Corn and Soybean Pests!
Today, our session again is brought to you by UOM Extension and also support from the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council. And our session today will be on corn and soybean pest update, including corn rootworm and soybean aphid. I'm Liz Stahl. I'm an extension educator here out of the Worthington Regional Office, and we have we welcome doctor Faye Yang. He's our extension corn entomologist, and doctor Bob Cook.
Speaker 1:He's our extension entomologist, does a lot of work with soybeans. So with that, I am going to turn it over to Faye, and then we'll bring it over to Bob afterwards too. But, again, if you have any questions during during while they're talking, please put those into the q and a box. So, Faye, I'll turn it over to you. Okay.
Speaker 2:Good morning, everyone. As introduced, I'm Faye. I'm the co entomologist at the University of Minnesota. And today
Speaker 1:Sorry. Can I inter do we have the recording going? Oh, it is recording. Okay. Sorry.
Speaker 1:Never mind. Okay. So
Speaker 2:as so today, I would like to talk about some major, like, coins in the past. So the first one, I think, like, the most important one in Minnesota is the rootworm, like, a complex. So in Minnesota, has, like, a western rootworm and a northern rootworm, especially, like, in the south area and the middle area. You have, like, overlapped populations of these both of these species. And the one thing I would like to emphasize this year, I think in lots of, like, rotated cornfields, and then we see some damage.
Speaker 2:And this is because of, like, extended our pulse. So as we know, like, most of the kangaroo worms, lily eggs, and these eggs will go diapause during wintertime and hatch in the spring, and most of these will hatch in the spring, like a regular diapause. However, for some populations of northern conglomerate, these eggs, they won't hatch, like, this year, and they will hatch, like, two years or even three years or four years later. So, like, in last year, I mean, the eggs laid in 2023, they didn't, like, hatch in 2024. So this year, lots of, like, populations of northern corn rootworm.
Speaker 2:These eggs hatch and cause lots of, like, damage in rotated corn fields. And the the the little cone fields for the, like, what's the percentage? We don't know currently. However, based on previous studies, there's only, like, small, like, problem in if we, like, back to, like, 1961, only, like, zero point three percent in Minnesota. So that's first reported.
Speaker 2:And then, like, subsequent studies in South Dakota, they found, like, up to, like, forty percent, and the later, like, in Illinois, they found, like, these kinds of percentages, various, like, from fields to fields ranging from, like, 14 to 51%. And currently, we don't have, like, any, like, specific data to support, like, Minnesota population. But based on those studies and we think at least, like, half of the populations of the eggs, they will hatch, like like, in the first year and the remaining one, they can hatch, like, two years or three years later. And, currently, we didn't find any pop like, populations resistant to BT for Northern Congruva. That means the BT technology is still very effective for management of Northern Congruva.
Speaker 2:So if you have extended that part populations and if you just do one year rotation and you can think about, like, using, like, BT trades. So for those, risk fears and you have huge populations of Northern Kongruo. But if you do, like, two years or three years rotation, I think you don't need to rely on, the BT traits as as you I mentioned before. So most percentage of the eggs of Northern Kongruo worm, they only have one year and two years like a, oh, like a dipole. And if but a a little bit different story for Western Congruhum.
Speaker 2:And then these Western Congruhum populations, they don't have, like, extended pulse. So they only have one one, like, And, also, the resistance problem to BT in, like, a western control room is widespread. And if you found a lot of populations in Minnesota, like, in Moore County, in Martin County, they showed, like, a heavily record resistance, over the, like, a western to different BT traits. And even, like, if you have heavier population, the newest, like, I and I technology, like, it's not that very effective. Because, like, compared to the those BT traits, the I and I is right, like, fast killing, for those, like, insect pests.
Speaker 2:So for other coin insect pests, I would like to touch is, like, about, like, stock borrowers. So this is the first time also, we call it common stock borrower. And then we found, like, this year when we do the scouting for, like, and we found a lot of the age, especially the first, like, three or four rows. You have lots of, like, damage or, like, a stock bricks. And at the beginning, I thought it was, like, a European can borrow damage.
