Iron Deficiency Chlorosis: I'm Dreaming of a Green Soybean
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Matt Pfarr:We're here to have a discussion and answer any questions you have regarding iron deficiency chlorosis in soybean or IDC for shorthand. Questions can be entered in the Q and A box, which is located on the bottom toolbar on your Zoom screen. Use the chat function only if you're having technical issues, please. You can just hold your mouse cursor near the bottom of your screen and the toolbar will show up there if you aren't seeing it. And the other thing is, when you log off today, we'll have a quick survey.
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Matt Pfarr:We heartily thank these organizations for their funding support. I'm Matt Pfarr, a regional extension educator in crops management. And we also have two guests today. We have Doctor. Seth Nave, he's our extension soybean agronomist and professor of agronomy and plant genetics.
Matt Pfarr:And then we have Doctor. Dan Kaiser, He's our Extension Professor in Soils, Water and Climate, dealing with all things related to crop nutrition. With that, welcome again. Seth, would you kick us off please by just painting the picture of IDC symptomology? How do we ID and rate plants with IDC?
Matt Pfarr:Your thoughts please on what we've seen so far this year as well.
Seth Naeve:Sure, and I haven't, I'm not doing any IDC research this year, so I haven't been out in the region quite as much. I think what we're really talking about is focused a lot in Western Minnesota primarily, all the way from the South to the North, but the Western Portion Of Minnesota where we have higher pH soils that that predominate in in the landscape. But, of course, this year, we've had more IDC than than normal. So those areas that we consider to be, you know, IDC prone have have been probably sneaking to the east a little bit this year. So we're seeing more in some pockets the further and further east that we go, even in some areas that are a little bit unusual for this.
Seth Naeve:So Dan can talk about all the, you know, the chemistry involved, but I think from a symptomology perspective, we're just seeing some yellow soybeans out there and some generally in pockets where we have the kind of prairie pothole region and more field wide in in the Red River Valley. And this is we get this classic IDC symptomology, which is basically, you know, yellowing of the plant beginning about the V2 to V3 stage. So we have interveinal chlorosis, so it's basically yellowing of that soybean leaf between the veins, and the veins remain relatively green in all those new developing leaflets. And then as we move forward through the season, the soybeans either grow out of it or they just die completely depending on the severity of the the the issue that we've gotten that year.
Matt Pfarr:Dan, any follow ups on symptomology for IDC in soybean?
Dan Kaiser:Well, the main thing is just to not confuse it with anything else. Although, I mean, if you look at some of the other nutrient deficiencies, there aren't really a whole lot that I'd really expect that we'd see that would look like it. Since iron is immobile in the plant, I mean, the deficiency symptoms will show up in the upper leaves first. I mean, there's some other nutrients that can also do that. Mean, sulfur being one, although I just really haven't seen strong sulfur deficiencies here in Minnesota.
Dan Kaiser:I mean, if you're looking at deficiency symptoms, I mean, it pretty much fits with specific soil types and so it's a lot easier to figure out than some other things. Potassium is kind of another one too that sometimes later in the season you're going to see that. But, yeah, I mean, I mean, most people, I think if you you know your soils that are prone to it, and so it's it's something to kinda look out for. I mean, normally, it's gonna show up in the same spots more or less year after year. Last year, I think, was a little bit of a difference.
Dan Kaiser:So we had some reports of some some fields that hadn't seen IDC for a long time or hadn't that that where it was showing up in. So that's kind of the nice thing about it. I mean, like I said, it's it's kinda fits with certain soils and certain areas of the field, so it should be pretty easy. You shouldn't really confuse it with anything else.
Seth Naeve:Yes. I I'd only add that, you know, it's it's really there's a lot it's it's a water related issue, and it it depends on where, you know, the the the soil conditions and the and the the soil moisture capacity and and what what kind of the amount of water that we have in those soils and what what strata within the soils. And that seems to seems to be a big driver of IDC. And so I think that's part of why we have such different we've been seeing such variation year over year is that we just have some very different weather patterns. And so some years we have some you know, the timing of the heat and and the, rainfall interact with these soil conditions to really cause or diminish the the, the effect of IDC.
