Insect pests are one of the number one enemies when it comes to planting. Without proper pest management, the infiltration of insects could easily lead to untimely deaths of plants, destroyed crops, and a diminished yield. Dr. Nick Seiter is a field entomologist and researcher with the University of Illinois, where he develops and evaluates management strategies for insect pests of field crops. In this episode, he joins host Todd Steinacher to discuss what to look for and when to investigate pest-related damage to your crops. Get valuable know-how you can use to protect your crops and your yields in this episode of The Yieldmasters Podcast.
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Let’s Talk Pest Management With Dr. Nick Seiter
This episode is about bringing a unique perspective on agronomic concepts that can reduce crop damage from insects. I would like to introduce our guest, Dr. Nick Seiter, Field Crop Entomologist with the University of Illinois. Welcome to the show, Nick.
Thank you for having me.
Nick, if you would spend a little bit of time, tell us about your background, what you do with the University of Illinois, and what led you down your agronomic path.
I’m an Entomologist by training. I’ve got a Bachelor’s, a Master’s, and a PhD in that. I grew up in Southeastern Indiana, surrounded by farms, not necessarily on a farm. I thought that entomology in particular but agriculture more broadly would be a good way to combine my interest with science, in getting outdoors, and in solving problems. I did my PhD down at Clemson University in the Southern United States, working on soybeans down there and an invasive pest of soybeans called the kudzu bug.
I had the opportunity to develop IPM recommendations for an insect that we had not previously dealt with before. That was a good experience for me. I worked at the University of Arkansas for 3.5 years as an Extension Entomologist. In that case, working in not just soybean but corn, cotton, and grain sorghum, I worked quite a bit in grain sorghum down there. I got a little bit of experience with rice and peanuts but probably only enough to be dangerous in those two crops.
I had the chance to come to the University of Illinois several years ago. I worked about 80% of my time in corn and 20% in soybeans in Illinois. That’s probably a fairly good representation of insect problems in the state. Corn rootworm has been our biggest insect problem in agronomic crop in Illinois for many years. That’s the one that I spend the majority of my time on. I’ve worked with a variety of pests in soybean including bean leaf beetle and stink bugs. I work on other test corn also, corn earworm and many others. I also have an extension appointment, so I spend a fair amount of time fielding calls from the public on that. Mostly corn and soybean issues. I got a call from a Christmas tree farm. I got calls from homes, I found this insect in my basement, too. I have bed bugs to goodness knows what. You get to keep up on a wide variety of different topics that way.
Thanks for that information, Nick, sounds like you have a really broad and depth knowledge across all pests, whether it be the field crops or non-field crops. I can appreciate that because I get a lot of folks who know that I work in ag and they pull me into garden questions or something like that. It’s always fun to try to stretch those thoughts a little bit. Nick, as we think about pests, specifically, maybe pests that feed on corn, at the end of the day, why does a pest want to attack a corn plant?
If you think about it on a large scale, we got about 11 million acres of it in Illinois. Something’s going to find a way to take advantage of that plant. When you have that much of a broad scale, any insect that does well on corn, if they can survive the temperature and the climate here in Illinois, they’re going to do pretty well in Illinois. What we find a lot of times when we make plants, in general, that are suitable for us, we’re usually breeding them for starch and oil content. For breeding them for sugar content in some other crops and in specialty crops. We often make these plants very attractive to different insect pests. There’s a wide variety of insects that will feed on corn. There’s a much smaller number that causes major problems in Illinois.
A few of those are fairly consistent, most of them are a little more sporadic. We have them ebb and flow a little bit over the years. In addition to just the food source, they have to have the right environmental conditions. They feed on each other. They have natural enemies that help regulate them as well and that leads to some of these ebbs and flows. The corns are a pretty attractive plant for an insect, especially when you consider how much of it we have in the state.
Don’t over-rely on any one single insect pest control.
I’m probably going to jump ahead slightly. We’ll come back and get to some other questions. You had referenced the corn rootworm. We’ve got a lot of corn but we also got a lot of lawns, ditches, golf courses, and football fields, they all have grassroots. What’s specific to a corn plant that a rootworm likes corn and not the other grasses?
We have a lot of that, the nutritional content as well as the size and architecture of that plant. There’s a wide variety of different characteristics of these plants that affect these host-plant relationships. Everything from the volatiles that plants produce to attract insects in, to the defensive compounds that these plants have. In this case with corn rootworm, it’s pretty tightly evolved with corn and a few fairly closely related plants. There’s a relatively narrow spectrum of grasses that corn rootworm can complete its development on. In Illinois, the only one that we have in an appreciable amount is corn. We don’t see development on other grasses to the extent that it matters.
It’s probably a good thing that we don’t have rootworms trying to feed on the roots of golf courses or football fields at high schools or anybody’s lawn. I’m sure there’s a pocket of the community that appreciates that it only attacks corn which makes it pretty challenging for us in the field to handle that pass. You referenced that some of the pests have different things that they like within the soil. There are some predators, the nutritional content of what that pest is getting, so pests are always evolving within the environment and they migrate differently. We were chatting about the Japanese beetle and how we don’t maybe why it migrates to the direction it does. It comes in very hot and heavy and dilutes itself. From a pest standpoint, what causes some of these migrations and what should people be watching for as they hear of new pests starting to come up in the media?
