Corn agronomy updates and preparing for soybean insects

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Anthony Hanson: Alright welcome back to strategic farming. You'll notice everyone and good morning.
Anthony Hanson: So these sessions are brought to you by first University of Minnesota Extension, along with generous support from Minnesota farm families through the Minnesota Soybean Research Promotion Council and the Minnesota Corn Research Promotion council.

Anthony Hanson: So we're glad you could join us today. Today, we're going to talk about corn agronomy, especially pollination. And what's going on there and then. Also, what's happening with soybean insects. So first, we're going to welcome Dr. Jeff Colter, our tech extension corn specialists with University of Minnesota Extension.

Anthony Hanson: And we are gonna work with Dr. Coulter first Ts, leave a little bit earlier. So someone does have a question related to corner grown me. Please get those in earlier before Jeff has leave out halfway through the session here.

Anthony Hanson: and with that

Anthony Hanson: I think I'll turn it over to Jeff for kind of what's happening with the status of corn across the State. I know we are getting a little bit of rain this morning in Southern Minnesota, or just about to. It. Looks like But draw conditions haven't happened across the State. So how is that been affecting what we're seeing in terms of crop quality so far?

Jeff Coulter: Thanks, Anthony. Well, you know, we're about 8 to 10 days ahead of normal normal, depending on where we're at across the State. And on top of that we were planned about 2 weeks later than normal. So the corn has really growing quickly with the warm temperatures that we had earlier this summer generally warmer temperatures than average during the vegetative period.

Jeff Coulter: Up to now, that doesn't really hurt the corn too much. But when we have warmer temperatures during pollination and during rainfall that can have more of a detrimental effect on the crop. you know right now.

Jeff Coulter: you know, it's pretty dry in a lot of places. It's not an extreme drought, except for in a few isolated areas. But it's it's quite dry.

Jeff Coulter: Some rainfall was picked up recently. It looks like there's a little bit of a chance later this week. But I think that's questionable

Jeff Coulter: The good news is that the temperatures look like they.

Jeff Coulter: you know, they've really subsided, and are going to be more mild here over the next week, and that's going to be very helpful for the crop. you know, if we can keep those temperatures in the eighties for the highs

Jeff Coulter: that's going to minimize stress on the corn.

Jeff Coulter: I was seeing some tassels as early as June 30. In some places on irrigated sands. And then, right now a lot of places are starting to tassel or are getting very close. It looks like next week is really going to be the heart of the pollination period for

Jeff Coulter: much of the corn in Minnesota, and fortunately the temperatures look like they're going to be favorable for the crop, so that the crops not going to be using an excess amount of water. But we are definitely in the critical period right now for yield determination and corn, and that's going to last through

Jeff Coulter: early August. So if we can have soil moisture levels be sufficient that we're not stressing the corn that is going to

Jeff Coulter: help to maximize, yield, and any soil moisture, stress that we're experiencing between now and then is going to have some sort of a degree of

Jeff Coulter: reducing your potential in the crop.

Jeff Coulter: Now, there's basically 2 ways that you can be reduced in corn due to drought stress at this time of year the first one is it. It causes a delay in silking, but it really doesn't slow down the tasksly emergence or pollen shed.

Jeff Coulter: and in this case, some of the silk setting merged late from the tip of the year do not receive pollen

Jeff Coulter: and Therefore those potential kernels never are fertilized, and they don't develop into actual kernels.

Jeff Coulter: that's not quite as common in Minnesota. The thing that's more common in Minnesota is that we have a successful pollination where all or the majority of the potential kernels receive pollen and they develop into actual kernels. But then it gets try. And those

Jeff Coulter: kernels that were fertilized, especially near the tip of the year, they turned into kernels. But it's dry, and they have a high demand for moisture, and then they just kind of dry up and triple and are lost. So that's

Jeff Coulter: typically the most common way that we reduce yield in Minnesota due to drought stress at this time of the year.

Jeff Coulter: The other thing to remember is that once we get past this critical period, we get into mid August and beyond. Then we're starting to move into the grain filling period. And even though that's not as critical as the pollination period window right around. Now. that does have a a great potential for reducing yield, because that's determining the size of the kernels. So there's basically 2 yield components in corn. The first one is, how many kernels can you establish?

