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Join the University of Minnesota Extension Crops team in addressing all your crop-related questions this growing season, from soil fertility, agronomics, pest management and more. We will tackle issues as they arise to help you make better crop management decisions this season.
Alright. Well, welcome, everybody. This is gonna be another session of strategic strategic farming, Field Notes. This is our summer edition. So weekly throughout the growing season, we try to, have this on Wednesdays for a half hour in the morning just to kind of address any, current topics, things we're seeing in the field, etcetera.
Ryan Miller:And so, we wanna thank our sponsors for this program, both the Minnesota Corn Research and Promotion Council as well as the Minnesota Soybean Research and Promotion Council. And, this week, we decided to kinda, talk a little bit, or focus a little bit more on corn, I guess. And so we've got a couple of, panelists today to address some corn related, topics as we, get in the season part of the season where, corn has, tasseled or is in the process of stirring the tassel, and we enter those reproductive stages of corn. So, we've got two panelists today to to help address questions. We also have some, notes here from Dean Malvik, who unfortunately wasn't able to join us today.
Ryan Miller:But Dean, our plant pathologist, has, got some comments related to fungicide applications and some, foliar diseases, both on corn as well as he's got a couple of comments on, on on soybeans. But, anyways, we'll get to that with our live panelists here today, though. We've got, Jeff Coulter, our corn agronomist, with the University of Minnesota and and extension, And we also have Brad Carlson as we know. He's a very much a, he's a crops educator, but he's, he's very focused in on the nitrogen topic. And so I've, brought him on board just to kind of, address some of those late season nitrogen and corn topics, and, and so we'll go with that.
Ryan Miller:And, please, feel free as, things pop up. And if you wanna ask questions, you can type a question into the q and a at the bottom of your Zoom screen there. And if we're sharing any links, we'll share those through the chat. If you have any technical difficulties, please also access us through the chat function. And, again, this is meant to be driven by you.
Ryan Miller:So if you're out there listening, feel free to ask some questions, and, and we'll try to help guide the the discussion in the direction you wanna see it go. So with that, we're gonna welcome Jeff, and he's gonna maybe make some comments, Jeff, on on what you're seeing with the corn crop. And, you know, we've got some pretty hot weather the past handful of days and looking out in the next few. I mean, we're kinda in that what they're calling a heat dome. And so, curious to get your thoughts on on what's in store for the Minnesota corn crop.
Jeff Coulter:Yeah. Thanks, Ryan. Well, you know, it seems like the crop is definitely ahead of normal. It seems like, tasseling occurred about a week earlier than what it usually does. You know, we have pretty good moisture conditions a lot around around much of the state.
Jeff Coulter:However, you know, we're starting to dry out a little bit now. There's not a lot of rain in the forecast. You know, looking at the seven day forecast, not much. Basically, no chance of rain in a lot of places. So I think we'll see, you know, over the next week or so, it's gonna get progressively drier.
Jeff Coulter:Fortunately, it looks like, you know, about Tuesday next week, the temperatures are gonna dip again. So that'll definitely be nice for the corn, giving it a little relief from this this heat. You know? So I guess the question that I've been getting a little bit is, you know, what's the effect of this heat on the corn? Well, you know, fortunately, the heat that we've seen in much of the corn growing area around Minnesota hasn't been quite as hot as it's been around the Twin Cities.
Jeff Coulter:You know, a lot of places experience, like, the low nineties. And if you have sufficient soil moisture, low nineties is not a bad deal. Corn can do do fine at that. Once we start to get above that temperature, then the stress starts to kick in a little bit, especially if we're under drier conditions. And if you're experiencing drier soil conditions, and there are some parts of the state that has that, you know, parts of the Southwest Minnesota for sure, and then other other areas of the state, you know, basically, dry conditions at this time of year once soon after tasseling generally causes, the the tassel, to develop quicker and the silking to kinda slow down a little bit.
Jeff Coulter:So under, dry hot conditions, that can result in, pollen being shed before all of the silks have emerged, and so some some of the last silks to emerge may not get get some of the pollen as it has dropped earlier. Another question that I get is, what is the effect of the high temperatures on pollen viability? Well, once, temperatures get into, like, the mid nineties, then pollen viability starts to become become an issue. And once we get temperatures in the hundreds, pollen is basically gonna, be dead. That's that would be available, that that's being dropped.