When we see these fluctuations in insect population throughout an area, it’s environmental conditions, not always but often it is. You get this build-up of various natural enemies, whether it’s a pathogen, a predator, or a parasitoid that will affect those. You probably saw it in ecology classes. As a kid, I saw this in a high school biology class or something where the prey goes up and then the predators go up and the prey goes down. You get an ebb and flow that way. Sometimes it’s that simple with insects. Usually, it’s far more complicated than that. Usually, it’s a variety of different combinations of environmental conditions and natural enemies, competitors for food that all lead to these outbreak cycles where you’ll have a fairly dramatic year.
We’ll call it a bad year for a pest like a Japanese beetle for instance. The next year you don’t see that with an insect-like a grape colaspis for instance that we see in parts of Illinois. It seems like about every 10 or 11 years at fairly high levels, a lot of times that’s related to soil moisture and having the right amount of soil moisture at the right time in the season the year before. There’s a variety of different conditions that can play dependent on the individual pest.
I’ve been working with farmers advising it at the field level for more than fifteen years. It seems like before the season starts, I always get the question, “Todd, what’s going to be our problem this year?” It always seems like there’s a problem that pops up. A lot of times, there is a difference, whether it be a particular weed, disease, or insect that pops up. There are these flows and the food source and all these other pieces that play into it. We might not know what’s going to pop up until it gets here. It’s just very interesting to, from my standpoint, advising growers on we don’t know what that particular pest is going to be until it gets here.
My job would be a lot easier if I knew what was coming in the winter as far as, “This is going to be the big insect in summer 2022.” If I knew that next winter, I could plan for it. I could have a lot of good things ready to go. They continually surprise us. If you think about all the variability that you have predicting the weather, which is how well we do at that, then you add in the ecological variability, the interactions with other insects, and the timing of those weather events. There’s just a lot of complexity out there that it’s rarely as simple as, “It hits such a temperature, so we’re not going to see this particular pest.” It usually doesn’t work that way.
Nick, I’ve got a follow-up question for you on that. We’ve got a lot of pests overwinter here in Illinois or any states across the country. We always talk about survival rates. Whether it be the bean leaf beetle, rootworms, or whatever, in my mind all these pests are relatively in the same areas and where they’re going to overwinter at, whether it’s the soil, residue, somewhere. What causes a certain population to have a higher survival rate than the other population within their same pest?
You have a combination of factors there. One, you have the innate ability of that insect in whatever its overwintering life stage is to tolerate certain temperatures. The temperature that they’ll tolerate varies quite a bit. As you might imagine, a lot of the insects that we find more in the Southern United States, their cold tolerance might not be as high as an insect like the corn rootworm for instance, that survives very well through all but the most extreme winters that we see here in Illinois. You also have the overwintering behavior of those. That can depend a little bit on the life stage. If you have an insect that overwinter, say an egg for instance or as a pupa, they’re not going anywhere necessarily. They’re going to bury themselves or hide, whatever it may be. That’s it. They’re there. The wrong temperature comes at the wrong time, they’ll die.
You have other insects that might overwinter as an adult might be able to seek out a more favorable overwintering location. Stink bugs will do this for instance. That’s one of the reasons when you have stink bugs overwintering in your home, if they’re in a windowpane, for instance, they might get enough heat over the winter to become active. In February, you start having stink bugs flying around your home like I do with the brown marmorated stink bug from time to time. I have an older home that they’d like to find their way into.
In some cases, you’ll get combinations of those factors and the soil texture even can play an impact on that. You know that if it’s an insect that overwinters as a pupa, it might be able to work its way deep enough into lighter soils to survive. Whereas if you get into the heavier soils, it might not make its way quite so deep and might not be able to make it. You’ll have these pockets where that insect has been able to overwinter but in other areas, it will not be.
It’s not just one factor. It’s a variety of different factors that lead to those different insects being adapted to different climates. In Illinois, we see pests that don’t overwinter here that are still successful pests. Potato leafhopper, for instance, in alfalfa. Corn earworm, we get very little corn earworm survival over the winter here in Illinois. Yet, we see them every year in sweet corn, eventually, and infield corn as well, though it’s much less of a problem in that crop. A wide variety of different factors at play there.
A follow-up on the earworm one. From where I’m located at that gets blown up and can cause problems where it doesn’t overwinter, does that mean where it does overwinter there’s enough population for it to rebuild itself again to cause problems in that area and then flush more populations up? Does it have that much of a reproductive cycle?
Where that insect does successfully overwinter down in the Southern United States, you see a couple of large differences. One, the populations are just quite a bit higher. In Arkansas, we call them bollworms. It feeds on cotton bolls, corn, and sorghum. You call them a sorghum head worm if it’s in sorghum. Some people call them soybean podworm if they’re feeding on soybean pods. In Arkansas, we have that insect as a pest of soybean. Here in Illinois, it’s pretty rare to get them as a serious pest of soybean. That’s all about the abundance. When you have more generations in that area, the abundance is much higher.
The other thing you see is they become a problem earlier in the season. In the Southern United States, you can follow them from crop to crop. They’ll start out on corn, complete a generation on corn early, and then following that generation, they might move into grain sorghum, soybeans, or cotton. In fact, they’ll move into all three of those crops. You start to see them at different crops following that fruiting structure. The whole process starts much earlier because they’re able to successfully overwinter further South. For us, we don’t start seeing corn earworms until we might start seeing the mods here. This is about the time of year where we’re seeing some of those mods coming into different parts of Illinois. Southern Illinois probably have already been seeing them.