Speaker 2:But later, we split the coin, and we found, like, it's another species. It's common stock borrow. So later when you do the scouting in the field and especially for the, like, the ages, the first the first few rows, and if you see those kind of damage. So don't, like, think about it. It's like recognize it as a European can can borrow damage, or it may also caused by the common stock borrow.
Speaker 2:So that's something new. And, also, we found that, like, those, like, common stock borrow, they are resistant to the BT traits. Even you plant, like, a BD which contains those lab doctor, active BT proteins, and you can still suffer great damage. And, previously, especially if you relay on the, like, a BT traits table, those BT trace table says those, like, lab doctor active proteins are still effective for management of common stock borrow. But based on this year's observation in several fields in Martin County, Moo County, and we found lots of fields.
Speaker 2:Even you planted with, like, a lab doctor active proteins, you still have some damage. So we collect a huge population in one field, in a b t in a b t fields, and we found a product especially for the lack of field age, we found, like, 60 to 70% damage. And it'd easy to collect more than 120 larvae, and we try to test them to make sure these populations are resistant or not. And I know, like, recently, lots of people have, like, a with, like, a chuami worm infestation. So those chuami worm populations, actually, it's not like a local population They migrate from the Southern States, and they will lay eggs, especially at the beginning of the eggs in the grass area.
Speaker 2:And if you have, like, cover crops, so they have, like, a high risk. And this mouse we are lay eggs in those cover crops. And then later, when you do the, a weed control or terminate those cover crops, those, like, insects, we are moved from those, like, fields to like field crops, the corn fields. So the true armyworm populations is very, like, difficult to predict, and it depends on what's what's the population migration population here. It typically take, like, a thirty to forty days, to develop.
Speaker 2:But if you wanted to know the location of the Chuan population, so we we have, like, a project supported by Minnesota Congo Conguro Association, and we use, like, a family traps to detect how many populations that we have come from the Southern States. And with those kind of, like, numbers, and that you can rely on, like, degree days and to predict how long this kind of migration populations labia develop to lobby and especially late in star lobby. Those those are the major stages causing, like, severe defoliation, your cornfields or, like, in your, small grain fields. And, also, if you wanted to use some like, if you have the, like, results to set up some light traps because these army worms, they are noctuity, so they can be easily attractive to the lights. And they also you can rely on those kind of traps to predict the populations of the, like, a true army worm.
Speaker 2:And in Minnesota situation, probably, we have, like, typically, like, two generations, and most of the damage, occur during, like, June to July. And then this year, we saw lots of, like, damage of chuami worm in the, like, fields. So do you have any questions? Yeah.
Speaker 1:Oh, yeah. Question about with, well, the true armyworm, how long do you think you have to monitor for that? Like, how long will they fly up? Because they're they're coming from the South because I am just trying to look as, you know, producer. You know, what point do I need to stop?
Speaker 1:Can I stop worrying about, you know, them migrating up? You know, when would they when do I no longer have to worry about this?
Speaker 2:So, normally, we set up a light trap, the thermal traps, like, during, like, late April, early May, and that that that's that's probably the first generation. And those first generation, they were becoming damaged, like, as I mentioned, in thirty, you know, about thirty days. So that's about, like, the, the June time. And then you can still set up because, like, if you if you know those kind of, like, insects in that area, because based on the first trap and then those, like, mouse can develop to the second generation and alleviate damage, like, in July. So I think, like, about, you can set, like, the traps during, like, May to, like, late June, so it should be good enough to predict the populations.
Speaker 1:Okay. Okay. So then later on in the season well, I mean, there must be a point where corn is no longer really affected by armyworm or because then we've getting more questions and a lot more interest about your army, especially with, you know, people being more covered crops and things like that.
Speaker 2:Yeah. Especially for the early stage earliest early planted crops. So for early planted corn, probably you are at risk. But when, like, in July, most of the corn are in Tesla stage, so that should not be, like, a big concern for corn growers. But a little bit would be, like, a major concern for, like, a hay grayers and also, like, a small corn growers.