Seth Naeve:It it varies a lot by year.
Matt Pfarr:I just wanted to jump in here. I think this leads into another thought or question I had to prepare for you gentlemen, which is really about that environmental piece and why we see such variability year to year. So I've heard you gentlemen present on IDC in the past about what predictive climate variables, so your precip and your also your heat that you're getting in the season or your cool weather, nitrates in the soil. So I think before we jump into things that farmers can do proactively in their management, let's just think about all the things that make IDC better or worse year over year. And are they predictable at all?
Matt Pfarr:Could we, through research, how close have we gotten to saying, Hey, this year IDC is really going to be an issue, and we knew about it in May or June before it even showed up, or where are we at in that sort of progress? Seth, if you want to start on that.
Seth Naeve:Yeah, I think this is really Dan's, you know, area, but I I just think that, you know, I I do I'm a believer in this in this this kind of this idea, and I think Dan can have you know, put some more science behind it. But, you know, this this where we have where we have root exploration in the soil, there's plenty of there's plenty of iron available. We just don't have the iron in the right form. And then we've got, you know, we have these interactive factors, salts and calcium carbonates and nitrates that are carried by the water, and where those are within the soil strata and where the roots are penetrating in the soil all interact to kind of give us this, you know, this variation that we have year over year. And so I think, you know, Dan can go into bicarbonates and and all the all of those cycles.
Seth Naeve:I think that would be helpful for for the audience. But I think that's part of the complexity is we've got a number of factors that are all interactive, and they all interact with with water at some point within this cycle.
Dan Kaiser:Yeah, and that's a difficult thing because a lot of our issues with IDC are related to bicarbonate in the soil, which isn't stable. We can't measure it. If you look at how transient some of that is where some of the issues come and go, it's really hard even to know beforehand. If you could give us a good measure, what it would really mean. I've tried to look at some of the factors and run what we call multiple regression.
Dan Kaiser:Essentially what it is, take a bunch of factors, you throw them together and you try to develop a model based on multiple factors to try to predict the severity of IDC. The issue is backward looking at it, it's a lot easier to predict and get a nice relationship using any sort of equation anybody or any sort of thing that looking at all these factors that anybody's developed, it never works to forward predict it. That's kind of the issue. It's such an interactive issue. You can have the soil conditions that would favor it, yet you don't always see it.
Dan Kaiser:And that's kind of the problem with it in terms of predictability. That's why looking at the issue and looking at management strategies, why something like a tolerant variety works just more as an insurance policy in those areas, just try to at least hedge your bets against having IDC since we can't predict it. I mean, it'd be a lot easier if you could just go out and treat it and once you see it, but that doesn't always work either. So it's one of those things that you really have to make the decision almost ahead of time. It's really the best option you have.
Dan Kaiser:And, you know, then hopefully, you know, it'll flare during a year. It won't be severe enough where you'll actually get something out of those field areas. But, think, Seth, if we could answer the question just simply by measurements, we probably wouldn't be talking here today about it. I mean, we'd have this all figured out. It's a complicated factor when it comes to soil.
Dan Kaiser:Then looking at me on the genetic side too, it's a complicated factor and you're looking at the genes associated with it because it isn't, I think, necessarily one thing. It becomes a really a bigger issue that keeps somebody like me employed for the longer term and the geneticists too looking at it.
Seth Naeve:Yeah. Just to round this out, let's talk about the genetics really quick, and then we can go on to some of the management topics. I think since Dan brought it up, it's an important one because there's all these factors involved in the soil, the plant is also dealing with iron by multiple mechanisms. There's uptake mechanisms. There's transport mechanisms, and then there's there's a lot of mechanisms within the leaf to deal with both the nitrate and and the iron within the leaf.
Seth Naeve:And so those are all different genetic pathways that are followed. So the geneticists and breeders, they know really well that there are some really important genes. And when those aren't around, we have really, really yellow plants that are highly sensitive. But reverse engineering this to go the other direction is really hard because we have to put all of them together. So they can find lots of genetic associations with IDC across multiple chromosomes, but pairing them all up and putting them all together in order to make these really tolerant lines has proven to be really, really challenging.
