Subscribe
Share
Share
Embed
Join the University of Minnesota Extension Crops team in addressing all your crop-related questions this growing season, from soil fertility, agronomics, pest management and more. We will tackle issues as they arise to help you make better crop management decisions this season.
Well, good morning. My name is Dave Nicolai with the University of Minnesota. I'm an extension educator in field crops. I'd like to welcome you today to today's Strategic Farming Field Notes program. We're happy you've joined us for this particular session.
Dave Nicolai:This program is entitled soybean and corn insects and thresholds on status for this this year, primarily talking about corn insects here. We also have Brett Arenz who's going to be on board here to talk about the Plant Disease Clinic. All of these sessions are brought to you by the University of Minnesota Extension and a generous support from the Minnesota Soybean Research and Promotion Council along with the Corn Growers of Minnesota Research and Promotion Council, with that. As I mentioned, our our special guest today is our University of Minnesota Extension, Entomologist, particularly in the in the corn area, Dr. Fei Yang. And then also our other guest today will be Brett Arenz, and Brett is the director of the Minnesota University of Minnesota Disease Clinic, and we'll be bringing both of those folks in here to talk a little bit about their activities and their programs and what's going on with some of the crops here in the state of Minnesota.
Dave Nicolai:So with that particular situation, I'd like to turn it over to doctor Faye Yang, and Faye is gonna give us a little bit of an overview in terms of corn rootworm and also maybe answer some other questions and so forth as we go forward. But it is that time of the year. So Fei, I'll turn it over to you. And if you have a couple of slides you'd like to share with the group, that would be good. And we'll talk about corn ribbon life cycle and management and some of the other things to think about this year as well as thinking about, you know, how that impacts next year.
Dave Nicolai:So, for that, it's all yours.
Fei Yang:Okay. Good morning, everyone, and thanks for introduction, Dave. So today, I would like to talk about some, like, management of the, like, corn insect pests, particularly, like, western and the northern corn rootworm. So today's session is a maybe a little bit different from, like, previous ones. So they've asked me to prepare some slides, but I won't go too much details.
Fei Yang:I just, like, give some, like, introduction and then do some overview over the these two species. Okay. So in Minnesota, we all know, like, that we have two major species for corn rootworm for management. So one is the western corn rootworm on the, like, left side of the picture. So you see these yellow and the black covers.
Fei Yang:Those those are western corn rootworm. And the right side is the the pale green one, so these are the northern corn rootworm. So these two species, they are in the larva stage, you cannot tear, but for the adults, it can be easily, like, differentiated. So for a western corn rootworm and these populations are most abundant in continuous corn. And for the for the, like, movement of the adults, most times, these, western corn rootworm adults, they want to travel long distance.
Fei Yang:So most of the time, you are managing local populations. Like, you manage your field. You're managing, like, the, like, the neighboring fields. And for resistance status, so right now, we all know these western corn rootworm nationwide spread resistance to the two new two old BT proteins, chorus three b b one and the chorus 34 35 a b one. And for northern corn rootworm, these are abundant both in continuous and the rotated cornfields, especially because of the extended diapause.
Fei Yang:And the insects, for the adults, they are more mobile compared to the, like, western corn rootworm. That means these adults can travel long distance. Sometimes you can find those, like, northern in other fields, in other hosts. So don't assume these be those like, if you see a lot in your fields, don't assume these are developed from your fields. These may travel from other fields, from your neighboring fields.
Fei Yang:And for resistance to BT, and recently, we don't have too many cases. That doesn't mean we have we don't have any resistance in field. So only two cases. One is in Minnesota, like a Mick Candy as in 2019 reported, and another one is in North Dakota. So if you look at the, like, the overall life cycle of these, like, rootworm, so the eggs laid by those adults during, like, September, They are staying in the until the early May on or June.
Fei Yang:So these eggs, they hatch, and these larvae will feed on your corn roots through, like, late May until sometimes, like, late July, depends on different locations. And whilst this, like, larvae feeding your corn, and if we don't have management strategies, so these roots will a bit prone, and then you will see larger larger plants in your field. And then become pupae, and these pupae, we are developing into adults. So most times, during, like, middle to late July and as long as, like, September, and you can see lots of adults flying in your fields. And these adults will lay eggs again in the soil year and stay over there until next season.
Fei Yang:So the most important thing for the management right now, I don't think you you can control anything, but from if you do scouting and, whatever you do right now is to predict the population for next year and what kind of management strategies you are going to use in 2027. So we encourage growers, like, to do, like, a scouting beetles. So we have two different ways. So why the whole plant starts? And then you can do, like, weekly scouting and using, like, a there are lots of different methods.
Fei Yang:And so this typically, like, we recommend a u shape and a 12 spots in each spot. You check, two plants. And then for the continuous confit, the stretch rate is about, like, one beetle per plant. And for rotated cone, so in Minnesota, we use a little bit higher, like, 4.5 beetles per plant. And another easy way you can do is just to go ahead and set set a yellow stick trap in the fields and change those traps area like a week.