Speaker 2:So because those populations especially for those armyworm, those lobby, they're highly mobile. So they can, like, match in larger group from this field to that field just in one night can defoliate all your fields. But if you plant, like, sweet corn, probably, it's also a challenge during that time. So do, like, scouting or monitoring over the population is very important, especially for those ages field age. So most of the population, are migrate from other field to this field.
Speaker 2:So pay attention to your aid.
Speaker 1:Oh, thank you. Yeah. Anything did you wanna share anything about corn borer at all too today? Or Yeah. For issues with that, you know, how are how are things looking there?
Speaker 2:Yeah. For European corn borer, so I I I I don't have too much to, like, share, but just some recent, like, research in our lab, not from the field. So we did detect the resistance populations or resistance genes in both Minnesota and, Wisconsin areas, not just in one location, in multiple locations. So that means resistance to one of the cryogens is a wider spread, like, around, like, landscape just at least in Minnesota and Wisconsin.
Speaker 1:Okay. That's not what I wanted to hear. But Yeah. So we will do
Speaker 2:some yeah. We will do some further test to make sure because right now, most of the PT countries, they have multiple proteins. And these populations for resistance, we just found resistance to one PT protein, but, the other proteins may still work for control of the, like, European can borrow. We will have some update later.
Speaker 1:So big thing would be to make sure that you know, like, what traits you're planting out there. Would you recommend people kinda switching around traits? Is is there much possibility to do that? Would that help with resistance managers for, you know, with corn borer and corn rootworm too, you think?
Speaker 2:Yep. Yeah. Yeah. Because as as I mentioned, for European combined, that's only one protein. So almost all the, like, traits in the market, they have multiple BT proteins.
Speaker 2:So you don't need to worry about right now for control over European Corn Borough before resistance is widespread.
Speaker 1:Great. Alright. Well, thank you, Faye. And, again, if anybody has any questions, please pop those into the q and a box. But with that, looking at the time here, I will switch it over to Bob.
Speaker 1:And if you wanna give us an update of from the soybean insect side here.
Speaker 3:Sure. Thanks, Liz. So for soybean insects, you know, soybean aphid remains our our most important insect across the state and into into the neighboring states. It's been kind of a slow year so far for soybean aphid. You know, I think we can find aphids in pretty much any soybean field out there, but populations in most fields are still very low.
Speaker 3:You know, we're seeing maybe on average 10 to 20 aphids per plant in most fields. However, some fields are getting a little higher. We are seeing some fields with around a 100 aphids per plant, not very many fields with that many aphids. Some of those observations are coming from Angie Peltier and Anthony Hansen who are collaborating with folks in North Dakota to survey
Speaker 1:Well, I think we lost your audio, Bob. I think you muted there.
Speaker 3:Sorry. Yeah. So Anthony and Angie are performing this survey across Western Minnesota and working with folks in North Dakota, and that's where, you know, they are finding some fields with about a 100 aphids per plant. I think Jan Kanodel and her team in North Dakota observed a field with around 400 aphids per plant. But, again, that that's kind of the rare situation right now.
Speaker 3:Most fields are are still very low, you know, 10 to 20 aphids per plant. Remember, the threshold is 250 aphids per plant, and that's the point again where we should start lining up the insecticide application. You know? So that's the trigger point to prevent the population from getting to those higher damaging levels. So even though populations are low now and have been low, you know, up until now, don't count out soybean aphids.
Speaker 3:If you look at the weather forecast, we're gonna have some pretty hot weather through the remainder of this week. But if you look over the next week and a half or so, temperatures are gonna looks like they're gonna be in the low to mid eighties, which is pretty comfortable for most of us and pretty comfortable for the aphids. So they could be reproducing very rapidly, at those temperatures. So I would definitely recommend scouting your fields, doing so on a regular basis, you know, especially now through August because, you know, even if you've got one of those fields with only ten twenty eight if it's per plant, that could change fairly rapidly.
Speaker 1:Well well, Bob, that's a good thing that you bring up because too because, you know, I was at FarmFest yesterday too, and, you know, there's people that were talking with us, and they're they were, you know, needing to make an application, you know, of a fungicide at this time because they had disease issues, but they had low level of aphids out there. And they're like, well, I'll just throw on the insecticide to you know, because it's I'll just make one application for that. But, you know, there's risks with that too. Right? You know, can you just kind of elaborate a little bit on that?