Nick, I like to take some deeper dives into a couple of pests that a lot of the AgriGold folks out there tend to run across. The first one I like to talk about is very specifically the corn rootworm. Over the years, we’ve seen this population spike, go up and down. We find pressures out there but it seemed like we’re at a yield-limiting situation or standability but then you still had these pockets, these heat maps, we’re sampling and have problems all across the greater Midwest. What are your thoughts on the current pressure of rootworms as it stands for this growing season? Where can we expect that to go?
What we’ve seen over the growing seasons, early indications are it’ll be this way this 2021 as well, is that it’s low compared to historical levels but it’s creeping up. It’s particularly creeping up in areas where we have a lot of continuous corn. We haven’t seen in Illinois over the years near the issues with rotation-resistant corn rootworm that we had in years past. There are still issues out there but not to the same extent. We’re starting to see those populations build more in the continuous corn area. If you go up the heatmap, the red spot in Illinois right now. It’s especially up in Northwestern Illinois and in Northern Illinois in general, we have a lot more continuous corn than we do as you work your way down into Champaign–Urbana, where I’m located. There’s a little bit of continuous corn but not near to that scale. It’s primarily one-to-one rotated corn and soybean down here.
Understanding where the insect is is really important.
As far as the factors contributing to that population decline, the availability of pyramided Bt traits has been a big reason for that overall decline. As you start to see more resistance issues with Bt in Illinois, that’s probably contributing to that uptick that we’ve seen over the years in overall population. Another thing we’ve had going for us and against the rootworm is weather conditions. You mentioned flooding conditions. When we have saturated soils, and especially standing water, during the period of time when those eggs are hatching, especially when the eggs are hatching and when you have small larvae out in the field, that hits that population pretty hard. In 2015, my colleagues talk about it a lot where we had a lot of standing water in late May and early June when those rootworm beetles were hatching. It knocked the corn rootworm population back considerably. We haven’t had it as widespread in years but we have had wetter springs and wetter early summers than what the historical average is. That contributes to suppressing the population as well.
From a rootworm standpoint, there’s the Western and then the Northern. From your standpoint, is one more prevalent in certain areas or more resistant to some of the practices or the traits out there? What are your thoughts on the two separate pieces out there?
It’s a good time to talk about Northern corn rootworm because over the last few years, that’s one in particular that we’ve seen more of in Northern Illinois, especially than we had in previous years. For years, Western corn rootworm had become not just the dominant species, it’s still the dominant species in Illinois throughout most of the state, but it had gotten to the point where it was almost the only species that we thought about throughout most of Illinois. Over the last few years in Northern Illinois, we’ve seen a few more Northern corn rootworms. In fact, some pretty big problems were caused either primarily or in large part by Northern corn rootworm in addition to Western.
You have a few differences in those populations that are relevant to management. One has to do with rotation resistance. In Illinois, Western corn rootworms have been our primary rotation-resistant species. Western corn rootworm overcomes crop rotation by laying eggs in soybean and other non-host crops. If you’re in a situation like in Champaign County, Illinois, where maybe 95%, 90% of the landscape is rotated corn and soybean, then laying your eggs in soybean is a pretty good characteristic to have. There’s a high probability that soybean field is going to be corn the following year.
With Northern corn rootworm, it can also get around crop rotation. It does so through an extended diet pause so those eggs remain in the soil not just over one winter but some of those will hatch after 1, 2, 3, and 4 winters. It hedges its bets a little bit that way and those eggs that hatch after two years, if you’re in a one-to-one corn-soybean rotation, will then hatch into corn. That’s a big difference between those populations. You also see that the susceptibility to Bt traits is a little bit different. They both from day one were susceptible. Northern corn rootworm was a little bit less susceptible to 34/35 in particular when it was first released.
Those proteins were designed for both species but with a special eye towards Western corn rootworm which has been the more economically important species for many years. Now, we have resistance to at least Cry3Bb1 and Cry34/35Ab1 in both populations confirmed. With Western corn rootworm, we have resistance to all four Bt proteins that are available confirmed somewhere. That doesn’t mean they’re resistant to all of them all over but there’s resistance to all four of those proteins present somewhere in the country in that incident.
As it relates to the diet pause, 1, 2 years, and then they’ve evolved into laying their eggs in soybean fields, have those habits always been there? Has that population realized, “There’s something attacking us and we need to evolve on how we how we manage our life cycles and our eggs to where they evolved to do that?” Is that something that’s always been that way?
The way this selection pressure works, it acts on a trait that’s already present in the population. Usually, a trait that’s present in the population at very low levels. It’s not causing the insect to mutate. It’s selecting for variability that’s out there. In the case of Western corn rootworm in particular, if you think about it, crop rotation was recommended as the primary control for Western corn rootworm for about 100 years. We had about 100 years where we didn’t treat for Western corn rootworm, in particular, in first-year corn, because that’s how reliable rotation was as far as preventing an egg lay in that crop.
If you think that it took 100 years for that trait to emerge at any meaningful level, what that suggests is that in the wild-type population, the frequency of females that were a little less picky on where they would lay their eggs. That’s ultimately what that trait is. Instead of laying their eggs on a host crop, they’re laying it not just in soybean but they’ll lay it in oats, wheat, or pretty much anywhere where there’s bare ground. To some level, they’re still laying a lot of their eggs in corn. If you think about how many generations of Western corn rootworm it took, it gives you an idea of how rare that trait was in the wild-type population, which makes a lot of sense, because even if you’re a rotation-resistant Western corn rootworm larva, you can’t survive on soybean roots. Every egg that hatches in soybean is still going to die. Every single one of them. You get no development on that crop whatsoever.