Jeff Coulter:But, fortunately, pollen shed occurs in the mornings, for the most part, and we never get those kind of temperatures in the mornings. So the pollen viability issue, generally isn't much concern in Minnesota even in this year. I think, you know, things are looking pretty good overall. I think this heat is not a great thing to have, but it's better that we're having it this week rather than next week. I think next week's gonna be the big week for for corn yield.
Jeff Coulter:You know, during that, we're gonna have a lot of pollination occurring throughout the state next week. And for the corn that pollinated earlier or is pollinating right now, next week's gonna be very key for, retaining those kernels that have been pollinated. So, stress next week would, favor the kernel abortion on some of the the corn that was early to tassel and would and and could hinder the pollination for the corn that will be tasseling next week. But, fortunately, it looks like the temperatures are supposed to drop, so that should really help the corn. And if we could pick up some moisture next week, that would be a a great thing as well.
Jeff Coulter:So, that's kind of an update on the on the corn crop and, silking and all that. I'll turn it back to Ryan.
Ryan Miller:Alright. Excellent. So, just seeing if we have any, q and a coming in here. It looks like alright. So from an anonymous attendee, when will we know if we got Nick?
Jeff Coulter:Yeah. So if you walk out in your field and you see that, you have very long silks, that means that they didn't receive pollen and they keep growing. The silks will grow about one inch per day until they're pollinated. So you go out there and you see very long silks, that means that those long silks didn't receive pollen. If they're more normal size, then, pollen probably occurred.
Jeff Coulter:And you can also, you know, walk out in the field and, you know, pull the ear the the husk back, that kind of thing, and, and see. But, basically, if you pull unwrap the husk very carefully and you shake it and the ear and the silks fall off, that means that they've already, received pollen, within the last one to two days. If they're still attached, they haven't received pollen or it's been very recent. So kind of the the the test is to unhusk an ear very carefully, shake it, see how many, silks are attached, and those that are attached, haven't received pollen or they just received it within the last day.
Ryan Miller:So, Jeff, what what kind of timing do you recommend for for doing that analysis, or or tests, I guess? Do you do you wait a week after silking, or what what's your you know?
Jeff Coulter:Yeah. It's best to wait a few days because there's not much that you can do about it anyways. If you're doing it right away after pollen shed, you know, you may still have some silks attached that just recently received pollen. So, you know, probably wait a few days after the, the bulk of the pollen has dropped.
Ryan Miller:And so when pollen hits a silk, how long does it take for that to fertilize the the plant?
Jeff Coulter:Within about twenty four hours. So the pollen a single pollen grain lands on a silk. It germinates, and then it starts growing, down the silk and to reach the the ovule or the potential kernel, and it it will hit that within about a day.
Ryan Miller:A day. Okay. So that's good to know. So we got another question here, Jeff. Seems, there's a shift happening to silking earlier before tasseling.
Ryan Miller:Any benefit of that or impacts of smaller tassel size? And I'd I'd kinda concur with this this statement question here. You know, it used to be in my mind we had the tassel and silking, and now it kinda seems to be synchronous with one another at least. And the this individual is indicating that perhaps even seeing silking ahead of, tasseling, I guess, as I read, this question. So just kinda curious to get any comments, related to the whole timing of silking and and tasseling.
Jeff Coulter:Yeah. I've noticed those same things as well, and, I believe that's a benefit for us to have, silking and tasseling occurring at the same time, especially in a year like this when we've started to have these, warmer temperatures, right around the start of silking in some cases. So I think anything we can do to tighten up that window is great. And, you know, if the silks are coming out a day before the pollen shed, you know, I don't think that's a big deal either. They'll continue to grow until they get pollen.
Jeff Coulter:So anything we can do to kinda tighten that up, like you mentioned, I think is in our favor.
Ryan Miller:Yeah. That's good to know. So how long does a tassel then, poll drop pollen? I mean, how how how long is that gonna occur, I guess?