Speaker 1:Like, why why would we not wanna just throw something in there when we have a low population?
Speaker 3:Right. Yep. Yep. So those low populations. Again, when talking about low, it's, like, well below that threshold of 250 aphids per plant.
Speaker 3:And just to make sure there's no confusion there, that threshold is at trigger point to line up the application. It's not where we're getting that economic damage yet. You know, at that level of aphid infestation, we're not even getting any measurable yield loss. So with those low populations, you know, if you went through and added in an effective insecticide, you're probably gonna kill off those aphids are there, but there's no guarantee that those few aphids that are there were going to reach damaging levels. I see more and more fields where populations increase to 50, a 100 aphids per plant, and then they kind of flat line.
Speaker 3:Right? There are a lot of different factors out there, natural enemies like predators, parasitoids, fungal diseases that can help keep the aphid populations in check. Not all infestations will outbreak and reach damaging levels. So you could kill those aphids that are there if you mixed in that that cheap insecticide, if it's an effective insecticide. But remember, lot of those cheap insecticides that people are thinking about using are pyrethroids, and we have widespread resistance to the pyrethroids in the soybean aphid.
Speaker 3:So in that case, if you're, you know, spraying a field that has pyrethroid resistance, that pyrethroid probably isn't going to do anything to the aphids, but it will kill off all the natural enemies. And if you kill off those natural enemies, any remaining aphids will will have a free for all. They'll be able to increase their populations without anything keeping them in check. Know, so just hearing about these early applications make makes me kind of nervous because we are actually seeing situations in some of our experiments where treated plots with pyrethroids or even some of the mixtures of pyrethroids with neonicotinoids, you can end up with more aphids than in plots that you didn't spray. And that's probably, you know, kind of this classical pest resurgence scenario where you kill off the natural enemies.
Speaker 3:Those pests can have a free for all. More and more of these the more pesticide applications we make, the more pressure we're putting for development of resistance on these populations. And then financially too, right, if we're spraying an infestation that maybe would have never reached damaging levels, we're probably not getting a benefit from that.
Speaker 1:So you could make the worst problem that you didn't have before, basically. I I just think that's such an
Speaker 3:important investment to get
Speaker 1:out there.
Speaker 3:You know, of these people who are putting in these these early sprays, tank mixes with a cheap pyrethroid, sometimes they're having to come back and spray again because they're they're getting those outbreaks later because they took out the natural enemies.
Speaker 1:That's that's a great point. Great point. And and you mentioned neonicotinoids. Like, what if somebody used a seed treatment? What are you seeing with that?
Speaker 1:Have those been helping us out? And and are you concerned about following up with a neonic foliar application if they used a seed treatment?
Speaker 3:Yeah, so you know the neonicotinoid seed treatments can be very effective for soybean aphid. The question is when are the aphids coming in and how much that insecticide remains in the plants. So if you've got fields that are kind of historically colonized early by aphids when they're coming into the field getting on those plants and the concentrations are still high, when the neonic concentrations are still high in the plants, it can have an effect on those aphid populations and probably provide a return on investment. But I think most of our fields, aphids are coming in after that insecticide concentration has petered out in the plants. I think you also mentioned, you know, the concern about if if you've got neonicotinoid on the seed and then you come back in later with the foliar application of a neonicotinoid, that makes me kind of nervous in terms of resistance management because remember our soybean aphids, like all aphids during the growing season, are reproducing clonally.
Speaker 3:So that genetic stock of aphids there is getting exposed multiple times, probably consecutively, to the same insecticide group. Right? So you get aphids coming in, colonizing the field. They're getting exposed to the new neonicotinoid from the seed, and then you got multiple clone clonal generations being produced, so kind of the same genetics there. And then they're potentially getting exposed to the neonicotinoid a little later in the season.
Speaker 3:So maybe not the best situation in regards to resistance management.