Something as fundamental as the host-plant relationship of that insect takes a long time to overcome that. In part because it’s selecting for traits that are already out there, in that case, it’s a trait that was out there at an extremely low proportion of the population. The higher the proportion of that resistance trait when a control is first introduced, the sooner that you’re going to see resistance. When we look at something like Bt corn or insecticides, for instance, there’s plenty of examples of insecticide resistance as well in corn rootworm. That hasn’t taken 100 years. It’s taken maybe 5 to 10, depending on the protein. The prevalence of that trait in the population still wasn’t high when those were first introduced but it was higher. That’s how that selection pressure works. It’s going to act on a trait that already exists, even if it’s a trait that’s incredibly rare.
It’s a good way of putting it. It makes sense once you explain it. You hit on some of the proteins, the Bts and the Crys that we’ve seen some resistance from a trait standpoint where we’re getting ready to see industry-wide. Maybe SmartStax PRO being released here. There’s still talk of a Duracade in the market. What are your thoughts from a trait standpoint with some of these new pieces coming to the table? One, from an effective standpoint, and how can we manage that so we’re not in the same boat 5, 10 years down the road where we just blew past it again and now, we’re trying to find the next silver bullet?
As far as how to manage it, you alluded to it there. What we don’t want to do is over rely on any one single control. Every time we do that, we lose it. Every time if we rely on one thing, if we use glyphosate for all our weed control for 10, 15 years, whatever it was, we know now how that story ends. It’s the same with insects, it might take a little bit longer but if we rely on the same control over and over again, we’re going to lose it. With any new control that comes in, we want to make sure that we keep some variability in the overall system.
One of the best tools we have for resistance management in corn rootworms is crop rotation. That’s one of the most effective ones that we have. In part, because of how few different modes of action we have, at least on the trait side in corn. It’s not as if you can rotate pyramided Bt hybrids and rotate modes of action. We have four different proteins and two modes of action. Every trait package that’s out there includes one of those modes of action. Regardless of what you rotate with, you’re still exposing that population to that one mode of action. That’s that Cry free mode of action that 3 of the 4 proteins share.
When we look at SmartStax PRO, with that RNAi trait, that will introduce a third mode of action. It’s not a Bt, it works completely independently of that, which is good. It will still include as a pyramid, those two Bt proteins that are in SmartStax. With that new trait package, in particular, it’s going to be another tool in our toolbox. It’s going to help. It’s still important to preserve the activity of those Bt proteins. Introducing variability into that system in terms of how we’re controlling it is the most effective way that we have to manage that resistance.
One of the reasons crop rotation helps us out so much, if you think about what I said, all the eggs that hatch into soybean, they’re going to die if it’s a Western corn rootworm egg. From an industry standpoint, when there’s a problem field, when there’s a field that’s showing unexpected damage on a pyramided trait hybrid, their first recommendation typically is next year, rotate that field to soybean. You’re not going to wipe out that population by doing that. Those beetles are going to move but they’re going to lay a lot of eggs in that field they emerged from as well.
Typically, they’re going to lay more eggs in that field they emerged from than they are in the surrounding fields. Even if you’re in a highly rotation resistant population, they’re laying eggs in soybean, they’re getting out of that field quickly and laying eggs elsewhere, they’re still going to lay a lot of eggs in that field they came out of. You’re still killing a lot of individuals by rotating that field. By having soybean out there in the environment, it does at least delay that process. You’re not selecting the same individuals in the same field at the same trait over and over again.
That’s where when we find resistance emerging. It’s no coincidence that I believe every new instance of Bt resistance that we’ve had, every new protein, the first place that we found that has been in continuous cornfields. Often, it’s been in long-term continuous cornfields where they’ve been exposed to the same trait in the same field year after year. That’s a situation we want to avoid where we can to avoid that selection pressure on those populations, which becomes very intense when you have the same trait in the same field year after year.
There’s a lot to think about when you’re making a selection. A lot of times, we might get tunnel vision focused on this year, but from a farmer standpoint and longevity, we almost have to look at this from a holistic approach. “What is our plan for the next 2 to 3, 4, or 5 years?” “How is my decision this year going to impact everything else?” There are a lot of moving parts playing into it. You did hit one piece on SmartStax PRO bringing a third mode of action. Since that’s not similar to the other ones, what’s our risk from a resistance standpoint? With that being new, but yet, we’ve got a lot of resistance already built out there. Will that hurt us? Do we need to be more cautious with this? What are your thoughts?
When they get the right conditions, and the natural enemies aren’t there, that’s where you see these outbreaks.
My understanding is that the risk of cross-resistance is low. Meaning the risk of resistance to Bt carrying over to that is relatively low. At least from a mechanistic standpoint that’s a good thing. The risk of resistance is there. We have survivors on SmartStax PRO from day one. It’s not something that comes in and eliminates adult emergence from those fields. It dramatically reduces it but does not eliminate it. The risk of resistance is out there, it’s the best way to put it. It’s something we have to protect, especially when you consider that it’s coming in as a pyramid with two other Bt proteins. Even if on day one that it’s released that RNAi trait is not compromised, those other two proteins, there’s already resistance alleles, resistance traits out in the population to those. It’s something we need to protect from day one if we want to have it for the long term.