Seth Naeve:And I guess just to kick the horse a little bit more, this is probably the reason why we deal with this problem in the North so often is that every one of these new genetic traits, new herbicide resistance packages comes out from the companies, and those are all introgressed into more southern genetics first and then moved into a backcross into our populations. And so it's, we have to kinda start over in many ways every time we get a new set of set of genetics come into our region. And so the breeders from those companies have to work really hard to get all these complemented genes put back together, assembled back together, and and have and have good soybeans again. That's why we if you look at a chart of every every new variety that comes out, we we seem to flare up with some IDC for the first year or two just just because of this, this kind of lag in breeding for some of those things. And because, frankly, the corn belt really narrows up as we get, shorter than, you know, group one, one and a half maturities.
Seth Naeve:We really have a narrow width, and so the companies just don't have the have the the the bandwidth to to do all the breeding that they do in groups three three and two soybeans.
Matt Pfarr:Seth, if we could stay with that genetics topic just a few more minutes, as we're on it. I've heard you present on this rank order of agronomic priorities to deal with IDC proactively. So we've already discussed that IDC is something we can't predict ahead of time. So it's not out of the question for us to sit here today in July and plan for success next year in 2026. So it's like, what are we learning this year?
Matt Pfarr:Maybe we'll see some varieties of soybean that are doing well in fields that are traditionally hot for IDC for some growers. Is that going to be durable year over year? Like what choices can we make in those genetics? And do you still feel that that's the number one priority for every acre across the farm for growers to be selective about which genetics they're placing on?
Seth Naeve:Yeah, I think to back up just a little bit on the genetic side, and I think Dan would probably agree, he's done a lot of the same work that I have, is when we look at varieties, there's really very little downside of choosing the absolute best variety for IDC if you're in an area with high pH soils. So they don't there's no additional cost. There's no trade involved with IDC tolerant varieties. They tend to yield equally well as as other varieties, and so there's no real downside. The challenge I think that farmers have with choosing soybean varieties is that there's we're really in a short cycle in terms of variety release and and how long those varieties are in the marketplace, and farmers are really eager to get the newest varieties.
Seth Naeve:You know? And I've been picking on the new traits, but, of course, that's always an issue as farmers want newer traits or a different trait. So the challenge with this is they they may be shopping for our varieties that they don't have a lot of history with. And so the one easy thing that farmers can do is choose varieties that have for those fields that are a little bit hotter for IDC, choose the varieties that have been proven for them, that they've seen that they perform well, and utilize those in those hotter fields first, and then probably prioritize some newer varieties that they don't have as much experience with in some of those fields that maybe don't have as much of a history. And that's I think that's an easy way to start this whole discussion because there's very little downside risk of doing that, and it and it positions the farmer in in really a better a better spot for dealing with a potential year where we do have IDC.
Seth Naeve:And I I guess the other part of this that I didn't mention is because we don't see IDC really heavy every year, farmers may have to dig back in their memory a little bit or look back a little bit further to consider some of those varieties that have done really well for them. And then ultimately, they're gonna have to trust their seed dealer on some of these things too. But these ratings don't always follow through with these newly released varieties because they haven't been tested in enough environments.
Matt Pfarr:Excellent. Let's shift gears from genetics to fertilizers, Dan. I think this is a really a topic rich environment because we know nitrates can actually make IDC worse in the soil. We know that there are iron chelate fertilizers on the market that are applied to, to give a little bit of easily available iron in theory to the crop. Maybe there's people wondering, hey, can I go out this time of year?
Matt Pfarr:I've seen IDC flashing, I'm sick of looking at that. Is there an easy fix I can stick on this even though it might cost me a little bit of an investment upfront? Where do you want to start on that, Dan?