Jeff Coulter:Yeah. Probably over, you know, several days. It's gonna depend on the temperature. You know, hot, windy conditions is probably gonna drop more of its pollen earlier rather than spreading it out. You know, cooler, moister conditions, it may spread it out over over several days, but, you know, I would say the bulk of it's gonna be done in about five days.
Ryan Miller:Okay. So just a frame of reference, I mean, folks, we did have seem like kind of a a wider tassel window here as, as I drove across actually part of Southern Minnesota, today. It seemed like some fields were fully tasseled, and others were in the process of tasseling. And so that's a good frame of reference, I think, for folks that, are trying to evaluate the the success in pollination and kinda when when that might have occurred with the with their, corn crop. And so once we get pollination, Jeff, like, how long do we have to be concerned with stress?
Ryan Miller:I mean, you know, where where is kind of that critical period when when things are more determined? I realize if we turn the moisture off and turn the heat up for the rest of the year, that's not gonna be a good good situation. But I know there's more of a critical window around the time of pollination as far as heat and moisture. And when do we kinda get out of that real critical zone?
Jeff Coulter:Yeah. So, basically, the first two weeks after, silking is pretty important for retaining kernels. Any stress during that period, any kernels that were set, they can be lost. They can dry up, wither away. And then looking a little more broadly, you know, the four weeks after silking is pretty important.
Jeff Coulter:So all of August is important, but especially that, you know, the first two weeks after silking. If I had to give it a rating, I would say that week of pollination, the the index would be a 10 out of 10, which is that's, like, the most important period. Then, you know, the two weeks after silking, rate that probably a nine, And then the the weeks three and four after silking, rate that as an eight. And then as we get closer to, harvest, that index would go down slightly. But, you know, basically, most of August is is still gonna be important for remaining for retaining kernels.
Jeff Coulter:But, you know, the next two weeks are super important, and then the remaining two weeks after that are also quite important.
Ryan Miller:So you rank 10 out of 10 the weeks leading up to tassel. Is that what you said?
Jeff Coulter:No. That would be the week of, pollination. The week of pollination. Yeah. So, basically, once we get to, once we start to get to that dose stage, you know, we're out of the, the colonel abortion window.
Jeff Coulter:The blister period on the colonel is is at high risk of colonel loss. As we get to the milk stage two, we can lose kernels, but it's you know, the risk starts to go down a little bit. So
Ryan Miller:Okay. So let's talk a little bit about moisture. There's a question that came in, and their comment here was a a common question. Is July makes bigger corn yields. Right?
Ryan Miller:August for beans. And so let's maybe, talk a little bit about moisture and moisture demand as as we get later into into August and maybe what we need to, to see to ensure we have enough moisture moving through
Jeff Coulter:the season. Yeah. So that's that's definitely right. You know, July for corn, August for soybeans, and that tends to relate to the critical periods for those crops. And, right now, corn is using probably a third of an inch of water per day.
Jeff Coulter:So it's probably gonna maintain that for a while, and then it'll go down a little bit. Fortunately, we had a drier, first half of the year, so I think that we probably have a pretty deep root system, and that's accessing, some of that deep subsoil moisture. Hopefully, you know, that's the case, and, hopefully, we get pick up some moisture later next week, that would be really great. But if we don't, I I think we're gonna be seeing more stress, and we're gonna be seeing, more kernel abortion.
Ryan Miller:In this time frame, now for the next few weeks, you're thinking?
Jeff Coulter:Mhmm. Yeah. So I think I've heard from a lot of people, they think the crop looks pretty good right now, but, you know, there are some signs of moisture stress. And, you know, as we continue these warm days with, no moisture, you know, eventually, we're gonna run out unless we get some rainfall. So, you know, I think we're in pretty good shape, but I think these temperatures this week are definitely taking the top off of the yield.
Ryan Miller:Okay. So a question here about how, the ear fills, and the question is about does it fill from the bottom first and the tip last, or how does all that work?