Let’s change our conversation a little bit. I want to dive into stink bugs. I’m seeing a cultural shift in some areas where we’re not working as much soil. We’re going more maybe no till, strip till corn, and starting to see more populations of stink bugs. A lot of growers are happy to go out whether they go out proactively and put insecticide with their herbicide, or weed and feed. If they don’t, seeing a large population, they have to go out and do rescue treatment.
In some situations years ago, I can remember being in the field. I was literally there on Sunday and there was no problem. By Tuesday, they invaded this whole field. The corn was up high enough to where when it was sticking its sucking mouth part in there, it was damaging growing points and damaging what was eventually going to be the ear. Come harvest, it was a train wreck. As we make these cultural changes, what’s a recommendation specifically from a stink bug? Why are those populations becoming more of a problem?
Why it’s becoming more of a problem and why we’re seeing that more often could be a number of factors. One, we’re seeing more stink bug problems in general across crops in the Midwest than we have in the past. That’s in part depending on where you’re at in the Midwest. In part because of the brown marmorated stink bug that’s come in, that would be more especially out to our East, and then just shifts in the climate. We’re seeing more stink bugs earlier in the season than we used to and more survival over the winters and that kind of thing. We’ve noted increased stink bug populations in both corn and soybean.
When you look at tillage, there is an opportunity in some cases to have some overwintering in that residue that can get some early season populations. With stink bugs in corn, there’s a couple of periods of time where they can cause a tremendous amount of damage to the plant. One is what you referenced when they’re able to feed on that developing ear when it’s still within the whorl. Several whorls before tassel, if they’re willing to feed on that developing ear down in the plant, they can cause a tremendous amount of damage.
The other time that they can cause a tremendous amount of damage to corn is if they’re able to feed on the seedling itself. They’re able to feed on that seedling right as it’s emerging within the first couple of whorl stages, they’ll cause significant stunting of those plants. It doesn’t happen all that often but when it does happen, it’s severe. You get some severe yield losses from it. While it’s an uncommon situation in Illinois, when it happens it’s serious. In between those two windows of time, if they feed on that whorl, they’re going to put a little mark in there. It’s going to be 4, 5, 6 strips in a row. It’ll look tattered. It resembles corn borer damage, for instance.
That kind of shot hole feeding across the leaf but it’s more tattered than that. It’s usually a little bit discolored. That damage itself is cosmetic. That’s not going to lead to yield loss but if you have a lot of that in the field, that can suggest that you have a fairly high stink bug population. That’s one of the big things I would look for when you’re deciding whether you need stink bug management or not. If you’re seeing a lot of that, go out in the field and scout. See if you can find them. They are difficult to scout for.
My colleague at NC State where they’ve been seeing more stink bug injury in corn has some threshold guidelines on that. He has a threshold for early whorl and he has a threshold for late whorl. They are difficult to scout for. They do things like hiding on the other side of the plant. You’ll walk up to them and you can watch them sneaking around the stalk. It’s fun to watch but it also makes them very difficult to scout for. Looking for that damage, while the damage itself, that damage to the foliage isn’t yield-limiting. If you have a lot of that, it is an indication that you have stink bugs in the field and that you should investigate that further.
Some pests can have multiple generations within a given season where one generation is going to feed early, one late, bean leaf beetles. If a grower finds that they had a lot of stink bugs, maybe they didn’t go out and treat but they knew they had a lot of pressure out there. Say they got an adjacent soybean field to this cornfield, will that population that was feeding on the corn V6-ish come over into the bean field, or is that a different generation that’s going to attack that bean field later at R4?
They do get up and go. They’re fairly mobile. What stink bugs are adept at doing is they follow reproductive growth, in general. When they feed on those corn plants early in the season like those whorl stage corn plants, it usually means there’s nothing else around that’s in reproductive growth that they can feed on. What they want to feed on are fruits and seeds. When they start to enter soybean fields, it tends to be later on in the season in Illinois. It tends to be at the beginning of R5 when you have that seed starting to develop in there.
Between the time you might be seeing them in whorl stage corn, and then whether there’s been another generation or not in these stink bugs depending on species, they’ll go through 2 or 3 generations per year in Illinois. Whether it’s the same generation or a different one, they’ve had a lot of time between them to move from crop to crop. Not just field crops, but fruit crops, trees that put out seeds, and grass weeds. If you want to see a lot of stink bugs, go out into a grassy meadow that’s headed out and sweep. You’ll find loads of different stink bugs species. That’s one thing that makes stink bug management fairly challenging, is they do follow the reproductive growth in these different crops.
From my standpoint, there are green ones and brown ones, there’s the new one coming up that you hear a lot more about. What’s the difference between all three of them? Is one more of a problem than another, we’re seeing them in our fields?
The type of damage that those three do, if we’re talking about field crops here, the brown stink bug, the green stink bug, and the brown marmorated stink bug is the same. They’re going to do about the same type of damage. When you’re accounting your thresholds, for instance, in soybean, a stink bug is a stink bug from that stretch. If you go further South, they have an insect called the red banded stink bug. In that case, that’s a different animal. That’s much more damaging. They operate on a lower threshold with that insect. In terms of the damage they do, it’s similar.
What we see with them, when you see them in corn, it’s almost always brown stink bug. Sometimes it’s others, brown marmorated will get in there, especially when the ear has come out, but most of what we see in corn in Illinois is going to be brown stink bug. Green stink bugs are a little less picky. You’ll see them in soybean and on a wider variety of plants. With brown marmorated stink bugs, they have a wide host range. They feed on a wide variety of different fruit and vegetable crops, which probably waters that population down a little bit when you get into corn and soybean country here in Illinois.
