Corn updates and crop disease considerations
I'm Ryan Miller, Crops Extension Educator. Earlier this morning, we recorded an episode of the Strategic Farming Field Notes program. Strategic farming field notes is a weekly program addressing current crop production topics. A live webinar is hosted at 8 AM on Wednesdays throughout the cropping season. During the live webinar, participants can join in the discussion and get questions answered.
Ryan Miller:An audio recording of the live program is released following the webinar via podcast platforms. Thanks. And remember to tune in weekly for a discussion on current cropping and crop management topics.
Claire LaCanne:Again, welcome to today's Strategic Farming Field Notes program from University of Minnesota Extension. These sessions are brought to you by, of course, University of Minnesota Extension and generous support from farm families in Minnesota through the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council. We're happy you've joined us for today's session focused on, corn updates and disease management, updates and considerations. My name is Claire LaCanne, extension educator in crops, stationed out of our Andover regional office. And we welcome Jeff Coulter, our extension corn agronomist, and Dean Malvick, our extension plant pathologist.
Claire LaCanne:I'll hand it over to Jeff first to just ask you, Jeff, to give us an overview of corn conditions and what you're seeing out there. Just kind of give us a growing season update, if you will.
Jeff Coulter:Sure. Well, good morning, everyone. Yeah. As we know, this has been a really challenging growing season, especially with the tough planting conditions that required, quite a bit of replanting, and then all of the rain that we've had. And, you know, the crops have looked quite rough this year.
Jeff Coulter:In some places in Southern Minnesota, farmers have told me it's been the worst crop that they've seen in their lifetime, basically. So it's been challenging. Now summer has came on, you know, we've got some heat and, it's dried up a little bit in some areas, and the corn is starting to grow more rapidly. Corn is picking up some better color, at least the corn that hasn't been experiencing excessive water. And, you know, right now, some of the corn's soaking.
Jeff Coulter:According to the crop report that came out on Monday, about I think it was, like, 16% of the crop is soaking across the state. That's about 5 days behind last year and 2 days behind the 5 year average. So we're a little bit behind normal, and there's a lot of variability in the crop, within fields and between fields. So, we're kinda dealing with that this year. Initially, the prediction was for more than normal growing degree day with growing degree days, to accumulate during this cropping season.
Jeff Coulter:But, so far, that doesn't really seem to be the case, and it seems like we're just a little bit behind normal. But we should be able to catch up, quite easily if we get, you know, a week of warm weather or week or 2 warm weather. So, right now, you know, the corn is in that critical period, and the critical period for yield determination generally begins about 10 to 12 days before the tassels emerges emerge and lasts for about 3 weeks after the tassels emerge. So, right now, we wanna have, you know, good temperatures like we have now, where it's warm but not excessively hot. We wanna have sufficient soil moisture.
Jeff Coulter:We wanna avoid having drought conditions. So we've pretty much got those bases covered for ideal temperature and soil moisture conditions in a lot of places. If it does if corn is experiencing drought conditions at this time of year right before the tassels come out, that can slow the, emergence of the silks, but it can result in normal or perhaps earlier than normal release of the pollen. So that can disrupt the timing between the pollen shed and the silk emergence and kind of affect the quality of, fertilization. And that's generally not very common in Minnesota.
Jeff Coulter:We don't see that very much. What we typically see in Minnesota is that pollination occurs successfully, but some of the kernels that are established typically end up drying up drying out, withering, and just, being lost mainly at the tips of the ear. And that's a that's a result of typically, drought stress, following the, successful pollination. So for that, you know, it's that end of end of July and the 1st part of August are really important for, trying to avoid that. So, you know, right now, it's just been kind of a tough year, and, people have been trying to decide if they should put on supplemental nitrogen on some of this corn, if it's worth it.
Jeff Coulter:But there's so many other factors on some of this corn that's been, affected by so much water. You know, in some cases, it's just really short. It's just experienced so much water, and people are wondering if, extra end to that small corn will even be worth it. Just because there's so many other factors besides nitrogen deficiency that is, affecting the yield potential of that crop. So we're kinda moving beyond that now.
Jeff Coulter:Generally, we wanna have our supplemental and applied before tasseling, and and generally earlier than that. Typically, I would say no no later than about the b 14 stage. So we're kinda moving beyond that time now, and we're moving, more into the, the reproductive phase of the crop. And, you know, so far the temperatures right now this week and the extended forecast look good, for minimizing stress on the crops. So, I guess that's kinda where we're at in terms of the growing season.