Jeff Coulter: The second one is, what is the size of those kernels? So right now, we're in this period where we're going to be establishing, how many kernels do we have.

Jeff Coulter: and whatever we can? Well, whatever happens that allows us to have more kernels is going to help us to have higher yield. So it seems like right now we're under some degree of stress in the corn.

Jeff Coulter: I'm not too concerned about it. The upcoming temperatures look more favorable.

Jeff Coulter: But we're definitely the corn is definitely under stress. In most areas.

Jeff Coulter: it's probably going to take the top off of yield potential.

Anthony Hanson: And Jeff, we actually did have a question come into. They're just wondering what exact plan stage is determining the number of kernels that are established. So it is pretty much right around tasling through pollination. kind of what window or folks kind of want to keep an eye out for that in terms of when they can be

Anthony Hanson: no confident that the number of rows or 7

Jeff Coulter: yeah. So in corn, the number of rows per year the girth of the kernel. That's just that's determined around the B 7 stage. And then the number of potential kernels or the potential length of the year is determined between about v. 8 and

Jeff Coulter: up until just before tasseling, and then during the pollination period, where the tassels first come out up until

Jeff Coulter: through the blister stage.

Jeff Coulter: which is a Co. About 12 days after the tassels first emerged. That's when we have potential for

Jeff Coulter: a good potential for the N for the

Jeff Coulter: kernels at the tips of the year to be lost.

Jeff Coulter: either due to drying out or not receiving pollen during the pollination period, and it even goes in in through the milk stage as well, so we can lose kernels up through the milk stage, and then, after the corn reach corn, gets through the milk stage and moves into the dent or

Jeff Coulter: the DOE stage. At that point we can't lose any more kernels, and at that point. Any stress at that point and beyond is just going to reduce kernel size.

Anthony Hanson: Thanks. So in terms of variability across state, we talked a little bit where you know, folks especially further south are starting to see more tasseling going on up here kind of central West Central Minnesota. There are a lot of fields that you know you. If you look in the world and kind of dig in there, you'll see the tassel. But yeah, maybe you got a week or so like you said

Anthony Hanson: so. Are we expecting any? You know? Differences in the corn crop across the State just based on know that difference in development in terms of how whether it might affect things, or is it looking pretty consistent in terms of you know this cooler weather benefiting across the board.

Jeff Coulter: I think across the board, this cooler weather is definitely going to help us. It's going to reduce the amount of water use by the crop

Jeff Coulter: quite a bit. so that's that's gonna help us kind of skate through this, probably without having as large of yield reductions as what we would if

Jeff Coulter: it was, say in the low nineties.

Jeff Coulter: so That's favorable. But there is a lot of variability out there, you know. Some of that corn was planted quite early and tasseled early and looks good, others others was planted a little later, and is a little behind, but not too far behind, and then we have areas that were planted earlier had emergence problems. And there's just a lot of variability in those fields due to that. But yeah, it's I think we're on track for kind of an average year for an average crop.

Anthony Hanson: Good. so this is another question I had come in, and it's something we usually don't think about this time of year too much. But

Anthony Hanson: how cool is too cold for corn in terms of pollination time. When would we have issues? because some folks are kind of wondering like, well, it's cooling down, is it? Too cold? But I think we're not worried about that right now. But When would it actually be too cold for corn this time? Here? Yeah, I'd say, when the high temperatures get you know, below the low seventies. Then we have some.

Jeff Coulter: you know.

Jeff Coulter: potential for some issues to develop. Sometimes calling occurs if there's cloudy conditions potentially

Jeff Coulter: with cooler temperatures. But generally I I'm not too concerned about the cooler temperatures the highest point in the world. The current areas that are basically or California that are irrigated that have high temperatures during the day with lots of sun, and then at night it cools down. So I think.

Jeff Coulter: I think we're on track.

Jeff Coulter: with this cooler temperatures to, you know. Reduce water, use and help us out quite a bit. There. I wouldn't get too concerned until the low temps get into the or the high temps get into the low seventies or or below.