One thing that’s been noted about brown marmorated that’s somewhat unique if you’re scouting in row crops and especially in soybean is that when they’re startled, they have a tendency to drop. They’ll drop from the canopy onto the ground. Whether you’re sampling with a sweep net, a shake sheet, or visual sampling, they can be much harder to find because of that, in some cases. Those are our three main pest species.
One of the big differences between those species isn’t in field crops, it’s in fruit and vegetable crops. Brown marmorated stink bug can be a devastating problem in fruit and vegetable crops to a greater extent than the greens and the browns. Part of the reason for that is their wide host range. The other thing they do that all these stink bugs have a habit of but they seem to do in particular is they’ll feed and that feeding site ruins a fruit. It deforms. It causes a cat facing to where you can’t market that fruit in the fresh market.
They’ll then hop over to another fruit and feed on that one. They’re not going to sit on the one fruit and ruin it and leave the others alone. Every time they feed in that specialty crop market, they ruin the fruit. That’s where the damage from stink bugs can be severe, less so in corn and soybean. Thankfully, in corn and soybean, it’s just another stink bug. It’s not a good thing to have, but certainly something we can manage.
I learned a little bit that the brown stink bug is similar to a possum when it feels threatened. It curls up and hides and plays dead. It’s good to know there are other things out there that act like a possum. It’s good information. If you’re out scouting and you’re doing a sweep net or you’re out walking, you might have some false indicators that you don’t have a problem. You probably need to open that canopy up a little bit more from a soybean standpoint and look at the soil and see what’s down there to give good insight. I’m glad you called that one out.
Damage to the foliage isn’t yield-limiting. It’s an indication that you have stink bugs in the field and that you should investigate further.
My colleagues out in Delaware and Maryland and Virginia have some guidelines on scouting for brown marmorated stink bug, specifically on how to go about that in soybean.
Those are some good resources to check out. Nick, I wanted to switch crops. We’d like to talk about soybeans. I know you got a lot of crops in your toolbox that you take care of. I’ll keep it simple. We’ll just talk about soybeans next, not fruit trees or anything like that. A lot of times, we still have conversations from soybeans bean leaf beetles. To me, learning that bean leaf beetles, early on, had two generations that were fighting. The ones that get us early on, and the second generation that comes and gets us R3, R4, or R5 that could be causing pod damages. From your standpoint, let’s dive into bean leaf beetles and how they interact with growers and fields.
In 2020, in my part of Illinois, in particular, we had quite a bit of pod scarring, where they’ll scar up that pod. Oftentimes, as that pod is maturing, it’ll cause a gap to form in there that allows moisture and pathogens in, and it’ll damage that seed. It’ll damage quality but it’ll also damage yield in some cases by causing that seed to rot. With bean leaf beetles, when we have that occur, we don’t have it occur in large numbers every year as we did in 2020. It’s somewhat uncommon to have it at the levels that we had in 2020. We see a little bit every year.
That’s going to be the bigger issue that the bean leaf beetles caused. In the spring, they tend to be the first insect that we see and the last insect in soybean. It’s the same generation, that overwintering generation. They tend to go into the last remaining green soybean fields. That’s where they concentrate themselves, is in those late-maturing beans before they go to their overwintering sites, which are ditch banks, leaf litter, and soybean residue. They’ll overwinter and then in the spring, the earliest planted beans, they’ll concentrate in those when they emerge.
In those early planted beans, we tend to see them, and they’ll tear those leaves up. Usually, tearing those true leaves up that the actual impact of that damage on soybean yield tends to be minor unless you have bean pod mottle virus in that system. If you’ve not dealt with bean pod mottle virus before, if you don’t have a history of it in your area, the impact of that feeding early on tends to be minor. Soybeans take a lot of defoliation without losing yield before the reproductive stages.
The first generation that develops during the season is going to get ready to start coming out. That’s one that we tend not to see as much of. They’re out there, and they’ll feed on soybean. That tends to be a little bit more watered down. They are mobile as adults. They’ll get around from field to field. In Illinois, you tend to have a million acres of soybean. You would be hard-pressed to drive a mile without finding a soybean field in Illinois. When you have all that soybean out there, that population has plenty of areas to go. It waters that population down. Whereas early in the season and late in the season, early when the other fields haven’t emerged yet, and late when you’re one of the last handful of fields to mature, you concentrate that population in that area.
That’s when we see the high numbers. The defoliation, it’s uncommon for bean leaf beetles to do enough defoliation by themselves to impact yield. Typically, if we see defoliation impacting yield in Illinois, it’s a situation where we’ve had in the same field. Several defoliators come in and take out that leaf tissue over a period of time. When you get them feeding on the pods like that, if you get that in high numbers, that can be a serious problem like it was here in 2020.
Nick, with that, you’d referenced the high populations that sparked in 2020. I was right on the edge of some of those populations. What caused that big thrust to go? Was it because the overwintering in that environment was so good or just all the stars aligned? What are your thoughts on that? Why did that region within Illinois explode with problems?
It’s probably a combination of issues. It’s another one of these that if I knew the exact combination of conditions that caused them to be a problem, I’d be able to predict the next one a whole lot better. A combination of adequate proper soil moisture, a high population to begin with so success during that first generation. Perhaps success during the overwintering generation as well building that population up and then not having the pathogens, the natural enemies out there working on that population at the right levels. You get a combination of those environmental conditions and of natural enemies working on that population. When they get the right conditions and the natural enemies aren’t there, that’s where you see these outbreaks.