Speaker 1:Great. Great points. And, you know, you mentioned a little bit, you know, like, some of the like, the pyrethroids can be more of a broad spectrum type insecticide. There's some more that are more selective. Do you wanna share a little bit about that?
Speaker 1:Sure. Yeah.
Speaker 3:So I guess before the selective insecticides, though, just to remind folks that chlorpyrifos is available still now. Right? There was kind of this regulatory roller coaster where chlorpyrifos, which a lot of people think of as Lorsban, you know, it it was available. It wasn't available. It was available.
Speaker 3:And where we're sitting now, to the best of my understanding, is some chlorpyrifos containing products are available, Kind of the traditional Lorsban product is not available, but there are other chlorpyrifos containing products, and those are very effective against aphids. You know, there there are some other concerns about, you know, the high level of toxicity to everything else from from that product, but it is very effective for aphids and spider mites. But if we're thinking in terms of integrated pest management, and we wanna try to integrate natural enemies of predators, parasitic wasps into our management plans to get that natural pest control. Selective insecticides are an important tool, and I think that's what you're referring to Liz, where we've got products like Transform, which is alfoxiflor, Civanto, which is flupirodifferone, and, Sefina, which is a fitopyropin, and all three of those products work well against the aphids and are relatively less toxic to the natural enemies. So you can spray your field, ideally take out the aphids, and leave, the natural enemies there to provide control of, you know, any new aphids that might colonize the fields.
Speaker 3:Remember that when we get into the, you know, August here, sometimes we'll get aphid populations developing wings, and then they can redistribute themselves within the field or even between fields. So if if you've got a field that, you know, maybe you've lucked out through the early part of the summer and there haven't been many aphids there, that could change really quickly because you might all of a sudden get your neighbor's aphids developing wings and finding your field to be a real nice spot to to invade.
Speaker 1:Well, and that's a great point too as we're getting here into well, we're in August. We're gonna be in the later August here too. At what point, you know, again, we talk about the thresholds and stages of soybeans. You know, when when can people kinda just stop worrying about eaf? It's, of course, we're kinda in the hot time right now, but you know?
Speaker 1:Yeah. When can we stop worrying about that?
Speaker 3:Sadly, we can't stop just based on the calendar. The aphids and other insects aren't paying attention to our calendars, so we really gotta think about plant growth stages. That threshold of two fifty eight if it's per plan is generally recommended through the r five growth stage. You know? So we wanna be scouting on a regular basis through r five using that threshold at 258 if it's per plant to decide when to spray.
Speaker 3:Once we get into r six, things get tricky. Bruce Potter, Ian McCray, you know, from a number of years ago, I think they had some data suggesting that very high populations of aphids can cause some yield loss in early r six, But that gets a lot trickier to make those decisions because, you know, you're getting so late in the season. You could push into that time period where, you know, the the plants are no longer gonna respond. You're not gonna get a return on investment if if, you know, if the those pods and seeds are getting too too developed in the plants. You know, you might start running up into pre harvest intervals.
Speaker 3:But, I mean, I think the fortunate thing that, you know, that Bruce and I have talked about over the years is, you know, if you're scouting on a regular basis using that threshold through r five, you should hopefully be able to prevent those tricky situations in r six. Right? You know, you'll ideally be able to catch things before they get to that point that late in the season.
Speaker 1:Right. Good point. And we did get a question here too. They're just wondering, you why are aphid populations low this year? Is it the weather, you think?
Speaker 1:Or
Speaker 3:You know, I suspect yeah. I I'm thinking it's the weather. You know, we've had some very strong rainfall events, you know, lots of rain, wind, things like that, and and we know that that can take a toll on the soybean aphid infestations, infestations especially early in the season when the canopies aren't closed. Those open canopies don't provide very much protection to the aphids so they can easily get knocked off the plants, fall to the ground, and once they're on the ground they don't stand too much of a chance of getting getting back up the plants. They could get easily picked off by predators or just end up starving down there.
Speaker 3:So in addition to the the rain and wind from the storms, I think, you know, some of the high temperatures that we've had, we've had quite a few days, you know, well into the nineties this summer, and and we know those high temperatures can slow down aphid population growth. So, you know, my best my best guess is that's been working against the aphids. But like I said early on in our conversation here, you know, weather conditions seem to be lining up pretty nice over the next week or so for aphid population growth. Right? You know?