Anthony Hanson: So I know. you know some folks I'm getting hail on some parts of the State. So, given the stages, we're at. What if folks wanted to keep N out for what's maybe not so much concern at these stages in terms of heal damage.

Jeff Coulter: Well, right now is the worst time of the year to receive hail, damage, and corn essentially, because we've got almost all or all of the leaves are exposed, and we haven't set any kernels or filled any grain at this point. So if we're losing leaf area

Jeff Coulter: there's there's really no more leaf area in the plant that's going to come out to replace that

Jeff Coulter: things to think about this time of year with hail. Damage is You know. How. How's the plant doing Did we lose the tassels? How are the years doing? You know we can lose quite a few tassels, and still have plenty of pollen out there to spread around and and fertilize all the silks. Assuming that the remaining tassels are fairly evenly distributed.

Jeff Coulter: You know, there, there can be 2 to 20 million pollen grains per tassel, and there's only about 800 silks per plant. So there's a way more pollen than there is silks, and if we got a little wind that that should spread it around

Jeff Coulter: the other thing to think about is, how is that that year was that damaged? And if the primary ear, the upper one, was damaged

Jeff Coulter: and hurt greatly, and then the the ear below it oftentimes will develop into the the full ear. So those are some things to think about. Also stock damage. look at some of the stock wounding. that can be quite severe. that could cause stock lodging later in the season.

Jeff Coulter: basically. Now is not a good time to get hail damage in your crop.

Anthony Hanson: All right. I know you got to run after this one last question for you. Do you want to make any guesses in terms of how do you think you's going to turn out this fall, just based on what we've seen so far? is going to be a, you know, pretty decent year just based on conditions. So far, folks have gotten through dry conditions. Okay, or is going to be, you know, roughly, average. Do you think

Jeff Coulter: I would say we're on track for maybe 5% below average

Jeff Coulter: potentially up to average, depending on on what's going to happen here, so if we start, pick up it, picking up moisture, and the temperatures remain favorable, we could do very well, but if it can, if the second half of the growing season kind of mimics the first half, where we have very limited rainfall, even if the air temperatures are down

Jeff Coulter: and more cool, like they are this week. that's really gonna take a toll on our crops. So I think we'll 5% below average or potentially averages

Jeff Coulter: kind of what we could look at. But you know, it's still quite early to make any

Jeff Coulter: guesses that are going to be real accurate.

Anthony Hanson: All right. Well, thank you. And May. Dr. Jeff. Culture has to run here. So thank you again. And we will transition over to soiping insects. And what's happening in that realm of crops there. So Dr. Bob Cook, thank you for joining us again here, and

Anthony Hanson: just to start off. it seems like you've kind of. Got a fuller plate now, with different insects we're dealing with and sleeping. So do you want to tell everyone just what is everything on your radar for soybeans this growing season for insects that you're dealing with.

Robert L Koch: Yeah, it's turning into, certainly an interesting year for entomology in in Soybean and and other field crops, and I guess, like, can I see? I always used to say, if an entomologist says things are getting interesting, farmers should be concerned.

Robert L Koch: you know. So we know there are all the issues earlier on with army worms. you know. So now we're kinda

Robert L Koch: transitioning into a lot of these issues tied to the dry weather. You know, it's a lot about you and Jeff. We're discussing the drought conditions, dry weather throughout the State that has a big impact on insect populations as well. And it really helps some of these insect and mic pests. So we're getting more and more reports and concern about grasshoppers, and that's been kind of building over the last 2 or 3 years with, you know, consecutive dry years.

Robert L Koch: grasshoppers are the foliating insects a lot of times moving into the fields from surrounding habitats, and they can be quite, quite problematic. spider mites are another issue. I think a lot of people know that that they're mainly problems under drought conditions.

Robert L Koch: we've been seeing mites in a lot of fields for some time, but numbers had remained pretty low, but I just heard through Bruce Potter that there are some fields in.

Robert L Koch: I believe it was West, Central and Southwest Minnesota that are starting to show some symptoms of injury from the might. So I think it's something that people will certainly need to be

Robert L Koch: paying attention to.