Claire LaCanne:Thanks, Jeff. Yeah. Do you is there anything, I I don't know, useful to talk about right now as far as, like, really uneven stands? I we know that'll be something we'll think about during harvest, but anything now, to comment on there. I'm, you know, my family's farm is in southern Minnesota and we're talking some some corn that's tall and tasseling and in the same field, pretty large stretches of like ankle high corn, you know, in some cases.
Claire LaCanne:So anything there to talk about as far as, like, just extremely variable fields?
Jeff Coulter:Yeah. You know, like you say, that tall corn that's tasseling that has that nice dark green color, that's probably gonna have, you know, near maximum yield potential. Whereas that corn that's, you know, ankle high, knee high, just really stunted, it's probably not even gonna produce an ear. If it does, the ear is probably not gonna have much, if any, harvestable grain on it. So, you know, that corn that's really stunted out there is probably not going to produce much of anything, while the big corn is probably gonna yield close to normal.
Jeff Coulter:So it's, really variable and, you know, that could affect some things like harvest moisture, for some of this corn. The big corn, it's gonna mature normal and, dry down normal. But the if there's corn that's behind that still produces an ear with harvestable grain, that grain could be wet. So, that could be something to think about as we move forward.
Claire LaCanne:Yeah. So probably expecting in those fields not only, you know, height variability, but like of course possibly extreme like moisture variability of, of the grain too. So maybe a little preemptive to talk about harvest, but something to kind of think about as we progress in the season, I guess, is how how you're going to manage that and address that. Yeah. Any any other thoughts, Jeff, on the current weather conditions?
Claire LaCanne:Otherwise we did have a question come in from email about, you know, pointers for how growers might adapt to changing climate and extreme weather conditions. And if there's anything we can really do, to think about preparing for that and kind of manage for those changes.
Jeff Coulter:Yeah. And if I remember right, I think that question had to do mainly with hybrid selection.
Claire LaCanne:Yeah. That would yeah.
Jeff Coulter:Yeah. So
Claire LaCanne:getting good.
Jeff Coulter:You know, if we're thinking just on plain on agronomics, you know, one could think about a lot about nitrogen management and what they're doing for, you know, weed control, using a preemergence herbicide, that type of thing. But, that question was that was on the email was specifically asking about hybrid selection. And there's some things we can do, but to some degree, a lot of what we're doing already is, kinda the best case scenario, in a lot of situations. But, you know, if we think back to this growing season, some of that early planted corn did the best. But at the same time, that early planted corn had to undergo a few nights of, very cold conditions where the soil temperature got quite low.
Jeff Coulter:So thinking about things like cold tolerance, stress tolerance, At the same time, some of that corn that was planted a little later experienced quite a bit of crusting issues. So again, like, things like stress tolerance ratings would be important. In addition, you know, if one plants early, choosing a longer maturity hybrid that can take advantage of the full season, is one option, and it seems like a lot of farmers are doing that now as the relative maturities have slowly crept up, the relative maturities that the farmers are planting. But at the same time, you know, if one is on very fine textured, poorly drained soils, and, thinks that they have the potential of, you know, getting that planting delayed, then choosing excessively long relative maturity hybrids may not be the optimal scenario because then if you get any delay in planting, then you're already kinda towards, the later end of your planting window for getting that later relative maturity hybrid matured prior to the freeze in the fall. Another thing that one could think about, you know, is if if you sense that drought is gonna be an issue, you know, you could use drought tolerant hybrids.
Jeff Coulter:In general, the drought tolerance across the industry has increased dramatically. You know, these hybrids are being tested at multiple on farm sites before they're being released. And so they're they're experiencing the weather that's, you know, happened in the last, few years, and and they're just being naturally selected to perform well under those conditions. Alternatively, you know, if one expects late season drought, one could plant an could plant early and could also use early relative maturity hybrids to basically complete, the pollination and the kernel set period prior to the onset of drought. You know, that's an option.
Jeff Coulter:We've also seen recently in the news that there's was the strong winds or a duration that went through, Northern Illinois and, Iowa, parts of Wisconsin. And, in those scenarios, things like short statured corn may be a good option, to try to avoid, stock damage from that. So there's a few things we can do, but to some degree, it's really hard to predict, these, weather events. And, you know, the hybrids that we're using in general are being tested at multiple sites and under, you know, recent weather conditions, and they're just over time getting better and better.
Claire LaCanne:Yeah. Yeah. Thanks. Good suggestions overall. Like you said, it's hard to predict, but some considerations if we're kinda seeing maybe some patterns in in the weather and that.