A follow-up on the natural enemies. From a bean leaf beetle standpoint through the growing season, what would be an example of a natural enemy of a bean leaf beetle?
For bean leaf beetles, specifically, you have some pathogens that will attack them. I believe a parasitoid wasp that goes after them as well. Certain predators will eat them, too, but predators tend not to be all that particular with a lot of our pests.
As far as winter survival rates, I’ve seen some data from Iowa where they have some quadrants throughout the state where they can predict a little bit based on how harsh the winter is or could be, what that could look like as far as knocking down some populations. It seems like bean leaf beetles are sensitive to an overwintering piece. What are your thoughts there?
They’ve been using that model for several years. They feel like it correlates pretty well, especially with that early generation. Early in the season, seeing high numbers of beetles in the seedlings, they feel like it correlates pretty well with seeing that. I ran the model in Illinois in 2020 to compare it to them. As you might imagine, since we’re to the South of Iowa, our survival based on the model throughout the state was quite good, especially in the Southern half of the state.
You were getting up into the Northern tip of Illinois before you had a lot of overwintering mortality working. A part of the reason probably that they’ve used that model more than we have is that more of their state is sitting in the range where you can have a pretty big hit on that population from the winter. We have that sometimes, but the average winter in Illinois is going to leave most of those bean leaf beetles alive.
To dive in that a little bit deeper from an air temperature, soil temperature standpoint, what temperature is that threshold that a bean leaf beetle would not survive, or maybe the duration of that temperature? What’s an environment, from that standpoint, would it not like to survive from?
The accumulation of below-freezing temperatures is what that’s based on. It’s almost like an anti-degree day accumulation for that model. It’s based on the average temperature, how far below freezing it gets, and the duration of that. You’re accumulating those below-freezing temperatures. I would have to look back at the model to know exactly what that duration is. It’s not a situation where, for instance, you say, “I hit negative twenty. That means they’re toast.” It’s not just about how low it gets, it’s about how long the temperature stays low. That’s for the model.
That’s predicting an average. When you look at the microclimate where these beetles live or where they’re spending the winter, there’s a lot of other factors that are going to play into that. If you get, for instance, a heavy rain event or you get a lot of moisture out there before it freezes, that’s often going to be harder on those populations than if you have a lot of snow cover. If you have freezing rain, that can be harder on those insects and other insect populations that are sensitive to overwintering. It’s not just the temperature that is having that effect, but with that model, on average, you can make a pretty good estimate of overwintering survival based on the accumulation of freezing temperatures.
Nick, I’m going to pick your brain on one last pest. It’s the soybean gall. I know it’s not impacting everybody. There are certain pockets across the US that has some pressure from it, but it is one that a lot of research is looking at. A lot of news articles and publications are being brought to awareness from it. If you could, let us know what your experiences are with it, and what environments or geographies that this could be a pest?
One of the best tools we have for resistance management in corn rootworm is crop rotation.
Fortunately, my experience with it so far is entirely academic. Learning about it from my colleagues, especially in Nebraska and Iowa, who’ve been dealing with this over the last years in a pretty bad way in some areas. I’m in Illinois, we don’t have it in Illinois. We’ve looked for it in Illinois. We sampled quite a few counties in 2020 in Illinois to see if we had this insect and we weren’t able to find it. Where this is causing problems, it started in Eastern Nebraska, it’s where it was first noted and it spread to Western Iowa, and then it’s in South Dakota, Minnesota, Missouri, and possibly other states. The real epicenter of that damage is still in Eastern Nebraska and Western Iowa.
It’s a fly, it’s a midge. The larvae live in the soybean stem behind the epidermis, and they’re feeding behind there cause that plant to die prematurely. It tends to be more severe on the edges, which at least in terms of finding this insect is a good thing. It’s hopefully going to be a little bit easier to find. The symptoms of it, my understanding, resemble something like sudden death syndrome where that plant is dying before it should be dying before the plants around it die. You then take that plant, you cut the stem open and you peel the epidermis apart in particular, you’ll see these little tiny fly larvae, these little tiny maggots. The older maggots are going to be orange, and they’re going to be curled up.
One of my colleagues in Iowa refers to them as orange slices. They looked like a little orange pearl and there will be quite a few of them. There might be dozens of these larvae within that plant. What’s unique about soybean gall midge, it’s one of the most fascinating things about it to me. This is an insect that’s new to science. They wrote a scientific paper describing this species after it was discovered in soybeans in Nebraska. That almost never happens. When we had the soybean aphid as an invasive species, for instance, we knew that exists. We knew it fed on soybeans in Asia. They were able to determine quite quickly, at least the general region where that came from. It’s the same with kudzu bugs, brown marmorated stink bugs, and with these other invasive species we’ve had over the last years.
With soybean gall midge, we don’t know if it’s invasive and if it was on one host and made a host jump over to soybeans several years ago. They’ve been reporting problems with this for 3 or 4 years or so, but when they went back and talked to some of the people that were affected, they were seeing it at low levels for several years before that. In terms of how it got here, how it came to be an issue, we’re not sure.
One thing that my colleagues in Iowa, Nebraska, in the Dakotas, and elsewhere, they’ve hit the ground running on this insect, learning a lot about it in a hurry. The situation now might be different from the situation as I learned it before. My colleagues are largely developing management recommendations for soybean gall midge from scratch, from nothing. It’s a concerning situation that way, the good news is they’re putting a lot of effort into this. They’re learning more and more about this insect all the time. Learning the basics of its life cycle, learning where it overwinters, how far it moves in a season, how to kill it. All these are basic questions that they’re trying to answer.
