna start this and then I'd like Debalin to continue the discussion. So I mentioned ethafumisate. Ethafumisate tightly binds to soil.
Speaker 2:It's water insoluble so I'm not worried about ethafumosate blowing away or photo decomposing. What I am concerned about is getting it into the soil and we need a solid inch of rain to get ethyl into the soil. Some of our other products are more water soluble and I think we can get by with maybe a half an inch of rain for those products. Dublin, tell us about some of the other products and how long you're comfortable with them being on the surface before you worry about them starting to decompose.
Speaker 3:Yeah. So that's an excellent point, Tom, because if your herbicide we in extension term, we call it activated. If your herbicide is not activated and it is not actively controlling the weeds, yeah, I mean, it is very risky to have those herbicide on the soil surface because if they don't go to the soil solution, they there there will be quick photo degradation because of the sunlight. And I just pulled an article from Bob Hutchler from Iowa State, and he'll he put a list of herbicide for photo degradation with medium to low category. So some of the herbicides, like, I think, like, atrazine and metribuzent are in the lower category.
Speaker 3:And some of the herbicides like trifluraline and metrolaclor, those are in the medium category. So so that means, some of the herbicides will will be photo degraded, like, quickly than the other herbicides. And then sometimes we talk about reach back if you didn't get, you didn't get the rainfall within the first five, six days or ten days, and then you got a little bit rainfall and that kind of take those herbicide to the soil solutions and they're available for the weed control. That happens. But now think about the ten days that there will be a lot of weeds already up, and they will not be controlled.
Speaker 3:But but still the future weed control can happen with those reach back, with the solutions. And then another part is microbial degradation of the herbicides. With a lower rainfall, microbes are less active. If it is hot weather and lower rainfall, they are a little bit less active. That's a good side.
Speaker 3:But, again, with a, like, single flush of rain, the microbes will be super active, and they will actively degrade those herbicides with the warming warm temperature and a little bit of moisture. So, yes, I mean, if there is no rainfall, it is a loss for those herbicides. But, but still, like, I will not oppose spraying any pre emergence herbicide regardless the situation. I know sometimes it is wastage of some of the herbicides, but most of the time, I I saw in last few years, the spring is a little bit wet in wet in Minnesota. So we can probably we can probably, like, spray pre emergent herbicide and hope for the rain.
Speaker 3:If it will rain within the ten days, there is a high chance that herbicide will be activated.
David Nicolai:Yeah, again we're talking about the pre emerge herbicide article in the recent Minnesota, University of Minnesota Crop News under pre emergence herbicides. And last thing I wanted to point out here is some of our coworkers in other states in Wisconsin have pointed out recently some better long term success into looking at two way and sometimes three way mode of action pre emergence herbicides. And in particular maybe more on the corn and soybean regime but any comments about that? And then I think finally a lot of us in terms of growers are applying group 15 herbicides. Are we going to lengthen our ability to have that product out there in field for a longer period of time?
David Nicolai:So just last comments about that.
Speaker 2:Dublin, I'll go first on this one. In sugar beets we don't have a lot of options so we're primarily using group 15 herbicides for small seeded broadleaf like waterhemp control but we really try to educate our listeners, our growers that in the crop sequence with soybean, with corn, with small grains that they look at other families of herbicides. So try to introduce the diversity of different families in the rotation because we don't necessarily have that opportunity in sugar beet. Dublin?
Speaker 3:Yeah. So, for corn and soybeans, we have some options, available for rotating the sites of action or mixing, the sites of action. The main concerning news is, the resistance development, and, there are, like, lot of, like, target side, non target side resistance development. The main idea about controlling the weeds at current time is either rotating the sites of action or tank mixing multiple sites of action. That's why we are emphasizing that.
Speaker 3:Like, it's like your weeds are resistant to couple of the sites of action, but you are bringing the diversity in the sites of action in the herbicide, and you are attacking those weeds. And for the group 15, yes, my colleagues from other states like Illinois and other states, they confirmed the group 15 registered waterhemp and some Palmer amaranth already. Those are present. And I know that this thing is coming, and we should keep an eye on that. But, I mean, at this time, there is no new chemistry or new sites of action in in the market for corn, soybean, or sugar beet.
Speaker 3:So the best way is rotating or tank mixing so that you are not relying heavily on one chemistry and then your weeds are registered to that chemistry.
David Nicolai:You know, hence the probably the uptick in products that are are two way or or three way in some of these situation. But I think it all goes back to do you know your fields, do you know what weeds are in there and have a history in putting that together in terms of that. I think we've pretty much covered most of the articles and thereby know that my cohost here, Doctor. Nave, has a point or two you'd like to bring in.
Speaker 4:I just want to mention, we mentioned the Minnesota Crop News, and I believe probably everybody listening to this podcast probably subscribes already. But if not, I think the easiest way to find it is just Google University of Minnesota Extension or Minnesota Crop News Minnesota Extension or something like that. But if you include Minnesota Crop News in any Google search, you'll probably find it. The URL is a little bit long. It's blog-crop-news.extension.umn.edu.
Speaker 4:That's a whole bunch. So I think googling Minnesota Crop News will take you there. Now be sure and subscribe. Be sure to check-in on crop news. There's been a bunch of publications in the last week, so it's a good time.
Speaker 4:I know farmers are busy, but it's maybe some evenings or some crop advisors should take a look at those if they're not normally looking through the crop news.
David Nicolai:Very good. Thank you, Seth. Any last words, Tom or Deblin, on this subject matter? We'll be talking about post emergence weed control down the road here a little bit.
Speaker 2:Well I always like to encourage growers to stay safe, don't take any risks and if you have any questions, don't be afraid to get a hold of us. I'm speaking for Deblin, our contact information is out there. I don't mind taking calls day and night and on weekends. So please get a hold of us, me if you need us.
Speaker 3:Alright. So same same as Tom said, like, I'm also open to take any calls or emails. And, also, my suggestion from weed science standpoint would be try to be start clean and stay clean because, that's how you can, get ahead of the, planting season, ahead of the weeds, basically. Because, you know, if you start with not a clean field, then it is very hard to manage them using the post emergence herbicide. Even if you plan for two pass post emergence programs, still it's not enough for the the, you know, protecting your yield and control those weeds.
Speaker 3:So, yeah, my advice will be start clean and stay clean.
David Nicolai:Well, you both indicated that we've had an early start in planting and continuing to have that so keep in mind we can't sit back in the easy chair and rest in terms of weed science and weed control because with this warm temperatures the weeds will soon be following shortly behind there so it's important to be on them early rather than be behind in terms of control. So we'd like to thank again our guests for today's podcast Doctor. Tom Peters, University of Minnesota and NDSU Extension weed specialist in sugar beets and then also Doctor. Devlin Sarangi, University of Minnesota Extension weed scientist in corn and soybeans. My name is Dave Nickel.
David Nicolai:I'm here with my cohost Doctor. Seth Nave. We appreciate your listening in situations with this in terms of talking about agronomics and crops. So this is the University of Minnesota podcast, Minnesota CropCast. Thank you and have a good day.
Speaker 3:Thank you.