Claire LaCanne:So thanks, Jeff. And I think we'll kind of transition now to to Dean, talking about diseases and what you're maybe seeing out there or possibly expecting with some of the extremely wet conditions. Dean, although that we're not experiencing wet conditions in every part of the state. So maybe you can comment on that too. But I think we'll segue first by talking about tar spot on corn, kind of stay on the corn topic.
Claire LaCanne:We had some emails come in asking about tar spot in particular, wondering if there's areas where tar spot is present now, and is it spreading? What is the kind of current distribution? What's the playing field like?
Dean Malvick:Yeah. Good. Good morning, everyone. So before I talk about tar spot, I wanna talk about what's what's out there right now as far as I know. I mean, everybody is seeing different things, I suspect.
Dean Malvick:But in terms of diseases, common rust is seems to be pretty widespread. And, now that's a low risk disease, but, nonetheless, it's out there. And, you know, at first glance, from a distance, it could even be confused with tar spot until you look a little closer. So just keep that in mind. Disease could be increasing, you know, with the relatively cool weather we have now and looking in the next week, you know, mainly in the 70s in in large parts of the state.
Dean Malvick:So but we may see more of that, but, again, that's a liver disease. That's common rust. Well, keep in mind there's another rust called southern rust. That is a much higher risk disease. I've not seen it in Minnesota yet.
Dean Malvick:We usually see that come up a little later, but will be something to watch for a little later. And and keep in mind that not all rust diseases are at risk. So tar spot of corn, as as Claire mentioned, you know, that's certainly a a big concern on the top of many folks' mind. And, where is it now? There is a national website that keeps track of confirmed locations.
Dean Malvick:It's called the corn IPM pipe. So that that is available in in the chat here, and it's easy to find on on a Google search or or other search as well. And so you can look at that, but just to give you an idea of where it is relative to us here in Minnesota, it's still located only in the southern 2 thirds of Iowa. It has been found in the northern third yet, at least not confirmed or reported. Not been found in South Dakota.
Dean Malvick:It's only been found in a few counties in Wisconsin. You know, 2 of those are roughly south of Madison, and 2 of those are much closer to Minnesota. 1 is right along the Mississippi River, and one is probably over somewhere around Eau Claire. I didn't look exactly where it is, but central east central Wisconsin west central Wisconsin. Excuse me.
Dean Malvick:So it is starting to develop in more and more places, and I expect it will, but map will increase quite quite a lot in the next few weeks, since this is a disease that typically develops later in the season. And, again, not found in Minnesota. I wouldn't be surprised if it's out there in a field here and there if we we look closely and at the right time. But so far, no confirmations in Minnesota. And, but I would say that it is a good time to start scouting to figure out where it might be developing.
Dean Malvick:And just just a reminder in terms of fungicide sprays for that, the optimal timing is is still seems to be r 1, r 2, typically, with with rare exceptions if it's really developing at high levels earlier. But, again, the disease tends to develop at later at higher levels, and that's when the biggest risk is. And we can run out of protective power cure to power those fungicides if we apply too early. So those are my comments about that. One last thing, you know, there are certainly other disease risks with these kinds of wet weather conditions and cooler conditions such as northern coral leaf blight, that is something to watch for.
Dean Malvick:I'm hearing reports of that around the region, not Minnesota, but it's something to watch for. And we know in times in the past, that's been a a significant problem in some fields. And just a few comments about soybean diseases. Now we talked about some of this in newsletters and blogs and other things. You know, the wet weather has been very favorable for root rots up to this point.
Dean Malvick:Phytophthora in particular, we've had excellent conditions for phytophthora in many fields, and we're seeing reports of significant damage in fields scattered here and there. And I just wanna note that we've, you know, recently heard a report of a field with a variety with both genes, rps 1k and 3a failing, which are the 2 genes that have been most widely effective based on history. And then 3a looking forward, you know, recent surveys suggest that that gene should be effective in most fields. But we are sealing that gene now fail in more and more fields too. Although we don't have a handle on how widespread that risk is.
Dean Malvick:But keep that in mind. And if you're having a problem with Phytophthora, You know, take note of which resistance gene you have in that variety and see if it's something you might wanna consider changing your attitude next year, another time. Rhizoctonia, retinal stem rot, certainly has been common too. You know, we're past the stage where most of that damage occurs to soybean, but nonetheless, it's still causing some damage, and and it can also be easily confused with Phytophthora thymus. So keep that in mind.
Dean Malvick:We also see a fair amount of bacterial blight, trivial disease, but it's it's out there and often easy to see, and typically in the top parts of the plants. And in the lower parts of the plant, septoria brownstock, so very easy to find. Usually not significant at all, the same for bacterial blight, but you may see it. And if it becomes high levels, then something to pay attention to, but it rarely does in soda. And the other couple things I'll mention is certainly white mold.