In my own geography, and it’s similar elsewhere, especially in the states that are on the periphery of that area that’s affected, understanding where this insect is, is important. We do ask our soybean farmers or crop advisors to learn how to identify this insect and the symptoms. The symptom is plant death, so it’s something that’s probably going to catch your eye anyway. Learning how to identify this insect, and if you find it, contact someone in your area, either the local agronomist, the extension person in your area, or the State Department of Agriculture. In Illinois, and I’m sure in other states as well, if we do have it here, we want to know about it so that we can begin to address it so that we can understand the impact that it may be having. My hope is that it’s not going to get to Illinois, or if it does, by the time it gets here, they’ll have already solved it where they’re dealing with, but it’s been a tremendous issue for those folks over the last years.
Nick, it goes with the title of the show, for growers striving to hit higher yields across their farms, corn or soybeans. In these pockets where they do have potential pressure with it, we are building a robust potential crop. As I understand, based on where this pest lies, there isn’t a lot of proactive treatment. It’s more of, “I know I have the problem, I can adjust or alter harvest, so I don’t lose yield from harvest standpoint,” is that correct?
The management recommendations on this, they’re struggling to come up with a solution to this particular problem, but that is ultimately what we’re trying to do. We’re trying to protect you. We’re trying to protect the yield potential that’s out there in those fields. Whether it’s gall midge or some other insect pest, we don’t want them coming in to take that away.
Essentially, the potential risk of the grower is if it is working there on that stem, at some point, we could have a stamped stem. If we wait too late in the season, environmental factors, weather plays into it, too much pressure, that’s where the risk is to the farmer is, correct?
With gall midge, the risk to the farmer comes from the death of that plant. It’s dying before it can fill that pot out. It is reducing yield potential that way. With an insect like the stem borer, we’re trying to get into the field in time to prevent lodging when we get into situations where we have lodging. With the gall midge, my understanding is it’s killing that plant early enough that it’s preventing that plant from filling out its seeds properly.
Thanks for the clarification. There are so many things that are attacking these crops that it’s hard for a grower or even agronomists to stay up to tune on what’s going on out there. With the internet, text messaging, videos, and podcasts, it seems like there’s a burst of information. It can be overwhelming to sift through everything to make sure we’re staying up on our game to make sure we’re not overlooking something. The value is there’s a lot of things that could attack our crop, that means there is value in being in our crop from a scouting standpoint. Whether you hear about it or not, you can see it in your field to know there’s a problem and then you can potentially go address it. That’s where the value is.
You got to be out there scouting crop. What’s happening in Champaign, Illinois is not what’s happening down in Milford and it’s not what’s happening up in Freeport and everywhere in between. You got to know what’s happening on your farm and in your fields.
I’m going to jump into a different category slightly, but I’m going to bring it back to this. The growers we work with within the NCGA contest, Corn, there are some other smaller ones from a soybean standpoint. A lot of folks say, “There’s no way I’m going to hit 500 bushels of corn.” That might be accurate in your own environment. The folks that are involved in the NCGA contest and striving for that spend more time in their fields and have a better pulse of what’s going on in those fields that they can make these, whether it be proactive or reactive decisions. That comes back to a scouting standpoint.
If we do have pests that we may or may not know we have problems with because we changed a cultural piece, maybe the winter wasn’t as harsh, or we’ve got less saturation early on, the more time we spend in our field, we’re going to know more what’s going on out there. It doesn’t always answer the questions. It tends to sometimes ask more questions, so you have to go find more answers, and it can be overwhelming. That’s where it is, to be out there understand what’s going on, build your network of advisors. Working with local seed agronomists and extension folks. There’s a wealth of knowledge out here, we just got to build that network. Nick, as we wind down this episode, I would offer it up to you if you had any final recommendations or suggestions to growers as they finish out this crop or even as they start planting future crops honing in from an insect pest standpoint.
The big one is what we discussed. I can’t emphasize it enough. You need to be out there and know what’s going on not just in your area and in the region, but in your particular field on your particular farm. Get out there and scout and know what issues you have and what’s affecting your fields in a given year.
Thanks, Nick. To wrap up a little bit, Nick did a great job. He presented a lot of good information for us on how to understand environments and how that can influence pest populations, whether it be temperature or moisture. We just got to be in tune with what’s going on. Even though we’ve got some new proteins coming out or mode of action rather, from a rootworm standpoint, SmartStax Pro, we still need to be vigilant on how we’re using it and be good stewards to it, so it lasts longer.
At the end of the day, if I could understand your message good, Nick, it’s respect the biology that’s going on out there within the pest. The populations and how they can change, and we got to respect the potential for resistance. If we start having widescale resistance across all of our tools in the toolbox, there might be a time where we don’t have any tools in there. At the end of the day, be respectful of the biology, the insects that are out there, and how it interacts with our crops. We got to make good decisions. With that, Nick, I appreciate you being on. For everybody out there reading, thanks and I hope you tune in next time. Thank you.
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About Dr. Nick Seiter
Dr. Nick Seiter is a field entomologist with the University of Illinois. Dr. Seiter develops and evaluates management strategies for insect pests of field crops. His research includes developing economic decision-making tools, identifying natural enemies of insect pests, and assessing insect control methods for their effectiveness and fit within management systems. His overall goal is to provide management recommendations that improve the economic returns and environmental profile of insect management practices.
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