Robert L Koch: So those are kind of the 2 key insects that are really favored by the drier conditions. Another insect that we want to be paying attention to is soibi and aids.

Robert L Koch: Soybean aphids typically do not like the real high temperatures. It slows down. Their reproduction decreases their survival.

Robert L Koch: But we're getting into a spell now, as you and Jeff, we're saying, we're temperatures are moderating a bit, you know. So that's going to make things more favorable for soy and a good population. Growth. So I think folks are gonna definitely want to be scouting their fields now, paying attention to aphids as well.

Robert L Koch: And for you know, I think those burly planted fields

Robert L Koch: in the early part of the year are going to be the most attractive.

Robert L Koch: and as we did into the later season, you know you might want to transition and start looking at some of the the later planted fields.

Robert L Koch: yeah, I guess I'll let you see what you think of that. And what questions you have?

Anthony Hanson: Yeah. So continuing to unscip. And if they're, you know, each year we'll have folks earlier on kind of thinking. Hey? Should I be treating for saving if it's in early July? maybe they have a scholar and just found a few and are maybe thinking, well.

Anthony Hanson: there's that 258 threshold, but they're deciding to spray earlier. So what's going on in those situations? in terms of economics, and how that threshold actually works.

Robert L Koch: Yeah, that's that's always a concern, right? You know, if you're out there scouting scout in your field, you see some aphids, I think a lot of times. There is that temptation to

Robert L Koch: to hit them with an insecticide, you know, especially if you're going through with a herbicide, or, you know, making some other pass through the field. you know. What that's going to do is you'll get rid of those few aphids that are there.

Robert L Koch: But what that's also doing is, it's exposing that if it population to that insecticide more which can increase the chances for further insecticide resistance development. And we we know we have an issue with that for the pyrethroids in Minnesota, in the surrounding States

Robert L Koch: it exposes other pests in those fields to those insecticides which can increase the risk for resistance development in them. And we we had some indications of that for spider mites, you know. And several years ago

Robert L Koch: a. And you know we're thinking about the economics of it. The research to date is still showing that the 250, if it per plant threshold, is still pretty conservative

Robert L Koch: threshold for protecting soybean yield. So if you know, if you only literally have, you know

Robert L Koch: few aids per plant, it's it's not going to affect the yield of those plants. You want to keep scouting those fields to monitor those populations if it populations can increase rapidly, you know. So that's why we recommend scouting, you know, ideally weekly. But you know, maybe every 10 days to keep tabs on that field, and if the populations reach those higher levels, then start to sign up.

Anthony Hanson: And in terms of that, the 250 threshold. That's actually not the point where damage is occurring yet. Right?

Robert L Koch: That's right, I think, of the 250, if it's per plant as as the trigger point where you want to start lining up that insecticide application to knock that population down before it reaches those higher damaging levels.

Robert L Koch: And one thing we've been seeing more and more

Robert L Koch: in the recent years is aphid populations increasing to maybe 100, if it's per plant, and then kind of plateauing there. You know where in the earlier years, a lot of times, it would just continue to increase your skyrocket reach very high levels. But not exactly sure if it's you know, this new parasitic wasp, or some of the other natural enemies adjusting to it more and

Robert L Koch: knocking those populations down after they reach a certain level. So not to say that if it's will not reach outbreak levels and cause problems in fields. you know, we, we need to scout to determine which fields have the problems and then make our spray decisions based on that.

Anthony Hanson: And Bruce Potter has a good comment, too, that when we're looking at those special, this, the average of all the plants in the field. Not just the worst plants. And yeah, you you might in a bad year find a plant that has a thousand 2,000 aphans, and that isn't always a signal that you need to be treating. It's still going to bump your average up a lot, but

Anthony Hanson: if it's just one plant and all the rest are relatively clean. Then, yeah, you really aren't in that situation, or you may need to treat.

Robert L Koch: Walk around that field. You know a lot of times you recommend like making like a M shape pattern kind of zigzagging through the field to make sure you get good coverage. And you're not making that decision just based on a hotspot.

Anthony Hanson: Yeah, that's good point.