Jeff Coulter:My understanding is is the middle part of the ear, those kernels are kind of the the ones to get a set first and then towards the base of the ear, and then the last is the, the tip of the ear. So when we have, you know, drought stress, during pollination or after pollination, it's generally the kernels at the tip that are are lost first because they're fertilized last. And those silks and, developing kernels are very high in moisture content, so they're they're really demanding a lot of water from the plant. And anything that's any stress that's inhibiting that is gonna affect those.
Ryan Miller:Alright. Well, that's good. Well, here's a question. I'm actually gonna take this one on. So we are seeing tons of waterhemp in our areas.
Ryan Miller:Everyone else, any ideas? And I think, I think, yeah, that's a that's a common observation. Particularly yesterday, I was surprised at how much, waterhemp we're seeing already over top the soybean crop. And, actually, the last week or so, I've been doing a fair amount of scouting for corn leaf diseases, and, and there's a there's a reasonable amount of, misses, I think, in our in our corn crop even with, with some of the waterhemp out there. And so that continues to be a challenging weed.
Ryan Miller:You know, we're really focused on trying to manage this, you know, in the soil. So, like, keep kill them in the soil or however you wanna consider it, but using the pre emerges to provide emergence of the waterhemp because once it's out, it becomes difficult to control. And, you know, if it, if it escapes your pre emerge, if it's not gonna meet you know, if you've already put a post on, it's it's gonna be, it's clearly not gonna have control. And then on the other side, a lot of waterhemp is showing some issues with, different post emergence herbicides not working. So they we've got a lot of multiple herbicide resistant populations of of waterhemp, and so it's gonna continue to be, one of the most problematic issues for us as far as pest management in both corn and soybeans, because of its timing of emergence.
Ryan Miller:And the other thing that we know about waterhemp is it does like heat, humidity, moisture, and so we've had some recent rainfalls if we look back to the beginning of the month, and now we've got some really hot temperatures. And so we're seeing a lot of waterhemp start to flush, and and that's just it's MO. I mean, that's how it works. And so so where we don't have canopy in our soybean crop, and, if we put a pre on at planting and maybe we didn't use a residual at post application, some of that is running out of steam. And so we've got an open canopy in soybeans, and there's opportunity given the moisture and heat conditions for more waterhemp to flush.
Ryan Miller:And if we've already put our postemergence herbicides on, we may need to consider another application before we, we see some of those application windows close based on some of the cutoff restrictions for postemergence herbicides. So something to consider here before, too long. If you're seeing those, you know, you might wanna get out and consider how you're gonna manage those or think about the future of what you might do different. So, again, got that one answered. And let's see here.
Ryan Miller:Brad, I think we we should probably bring you in a little bit and talk about where the corn crop is at, where is the nitrogen uptake at. And I know some folks talk about these late applications of nitrogen fertilizers, you know, in these kind of stages where we enter the reproductive phases, and and I just kinda we'd like to get your take on that. And, as you're moving through that, I know some of our area in Southeast has had some excessive rainfall. We've had saturated soil conditions. And so, you know, immediately, start thinking about denitrification and losses of nitrogen to the atmosphere just because, of those, conditions where the soil has been saturated.
Ryan Miller:And, you know, is that a cause for concern for folks in those areas where we've had, you know, if you look at Marrow and Fillmore Counties, they've had, you know, areas that have had over 10 inches of rain. Across that whole area, though, I think most of them are well north of five inches of rain, so very, very wet conditions.
Brad Carlson:You you know, in general, Ryan, our higher organic matter soils are just fine. There's probably no reason to be thinking about putting on any supplemental nitrogen almost regardless of what the crop looks like. You know, we do have have really for a very long time recommended multiple splits of nitrogen in irrigated situations. And so, you know, from that standpoint, a lot of the irrigators are probably planning on still putting on a little more nitrogen. If you look at the overall uptake of nitrogen in the corn crop, you know, really the critical point is where we're in that rapid growth phase through June.
Brad Carlson:Certainly, there's still a significant amount of nitrogen still yet to be taken up by the plant. But, you know, if we set if we cause an imbalance in the field, you know, in June and starts getting ragged and and, you know, changing growth stages in different places and and uneven heights, you know, we really can have some problems. We really didn't see that. It really, to my observation, I haven't really seen it anywhere in Minnesota. I I I will admit I have not just because of my travel patterns, I've not traveled through the central and and western Northwestern part of the state here during, you know, the last month and a half or so.