Speaker 3:So low to mid eighties. Again, that that's good aphid growing weather. So I really recommend you you be scouting your fields on a regular basis because things could change fast in the next couple
Speaker 1:of They're scouting. Yeah. And that brings up too we do have some links here in the chat. Just go on to the field notes links for today. We have a number of links there, talking about, you know, soybean pest management, corn, insect pest management.
Speaker 1:Bob, I think you mentioned too you're looking at putting out an article here soon about, you know, some updates on, you know, management options for soybean aphid too. Is there any last comments that you wanna have before we wrap up for the day?
Speaker 3:Yeah. So in the meantime, until we can get that article up for soybean aphid, I I think, Liz, you were gonna post a link to an article from last year, which should still be pretty relevant with some general scouting recommendations, insecticide options. We'll update that and and get something else posted, but in the meantime
Speaker 1:Great.
Speaker 3:Folks can look at that. Do wanna mention quick, we are finding more soybean gall midge this year popping up in a few additional colony or counties around the Twin Cities. We recently found it in Ramsey County, Chisago County, and Dakota County. So I'm saying this not to scare people to start spraying their field. It's more of an awareness thing.
Speaker 3:Something to be on the lookout for. So if you're seeing plants wilting and dying on the edges of the field, take a closer look. Look at the base of the stem, see if you see those kind of characteristic darkened lesions on the stem. If you see that, peel those stems open and see if you see the bright orange larvae. I would definitely like to hear about it.
Speaker 3:If you're seeing soybean gall midge in, in soybean fields, we're really trying to figure out how widespread this thing is and hopefully, trying to find some additional research sites so we can do the research we need to give you all some, recommendations for managing this pest.
Speaker 1:Good. And and like I said, those links will be in we've got, like, one page of links, so you should find it on there. We did get a quick question here. What are the pros and cons of Indigo z z c x?
Speaker 3:Indigo z c x?
Speaker 1:Yeah. Indigo z c x?
Speaker 3:Yeah. So that's pretty commonly used for soybean aphid management. It's it's one of the mixtures of a pyrethroid and a neonicotinoid. It's gonna give you the broad spectrum control. You know, it'll definitely historically, it's done a very good job on soybean aphids.
Speaker 3:It should work well on, you know, quite a few other labeled pests in soybean. My concern is back to 2018, 2019, we're seeing the control from Indigo slipping in some of our efficacy trials at Rosemont where it was kind of providing intermediate levels of control, not the very high levels of control that it had previously. And last year, in our efficacy trial at Rosemont, we used a different mixture of pyrethroid and neonicotinoid, and the the product name is slipping my memory now. But with that product, that's one of the situations where we actually had more aphids in the treated plots than in the untreated plots. So the concern there is, you know, there is a pyrethroid in there.
Speaker 3:Lots of aphid populations are resistant to the pyrethroid. Pyrethroid, so if you choose to use that, you could be going in half broken, so to speak, with half that product not working, and then the neonicotinoids themselves as foliar applications alone historically have been kind of inconsistent in their for their control of soybean aphid. If you think about products being used for soybean aphids, there aren't many, products with just a neonicotinoid. You know? So I'm kinda guessing it was a combination of the resistance and kind of that hit and miss control with the, the foliar neonic that didn't knock the aphids down as much as we had hoped, but did wipe out the natural enemies so then those remaining aphids could increase faster in those plots compared to the untreated plots which still had lots of natural enemies feeding on the aphids.
Speaker 1:Alright. Great. That makes sense. Yes. Yes.
Speaker 1:Thank you. Faye, is there anything any parting comments you wanna add here too before we wrap things up for the day?
Speaker 2:I I think that's all for me. Yeah.
Speaker 1:Okay. Alright. Well, we thank you you both very much for participating today, and thank you everyone who joined us today as well. Again, thanks to the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council for helping sponsor this program. Again, there'll be a really short survey when you log off today.
Speaker 1:We do value that input