Anthony Hanson: So, Bob. in terms of other pests I know Northwest Minnesota. They were dealing with Green. Go over worm up there, so that

Anthony Hanson: In that case, what was happening with that test and is that some folks should we keep an eye out for still, or is that something that's you know.

our early season?

Robert L Koch: Why so green clover worms their a green colored caterpillar, if you look really closely, they've got 3 pairs of a domino pro legs. They've been the main caterpillar that that I've seen in Minnesota soybean over recent years. We also get some fissile caterpillar but this year it's been mainly the green clover worm

Robert L Koch: talking with Angie Peltier up in the Northwest. Yes, they were seeing some pretty high numbers up there, I think, in some fields.

Robert L Koch: One thing to keep in mind with those is You know they are pretty susceptible to some diseases that help keep their populations in check. So just because you see them doesn't mean you need to freak out and spray again. You want to be scouting. In this case, we typically recommend looking at making decisions based on percent to foliation.

Robert L Koch: So again, going through that field getting a representative sample of plants kind of from throughout the field, and then looking at leaves from the top, middle, and bottom of the plant, and estimating the percent defoliation on those

Robert L Koch: and then averaging that percent to foliation

Robert L Koch: from those 3 different heights on the plants, and then across all those plants.

Robert L Koch: And we're still recommending the threshold of 30% defoliation during the vegetative stages and 20% defoliation during the reproductive stages of soybean you might be hearing some folks in other States recommending some lower thresholds for those reproductive stages down to 10 to 15. But,

Robert L Koch: We're not convinced yet that we need those lower thresholds in Minnesota. One important thing to keep in mind is a a lot of folks tend to overestimate

Robert L Koch: defoliation. So they look at a leave and you know, it might be

Robert L Koch: only 10% defoliation there. But it looks a lot worse than it really is, you know. So somebody might come away, you know, estimating that is 30, 40 instead of that 10. So there are some resources online that you can use to to train your I in estimating defoliation. And we've got those on the University of Minnesota Extension web page. You can find them in some other locations online.

Robert L Koch: And there's even some software out there. If you really want to get into it where you can or in it in an an app where you can snap pictures of leaves, and then it estimates the defoliation for you.

Anthony Hanson: Yes, we got a couple of questions coming in now, Bob. one is.

Anthony Hanson: Let's see.

Anthony Hanson: James is wondering about if they had fields of moderate. So I beneath the populations. Now, is there a way to account for the number of days? A Clint actually out in the field? And I think that's kind of baked into our thresholds a little bit, isn't it?

Robert L Koch: Yeah. Some, I think that kind of gets into what we sometimes talk about is cumulative a for days.

Robert L Koch: So it's kind of like, how degree days accumulate, how thermal units accumulate over the season. in this case it's how a fit pressure accumulates over the season. So

Robert L Koch: the number of if it's on the plant and factoring the number of days they're there.

Robert L Koch: the 258 at per plant threshold is actually

Robert L Koch: kind of back calculated from a cumulative day context. The challenges, I think a lot of people aren't scouting their fields necessarily regularly enough to have a good estimate of cumulative A for days. But

Robert L Koch: Those those thresholds are out there, and we've got that information, and some of the the online extension materials as well. I think it's

Robert L Koch: if if the folks are, if people are willing to invest the time in doing it it. It might be a better, potentially better approach for estimating the potential

Robert L Koch: stressed to those plants from the A fits, but it it is a little more intensive to do. So.

Anthony Hanson: Okay, couple of more questions coming in. One is asking about steward and set aside. So we talk about that a lot over in the alfalfa side, for I don't believe

Anthony Hanson: we have anything listed for that on Soibi Nathan, or other. So even in sex, that I can think of primarily. Yeah, I'm I'm blanking right now, I think. Is that one of the mixtures with diamide? let's say, Group 22 and docs a card?

Robert L Koch: Oh, It's not in our soybean neighborhood list, at least at all.

Robert L Koch: Yeah, I I I'd have to double check. I'm not sure if you might see that for maybe some of the caterpillars in Soybean.

Anthony Hanson: Yeah. One other quick question. Did you have the name of that leaf defoliation out

Anthony Hanson: on hand.

Robert L Koch: Oh, it's called leaf byte byte.