Brad Carlson:So may maybe there are a few spots, and we all know that there's always going to be some isolated areas that experience some some climate extremes. I was mentioning before we went on the the air here that we had a rainfall event where we got about three and a half inches of rain. At my house, the Southern Research and Outreach Center, which is 13 miles away, got 1.1. You know? And so there's always gonna be those spots that get those, you know, the the the super precept areas where you're gonna have kind of some micro problems that are represented across the landscape.
Brad Carlson:So that being said, you know, all the rainfall we got that kind of shut off in the last week or so, you know, was coming pretty regularly. We know we came into the season this year relatively dry, and so really kind of the good news there is in for the most part, we expect that the crop roots, the corn roots are gonna be fairly deep. That will serve us well here in the next couple weeks if we're not getting a lot of precip, but should be able to get a lot of moisture from further down. We are in perfect condition to really kick things into overdrive for mineralization of nitrogen where there's ample moisture and with the heat, we expect there to be a lot of nitrogen release. If your soils are at least two and a half percent organic matter and higher, pretty significant amounts of nitrogen are gonna get released now in the the the coming weeks.
Brad Carlson:If it does dry out towards the surface, of course, that can shut some things off. The thing, you know, we like to remind people of, though, is, you know, occasionally, you'll hear these suggestions about late season nitrogen post hassling nitrogen. A lot of that comes from the South where there is not you know, in most cases, you're dealing with soils that are one and a half percent organic matter and lower, and we're not talking sandy soils. We're just talking about old soils like in Missouri, you know, and and the Mississippi Delta and places like that. So I guess for from our standpoint, we usually see enough nitrogens coming out of the organic matter to satisfy the needs of the crop.
Brad Carlson:Really, your applied fertilizer, we really needed that to get us through the rapid growth phase of the crop. And from here on out, we we, you know, we should be able to get by with whatever of that is left and then whatever is being supplied by nature. So going back again to some of that rainfall a couple weeks ago, coming into the year dry, of course, it took quite a while actually to completely recharge the the cell profile. And then as you look at the drought monitor, you'll see that the southwestern corner of the state still is listed as abnormally dry. I'm pulling it back up here.
Brad Carlson:I mean, there's a there's a big bull's eye in the North Central part of the state where we don't grow a lot of corn. So from that standpoint, if Itasca and and Kuchin County are dry, we're probably not gonna you just not gonna register a lot from sorry if that's where you're at. But but even the Northwestern side of the state, I mean, it's not looking particularly dry when you look at, like, say, Kitson County and and on the northern edge of that either. So, you know, we we probably saw some of our lower areas, like in my area where we got a lot of rainfall, we did see, you know, some ponding and the areas that we drown out usually every year ended up drowning out again because that's kinda where we're at. You know?
Brad Carlson:But the we're we're we've got so much drainage installed now that we really have minimized those areas. It's just areas that are low in the landscape, and, you know, probably a lot of the guys that have those spots just understand this is just the way it is when you've got that in your field. I am not seeing yellow corn anywhere other than in those areas. And so as far as late season stuff goes, you know, we we we don't have a recommendation for that. The one piece of research that I think was most instructive on this was back a couple years ago where we did have some significant moisture and nitrogen stress earlier in the growing season.
Brad Carlson:While it was not set up this way, it's hard to do a study on rescue treatments because it requires that you have excessive rainfall and how do you predict that, you know, when you're designing your experiments over the winter. But the condition is set up to be right for that. So Jeff Vetch at Waseca ended up putting on some rescue treatments late in the season. Or I shouldn't say late in the season, but later than normally, we would have applied nitrogen. And while he did get response to that rescue treatment nitrogen, didn't get a response above 20 pounds.