Dean Malvick:We've had ideal conditions for the early setup of the fields for white mold. And now that we're into flowering and the rows are starting to fill in many fields, now the risk is increasing substantially. And with the cool weather again we have, looking in the next week or at least for the next week, you know, seventies in the day, parts of the state, sixties at night. Lots to do, I suspect in many places, ideal conditions for it. So something to watch for.
Dean Malvick:And if you're considering fungicide applications, now this, you know, early R2 stage where the rows are filling is probably a very good time to put fungicides on. The other thing Dean, oh,
Claire LaCanne:I just wanna add in there that Yeah. Somebody put in the q and a, asking if there's a likelihood of sclerotinia this year so that would be white mold. And, you mentioned the timing for fungicides. Is there anything that people should be really mindful of looking out for or areas that they should prioritize scouting, anything like that?
Dean Malvick:Well, that's that's a good question. I I think a lot of folks know the areas that they that are post at risk. They've seen it in the past, and they they don't forget that. Right? Yeah.
Dean Malvick:I mean, it's it's typically more common in lower areas, but if it's wet, it can be a problem anywhere. Now protected fields low protected fields are highest at risk, but it can be anywhere if the weather conditions are late. And what else? Moving forward, frog eye leaf spot, that's a relatively new disease that's been developing in Minnesota in the past 10 years. We haven't seen much in the last 2 because of dry weather.
Dean Malvick:Again, we've had ideal conditions for that. That's a leaf disease with these, rounder spots, darker margins. And then the other one I'll just mention is we've had really good conditions set up to plants for infection and development of sudden death syndrome. So we usually don't see the symptoms in July, but as we get into, you know, the last week of July, early August, that'd be something to watch for as well. And those are my summary comments for right now.
Claire LaCanne:Yeah. So, kind of ideal conditions for a lot of diseases, it sounds like, unfortunately. Kind of a question that came in via email that's maybe more more general is just looking at fungicide applications on corn. Does it pay to do fungicide applications, and when does it pay? And I know that'll vary by disease, but
Dean Malvick:That's a big question. Yeah. Complicated one. I I think we can look at fungicide applications 2 ways. 1, right, targeting them to a disease that you know is developing, such as tar spot.
Dean Malvick:And they they can definitely pay if they're put on at the right time, and the disease develops to a level that causes you loss. Now the bigger question is how often do they pay when they're put on preventively or as a yield enhancement tool? I think our data here at the Minnesota would say, and and Jeff has done some of these trials as well, probably not very often if they're just applied generally. By far, you know, the greatest benefit from those is when we have a disease that we need to manage. There are times people report benefits in lieu of any significant disease observable, But that that's kind of hard to predict, and we think, generally, the odds of return are are low unless we have a lot of disease.
Claire LaCanne:And that's true for corn and soybeans. Right? I mean, yeah, just saying in general. Yeah.
Dean Malvick:Yeah.
Claire LaCanne:Yeah. I guess going back just a little to address another question that came in in email is about white mold and wondering if you should see it in soybeans or maybe could see it in soybeans, if they were planted into a thick mat of winter rye. So asking a little bit about the interaction with cover crops there.
Dean Malvick:Yeah. The cover crops can have benefits in a in a few different ways, actually, by re they it can help manage white mold, a few ways. It can actually shade the crop or soil early. It might stimulate the fungus to grow and sporulate before the soybeans are really susceptible. There's some ideas that that might be happening.
Dean Malvick:And the other thing is if we have a really thick layer of of residue on the surface, again, it can stimulate germination at at times if there's enough light getting through. Or if there's if it's so thick, it can actually inhibit germination of the structures, those little apothecia mushroom like structures that develop on the top of the the soil. It can inhibit developing those or it can actually inhibit spread of the spores from those. So there are several possible ways if there's enough of the residue, so that they could now whether we see benefits on a wide scale, I think that would be something we need more studies of.
Claire LaCanne:Yeah. And anything about cover crops in general that you wanna talk about, Dean, as far as a question came in on the email wondering if cover crops help break disease cycles. And we know that's a kind of complicated topic. But
Dean Malvick:Yeah. Most of our diseases of concern so remember that we could put diseases in 2 categories. The fuller diseases where the spores can spread around and the soil borne diseases that are coming from the soil within a field where the crop is planted. And for those within a field where the crop is is planted, that's where they'd have the biggest effect very likely. And, you know, there's there's certainly more studies are needed of this, and there's some work going on here right in Minnesota.