Anthony Hanson: I'm pretty sure. Okay.

Robert L Koch: I think most folks don't need that level of detail. you know, there are some different extension resources out there where it's just different pictures of leaves, so different levels of the foliation. And I I think that can get you a close enough ballpark estimate, and for a field to truly be at a threshold level, you know, be at the 20% or 30 that field's going to look pretty pretty ravaged.

Robert L Koch: but keep in mind that that soybean is a very resilient crop. it can tolerate, as we know, you know, fair amounts of stand loss early in the season, and then throughout the season, it it can tolerate or compensate for pretty substantial amounts of defoliation.

Anthony Hanson: all right, and we got just a couple of minutes left, Bob. So last question, how about

Anthony Hanson: new insects that have come in for soybean soybean galmage? And then also this new leaf minor that's coming as well. kind of what's the current status of those? And have we seen much for developments this year on those 2 species?

Robert L Koch: Yeah, as if all these other pests that we just talked about aren't enough. soy.

Robert L Koch: it's been in the State for a number of years. but mainly in the southwestern part of the State.

Robert L Koch: it. This year we were finding it again.

Robert L Koch: From what I've heard from my students, and in conversation with Bruce Potter. I think the numbers are appearing to be lower than they were several years ago, but I I think time will tell for this infestation. finding larvae in plants symptomatic plants that are showing, wilting.

Robert L Koch: so that's something to be aware of, but not something to over react to. Yet I think the

Robert L Koch: I can pretty confidently say the vast majority of fields in Minnesota will not need any kind of treatment for this past. We've only really seen heavy infestations in in a couple areas or a couple of farms

Robert L Koch: in the State, or lately just just one farm. And even on that one it's probably not necessarily at levels that would require treatment.

Robert L Koch: the other pest is a leaf mining moth. It's a a tiny little moth, and it's caterpillars live inside the leaves. This is a native insect that that feeds on a couple of native plants, and for whatever reason, in the last couple of years it decided to start feeding on Soybean. most of the research and scouting we're doing is down along the

Robert L Koch: Minnesota River Valley kind of between the twin Cities and Mankato. but we've seen it in some other areas as well. we've got some crop news articles, you know. Minnesota extension crop news articles that have some pictures about it. We've got a fact sheet.

Robert L Koch: So you want to look at the undersides of the leaves, and they make these little

Robert L Koch: kind of light colored blotches on the leaves where the the larvae are feeding in there, and kind of killing those tissues in the leaf, and as the caterpillars are largely get bigger. Then you can start. See the seeing the

Robert L Koch: spotting or tenting of the leaf from the upper side, and the the name that's been approved for this insect now is the soybean tentiform leaf minor.

Robert L Koch: it really likes the edges of fields and especially edges with trees.

Anthony Hanson: Yeah, so hopefully, we'll hear more about that one in the future, and maybe it won't be as much of an issue as could potentially be. But I know I I did hear someone describe that, you know. When you look at that kind of tenth look on the leaf. It kind of looks like either a popcorn or a rice puff, or something like that. yeah, it's kind of takes you by surprise a little bit when you do see that kind of puffed up leaf there. So it's pretty distinctive.

Robert L Koch: Anthony. One more. One more quick thing if I if I can get back to Soybean Galmage, if

Robert L Koch: anybody is aware of infestations. I would certainly

Robert L Koch: like to hear about it. We've got some different research projects going on, or we'd really like to get out and sample some more field. So if you're aware of sleeping Galmage infestations and soybean please reach out. Let us know.

Anthony Hanson: All right. Thanks, Bob, and thanks everyone for attending today's session on Corn agronomy updates. And so we've been insects with Dr. Jeff Colter and Dr. Bob Cook. Join us again next week at the same time

Anthony Hanson: for updates on diseases and soybean agronomy as well. There. So thank you, everyone. And we will see you next week again. We want to thank our support from Minnesota. So I've been Researched Motion Council and the Minnesota Corn Research Ocean Council.

Anthony Hanson: and that general support has helped kind of keep this webinar going very well over the last few years here. So again, thanks for that. All right, everyone. We will see you next week. Thank you.

Corn agronomy updates and preparing for soybean insects
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