Brad Carlson:You know? And so, you know, what that kinda tells us is, you know, even if the crop is lacking, the amount that we're able to pull back with by by putting on later season nitrogen even, you know, again, when we see visual demands of that really is quite limited. So I've been kinda rambling, but, you know, that's kinda that's kinda where we're at. And I guess, you know, as an overall kinda just wrap it up, overall recommendation is we really don't recommend putting out any further nitrogen other than the core structure soils that probably plan to do that already.
Ryan Miller:Excellent. So, thank you, Brad. We'll move, kinda change gears here quick. We got another question about new pre use or chemicals to help us with pigweed control. I do know that, Difufenikin received a registration from the EPA most recently, and we've had a chance to look at that product, under the trade name Conventro in both corn and soybeans.
Ryan Miller:We've had, some opportunities to see that, and it it it does offer some promise as far as pigweed control. That said, it is very narrow in spectrum. It's a pre emerge, soil applied product that that does, control pigweed species, but is limited to the pigweed species. So when we're using that product, we're gonna need to look at rounding out our our, weed control. You know, if we wanna pick up some grasses, things like giant ragweed, we're gonna need to to look at adding some different chemistries, into the mix.
Ryan Miller:But it is a new thing that's coming out and, still yet to receive state registration, so we'll have to wait and see, what happens with that this coming, season. So with that, do wanna make mention here, Dean Melvik gave us some notes, so we'll quick hit some of these high points here. Tar spot, in the state, is at low levels. They have low level detection, so not severe, incidents, or severity. In Southwest Minnesota, there have been a couple of fines.
Ryan Miller:There have been a couple reported or one, I think, in Southeast Minnesota. And so we're kinda at that point, we're starting to maybe find it. But, again, it tends to be a disease that comes on later in the season. And so, so I think we just need to keep scouting for that one as, as it you know, we have to get into conditions where we see the disease, and then we see some favorable conditions for disease development, which tends to be later in the reproductive cycle of corn, when temperatures are cooler and we have some more moist conditions. Certainly heading into these hot, dry conditions here for the next, week or maybe even two, I'm gonna hold back on, personally on on spraying for tar spot if that's a major concern for me.
Ryan Miller:Again, out there scouting though to look for the evidence of that disease. Northern corn leaf brite, that was an issue for us last year, tends to be more of an issue in cool moist conditions. So, again, it's been at real low levels in Minnesota and probably not too much of a concern, but, again, one to scout for because it can raise, some issues, particularly, in my experience in corn on corn situation. So something still to be tuned into, but our environmental conditions and the disease incidence and severity seem pretty low with that right now, so, not making me real excited. Southern rust is another one that really bit us hard last year.
Ryan Miller:You know, we had some fungicide trials out, and we saw a 20% yield reduction where we didn't have a fungicide on, and we had significant Southern rust followed by some tar spot. That said, you know, it's been in real low incidence. So this is not an endemic disease to Minnesota. The spores have to come in every season, and so, we have to look to our states to the South where it overwinters, and they have not had terrible situations. There's been some reports in Texas.
Ryan Miller:The reports out of Florida, Georgia have been, nonexistent. And so, it's been much lower of a problem for them in the South, and so then that typically typically means this can be less of a problem for us in the North. This time last year, we were finding southern rust, on the outside edges of the cornfields pretty easily in the lower canopy. And as the season progressed here into late July and August, we started to see that disease move into a lot of fields, through the mid canopy and certainly saw a benefit from spraying fungicides. But this year is kind of, looks like it's likely not to be an issue, but, again, one to continue scouting for as as you're out there going forward.
Ryan Miller:So we'll have more of this. I'm gonna type up some of these details, and it'll come out in the crop news with that. With that, though, I wanna do thank our sponsors and our panelists again. Thanks, Brad and Jeff, as well as thanking our our sponsors, the Minnesota Corn Research Promotion Council, as well as the Minnesota Soybean Research Promotion Council, for promoting and helping support this program. Next week, we will have Faye Yang on, our entomologist, corn entomologist, and he's gonna be talking about corn rootworm and other pests that kinda starts to become an issue this time of year.
Ryan Miller:And we can do some monitoring for that pest to change management, in future years. So so certainly come on back next week, and we'll talk about corn rootworm. And, with that, I wanna say thanks for tuning in, and, we'll see you next week.