Dean Malvick:More come on that, I think, the results. But, nonetheless, two results that I can let you know about that have been published, I think both from Iowa. There's a study with corn suggesting that cover crops can increase seedling diseases, and the pathogens that cause them can. That doesn't mean they will, but they can. Whereas in soybean, they've seen no effect on disease for soil borne diseases, at least in a low disease situation.
Dean Malvick:So I I think there's a lot of variability in that, and it probably would not be a consistent management tool everywhere, but some places, it might be a benefit. And based on what we know now, the risk the negative risk is probably a little higher in court, although we we have more to learn on that as well.
Claire LaCanne:And when we think of green bridges with with diseases or with insects, maybe we think of a little more risk if they're similar, right, similar plants or, same kind of family. So if you did like a rye before corn, that might be setting you up possibly, right, for a little bit more, risk than if you're switching your your groups are kinda rotating.
Dean Malvick:Yeah. Yeah. I guess a little bit more about that is many of these pathogens, again, that some of them have a wide host range, meaning they can infect many different kinds of plants. And if we bring up Rhizoctonia, for example, that's that's a wide host range pathogen. That can affect a lot of things.
Jeff Coulter:Mhmm.
Dean Malvick:And, whereas Phytophthora has a much lower host range. Only soybeans, as far as we know. The Phytophthora is sojae are common pathogen on soybean. But also that pathogen can survive for a very long time in the soil in the absence of any host. So we're not aware of anything that's really clear that we can do to the soil microbially that will substantially fungus that causes that, again, a wide host range, seems that fungus that causes that, again, a white host range seems to live in the soil for a long time and can probably live on on many different kinds of plant roots even if it doesn't damage them severely.
Claire LaCanne:Good. Yeah. Thanks. That's good to know. Yeah.
Claire LaCanne:I I guess I would just ask you, Dean, if you're after any particular samples, if anyone sees anything in their field, and if you could talk about the resources that people can use that we have here in extension, to help diagnose diseases or, you know, figure out what's what's wrong or going on in their fields if they have issues pop up this year?
Dean Malvick:Yes. For diagnosis, we have the digital crop doc, which is a an online service provided to the University of Minnesota Extension. And sample well, photo photographic samples and descriptions of problems can be submitted through that, and that would be submitted to experts. And, in many cases, we can provide a diagnosis that way. And if that isn't adequate, if we can't provide a diagnosis based on pictures and descriptions, you know, we'd suggest samples be sent to the Planty's Clinic here on the Saint Paul campus at the University of Minnesota, where they are equipped to address, diagnosis of many, many different kinds of samples.
Dean Malvick:And as far as resources, you know, there are a couple we're putting in the materials. Again, there's that corn IPM pipe map that will describe and show the known location of tar spot. So you can kinda see how it's spreading and developing across the country. And I also put a link in there for the Crop Protection Network, which has a a a wide range of resources on all these diseases that I mentioned and many, many more. And the other question, Claire, that you brought up, are there samples that we would like to receive if people see something of interest?
Dean Malvick:And, yes, I would say a few. Phytophthora, we would like. Anybody suspects Phytophthora? We have a research project going on here with funding from Minnesota Soybeans that we'd like to understand that disease better. And that's with, doctor Megan Katie and primarily in her lab.
Dean Malvick:And then we'd also like samples of sudden death syndrome, if you suspect any, in the northern half of the state. You know, we well documented this disease. Many of you have seen it, you know, in many places in southern Minnesota, but we've not seen it in the northwest part of the state very much, if at all. And so we'd like samples from there, you know, anywhere north of I 94, basically. And what else?
Dean Malvick:Froggattley Spot. We'd like to confirm again where that's developing and what kind of resistance it has to fungicides. So those are 3 types of z samples we'd like, and and I should mention tar spot too. You You know, you can look at that map again and see where you've seen Tarspot and found it in the past in Minnesota. We'd like to know where it is anywhere outside of those areas, which is, you know, outside roughly the lower third of Minnesota primarily.
Claire LaCanne:Sounds good. Thank you. I a question just came up and we're at the end of our time here, but I do think it's, a good question to just address here quickly. And it's a, will conditions this year create higher pathogen populations for next season?
Dean Malvick:In some cases, yes. Some cases, no. I think a lot of these pathogens are are are so prevalent that that all we need are the right weather conditions and a susceptible crop. But in some cases, yes, it will. We'll we'll have more pathogen in those fields and the risk will be higher.
Claire LaCanne:Alright. Yep. Thank you, Dean. And we'll wrap up here. We'll say goodbye to everyone.
Claire LaCanne:Thank you for attending this week's session of Field Notes. And again, I want to thank our sponsors, the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council for making these sessions possible.