Dan Kaiser:Well, I think we could just talk a little on the nitrate side because it is an issue. We know that just looking at some of the data that soybean plants, they take up too much nitrate, it can cause problems in terms of either internally in the plant or externally as nitrates being taken up with making IDCs little bit more severe. Now the issue really is, the areas that are prone to IEC, they tend to be areas of higher organic matter that would likely mineralize more nitrogen. I don't know how much you really can do on that. We say minimize the amount of excess nitrogen that's being carried over as much as possible, but there's really only so much you can do there.
Dan Kaiser:I don't know really what for management wise really that we really can do other than just getting a variety, I guess, there like Seth was talking before that's more tolerant. The fertilizers, really there are limited options. You know, when I first started, that's kinda when soy green was first being put onto the market, which is it's the chelates, I mean, really are important with iron because when it comes to chelates, when you look at any metals, zinc, iron, any other metals you're trying to apply to a crop, there are specific chelates that are more successful at maintaining the concentration or maintaining the availability of the central metal ion. With a chelate, essentially what you have, chelate means it's Latin for claw and what it is essentially is a molecule that'll surround a central metal ion protected from being released into the soil where then it can react with other nutrients and form compounds of various solubilities. So it's really important with iron that we start looking at the products out there like soy green, which is an ortho, ortho EDDHA.
Dan Kaiser:There are some different what we call isomers or different. It's just kind of how the, if you kind of you know, think of the the chelate, like, as your hand kinda just the arrangement of the the ligands or the parts of the chelate that surround the the ion. And it's important, because if you're looking at sources, I mean, there's you can get DTPA. You can get EDTA. You can do different iron chelates, and they aren't gonna be effective.
Dan Kaiser:They don't really maintain the availability for a long enough period of time. I mean, and the issue with EDDHA always was cost. It was tested. There's I've got data. I've dug back into some of George Reams' work back to around 1980 where they've tested EDDHA.
Dan Kaiser:It just never was economically viable until, the company that, you know, sold it to West Central is buying it through, came up with a, viable way to to make it. You know, for a while, that was really the best option. The big thing that you have to watch out for if you're buying like an EDDHA is just looking at how much of it's in the ortho ortho form because there are other products out there that have various concentrations and they'll work as long as you put enough on. That's kind of the key with it. There is a newer product.
Dan Kaiser:I think it's the EDDHSA or something like that. That's, that's been, I know Jay Goose before he retired tested that he found, that had some some decent efficacy similar to EDDHA. So, I mean, that's really the main thing with it is you just have to make sure you have the right chelate form. You know, looking at application timing, you know, Matt, you mentioned coming in, if you start seeing flash, can you apply it? I mean, we've been able to green plants up with it with a foliar application.
Dan Kaiser:That's one of the things with chelates, you can get some leaf penetration with it. We'll green it up. The big thing with iron being that the nutrient is immobile in the plant really is when you do apply it, it's whether or not it's getting translocated, which technically it shouldn't. So that means if you have a problem that persists, you might be able to green the plant up what you're spraying it on, but it with new growth, if it still persists, you may get yellowing with new growth. So that's always been the problem within season applications with it historically.
Dan Kaiser:It's just been the fact that, you know, you look at the data, you almost have to apply it before the problem persists and then you may have to make multiple applications. So that's kind of the main thing with a lot of treatment right now is whether or not it's going to be just cosmetic. I mean, really the big thing I look at, I mean, the plants are turning yellow, as long as they're not getting severely stunted. Normally if there is a yield loss, it's relatively minor. I've seen that when we've looked at severity ratings in fields, when I've tested tolerant and susceptible varieties, you know, we can see if the plants are kind of just normal size compared to the rest of the field.
Dan Kaiser:If they're just a little yellow, I mean, really there hasn't been as big of an issue. It's really kind of when we start seeing stunning, which is the problem. If it is that severe, I just don't know if you're going to be able to correct it with just a single application. I mean, you're just gonna have to look at multiple applications over time, which it'll start to get expensive because that's one thing a lot of these key lights, they are not cheap. So that's why it's really best to have it near the roots where the plant can continually feed off it.
Matt Pfarr:I wanted to, Seth, feel free to jump in here as well. But with my farmer cap on, we've talked about making a proactive plan for iron deficiency chlorosis. So you mentioned cost, Dan, of these fertilizers and probably maybe more effectiveness in a hot part of the farm. Or if you're up in the Red River Valley, and you have that La Cruz Stream soil of one to two inches grade change across a whole section of farm, you know, that might be an every acre type deal. So I know we were dealing with people in the North, the Central, the South Of Minnesota have very different experiences with IDC on their soybean and all the different soil types and climate we have in the state.
Matt Pfarr:But some research that you have from those different parts, if you guys want to share, you know, we can't really go through an IDC webinar without mentioning Doctor. Jay Goose at NDSU and the decades of work that he put against this problem as well. But he would always say, you know, there is there is a place for iron chelate fertilizer likely in the upfront of the the crop. Now, I know we don't know how severe the problem is going to be, but we tend to generally know basis on those low flats or those eroded knobs, Doctor. Goose would always talk about where we're going to have IDC some of these farms, unless it's, you know, in the Red River Valley where we might have, Edro to Edro issues with it.
Matt Pfarr:So what's the ROI guys, I guess, to boil that down and do a shorter question?
Seth Naeve:Well, let me jump in real quick. I my my I guess my overview on this is that varieties, increased populations, and iron chelates all work, and they all pay when we have IDC. So there's no question, and it seems like our work shows that those things are pretty much additive, so you can get benefit from each one of those things. Obviously, as I mentioned earlier, the variety is the cheapest and probably the biggest hammer out there, and so then increased populations helps a little bit. And the iron chelates work when we have IDC and they pay.
Seth Naeve:So there's no question. So the question I think is what is the frequency of IDC on any particular acre? And if farmers know they're gonna have IDC every other year or 50 of the years or three quarters of the year or, you know, one quarter of the year, then they can make that judgment about whether they should apply that on that particular acre. And this is you know, this is this really this technology really lends itself to variable rating both from a population standpoint and from from an application of iron chelates. And farmers have maps now.
Seth Naeve:And we've got we've got remote sense maps. We've got yield maps. We've got a number of different options for farmers to keep track of those locations. And I think there's an opportunity for farmers just to to look back in their datasets, either using some online tools that they might have or their own data and their own yield maps. They can relate to IDC, and they can do a pretty good job identifying where and the frequency of those spots.
Seth Naeve:I think that's the place to start in my mind.
Matt Pfarr:Dan, I'd like to have your thought, and then we'll go for questions here to finish out.
Dan Kaiser:So, you know, it's interesting. I mean, looking at it now, I've done a most of the work that I usually do, we we try to do a a highly tolerant and susceptible. I mean, Seth, I think does same thing when we look at testing a lot of these different strategies. Really the challenge, as Seth said, is you're making a decision upfront based on the severity. You're looking at varieties, you may be looking at variety just more on the yield side and if you get a susceptible in there, meaning they get really hammered, then you have a problem.
Dan Kaiser:One of the things with a lot of these management strategies I've seen, and I think Seth, you've seen the same thing. If you look at iron chelates, we we do get a good response with the susceptibles. I mean, if you look at it actually, I get more of a yield return with a susceptible variety with the chelate than I do with the tolerant. I mean, the issue is though I never gonna ever get the same actual yield level with the susceptible that's treated versus what I could do with the tolerant and untreated. That's one of the things I think that really the problem for most of Central Western Minnesota outside of maybe Yellow Medicine County, few areas around there where they have some of those edge road edge road issues is, you know, variable seeding, tolerant variety, some of the really the the more susceptible areas and a less tolerant in some of the other areas where you might be able to get a little bit of a for and boost for yield.
Dan Kaiser:I think it's it's probably something that when I look at a lot of our data supports, the data supports it. And that's kind of been the big thing. It's we've always been focused on is can I just take some of these really high yielding varieties that are less susceptible and treat them and get the same yield or better yield, and I never been able to do that? We've looked at the oat companion crops, that does work. We've seen that where, you know, having the oat as long as you can get it killed in time that will work.
Dan Kaiser:I haven't had much with the seeding. I know Seth's done more work seeding rates than I have. And then the the bigger challenge I have had with chelates has been, you know, I struggled for years getting a decent response in fields. What I did tend to find is the other issue that tends to pop up in these areas that we never talked about is, is soybean cyst nematode in some of these same areas. And, you know, you get to that situation where, you get a high cyst count in some of these spots and I've always wondered, like, why am I not getting a good response to my iron chelates?
Dan Kaiser:And I, you know, pull cyst counts where I've got 15,000 eggs, you know, the egg counts that are are extremely high and you you start to see issues where I'm hammered on that end, which it gets to be more complex with the with that that issue. So it's just something to think about. I mean, you know, I just kinda stress. I mean, really, the tolerant variety is the best option for the most part. At least it gives you that insurance, hopefully, that you'll get something.
Dan Kaiser:I mean, you know, there's some areas that are might get completely hammered where the tolerant might not be good, it's still the best option, I think, for most growers to consider. These other things, you know, if you have the option for in furrow, I mean, could do it, but, you know, it just keeps getting more expensive on a per acre basis. And, you know, with tolerant, it seems like I gain more with tolerant variety than anything else, when managing, you know, especially managing risk.
Matt Pfarr:Perfect, perfect. That could be prescriptive. Now we had a question come in that I think we have just thirty seconds to address, and that was about wheat in a corn soy rotation. Is it profitable? And I think we can kind of mold that discussion on IDC and just say that, you know, wheat and corn in a cheeky way are tolerant varieties to IDC because grass species, when they get iron, they secrete what we call Phytosiderophore, sort of like a biological chelate that is actively helping those plants get iron.
Matt Pfarr:That's why we don't see the grass species suffer from IDC in the same place as we see soybean, because soybeans trying to secrete acidity into the environment, but it's very much neutralized by that baking soda, that calcium carbonate that's there. If anyone's ever used that to clean up a chemical spill, a little arm and hammer, you know what I'm talking about. So that's why more soybeans is to Seth's point can help themselves. So long story short, Seth, adding weed in in a hot IDC field, is that gonna be beneficial to the rotation? Is it profitable?
Seth Naeve:Yeah. Spring wheat, I think I think there's an opportunity mostly to stretch out the soybean cycle or just the soybeans are gonna benefit by more years out for part of the reasons that Dan mentioned, SCN and other problems. So the we didn't get to that point, but I think that's the other issue as multiple stresses reduce soybeans' ability to deal with IDC. So, you know, reducing disease pressure by extending the rotation is gonna be helpful. I'll flip this a little bit further maybe to the academic point here and and say, you know, the idea maybe about winter wheat in the South or something like this gives us a whole another option to deal with this a little bit differently.
Seth Naeve:You know, we could we could plant soybeans, you know, potentially figure out a way to do a real short cycle after after wheat. You know, if we had enough water, we could potentially do it in some cases. For winter wheat, you know, there's an opportunity for soybeans before a winter wheat crop too. So spring wheat, I don't know that it offers us much beyond corn corn soybean rotation, I guess, is probably my my final on that thought.
Matt Pfarr:Excellent. A lot of great points this morning. Let's bring this to a close. We don't have any other questions coming in. Thank you, Seth.
Matt Pfarr:Thank you, Dan, for joining us quick this morning. We'll have future field note sessions coming up in the following weeks. I'll mention that again in a little bit. Thank you for all the attendees that came here today for our University of Minnesota Extension FieldNotes program. This program is made possible by our sponsors, the Minnesota Soybean Research and Promotion Council, as well as the Minnesota Corn Research and Promotion Council.
Matt Pfarr:When you log off today, there'll be a quick survey, please take just a minute or two to fill that out. Next week's topic on July 9 is still being ironed out, but will encompass discussion around timely topics like drown out areas and fields potentially. The official topic will be posted in the email invitation for July 9. Then on July 16, we will have Ryan Miller hosting a field notes session titled, Reflecting on Weed Control Successes and Failures in 2025, Weed Escapes Management and Planning for Next Year. So again, thank you.
Matt Pfarr:Have a great rest of the day, a wonderful Independence Day, and we'll see you all next week.