Fei Yang:So we encourage at least, like, six to eight traps per field and make sure these traps, like I said, like, correctly and don't close to each other. Normally, we need, like, 50 to 100 paces between each trap. And currently, for the, like, a threshold for stick traps used across state is, like, two beetles per trap per day. But in Minnesota, sometimes we comment, like, four to six beetles per trap per day. So right now for management of this kangaroo worm, we have three typically management strategies.
Fei Yang:The first is crop rotation. This is the best management strategy. And most of the fields in our in our state are doing, like, rotating. So because, like, the can only lay eggs, like, typically, like, in the cornfields. So the for example, this year, right now, they are laying eggs in your cornfields.
Fei Yang:So if you do rotation next year to non corn host, like soybean, alfalfa. And once these larvae hatch, because the larvae can only survive on corn roots, and they don't have, like, food. So they will be cured. So next after next year, you rotate it back to Kong, so you will have no problems of the, like, rootworm pressure, especially for Western corn rootworm. And the second management strategy widely used right now is a BT trades, and we have different model of of BT traits.
Fei Yang:However, as I mentioned, because of resistance. So you will if especially for Western corn rootworm management, you will see lots of failures of the, like, a BT technology. And the last one is still good, but it depends. So for chemical insecticides, we can use in different ways. So we can do, like, a as planting insecticides, and then we can all you you can also use, like, a seed treatments.
Fei Yang:And right now, the high concentrations, like twelve fifty has been used from target like a corn rootworm, especially for those like low pressure management. And also you can use like a foliar sprays for adult control. So for crop rotation, as I mentioned, this is typically, like, used, like, in in Minnesota and in combat, like, in the soil, like, rotation for management. However, like, due to some, like, extended diapause and Western corn variants, and sometimes you will see one year crop rotation maybe not good. So we especially for extended diapause for Northern corn rootworm.
Fei Yang:And if you want to management, those extended pulse population probably need to do two years rotation. That means you do corn, soy, and probably another beet and back to corn again. So for BT traits management of conglut worm, so these are the old proteins. So we have CRAS three b b one. There are three different versions like m CRAS three a e, CRAS three one a b.
Fei Yang:They are same thing because once convoluted worm evolve resistance to one of these CRAS three, they have cross resistance to the other two CRAS3 b BT proteins. And the second mode of action is CRAS34, CRAS35, and right now renamed as g p p 34 and the t p p 35. And the recent one is IEI. We call it d v s I n f seven genes for management of the. So these b t proteins have been used as combinations in permitted b t cone, and then they can express at least the two different mode of actions for.
Fei Yang:And then these are some, like, commercial products with different BD proteins, like, in in the past few years. And the one thing I would like to mention, yesterday, I went to Benson to attend, a Bears, like, field day, and they have a new trait. They call corn rootworm four to deal with the widespread resistance of Western corn rootworm to all the CRE and the CRE 34, 35 ABO, proteins. So this is a new trait, they have, like, two new proteins and the one enhanced RNAi or DBSN f seven genes for management of based on this, like, internal, like, reports or experiments. So that's ConrootWorm four provide a very excellent management control for corn rootworm.
Fei Yang:So I will have some seeds to test the next year. So I will see whether this, like, product works very well in our, like, locations. So for the two new beta proteins, one is m p p seventy five a a, and the other one is v p b four. So according to Bayer, so this product will available during the 2028 season for growers. So last management is, chemical insecticides.
Fei Yang:As I mentioned, we have, like, a soil insecticides at planting. So the older one, like, capture, like, are forever because of resistance to. So sometimes you cannot see much effect efficacy using. And also based on my last few years, like, study in research station, the new group, like, 30, Neurisma, and Plinabulin, I didn't see too much effects for management over, like, the. But that that mainly they don't have effects in other places.
Fei Yang:So those data are just based on our locations. But for the as organophosphate, and the Yntax, those two works very well for management of the corn rootworm, especially at moderate a prejudice. And finally for seed treatments, as I mentioned, so only the high concentrations like 2,050 has been mapped either for cross algae or like a has been used for management of corn rootworm. And this based on our last two years study, they showed some efficacy at a low pressure, but at moderate or high pressure, we didn't see too much, like, effect for management of corn earworm to increase a year. I think that's all for my slides, but I still have of questions to discuss.
Dave Nicolai:Okay. Well, thank you, Faye. We don't have any, open questions, but we do have some prepared based upon previous calls that myself and other coworkers across the state have gotten. We were talking before about beetle counts and in the field in in trap. We know that people have been noticing and and probably finding beetles.
Dave Nicolai:A lot of those beetle counts are meant to help you determine what your management should be next year and the years following more so than an impact in in in this particular year. Now we mentioned before, I think you said, in rotated crops, you know, four to six beetles, it's it's typically pretty very high. What's the general feeling here in Minnesota about the need to spray or treat for, adult beetles, whether they're Northern or maybe Western Minnesota here as a control measure versus doing these other things. Any comments about that?
Fei Yang:So these, I think yeah. As I mentioned, you have two ways to do that. The starting is better for beetles, like a whole plant counts that takes a lot of time and another easy way doing yellow stick trap. So all these, like, all these two methods, I try to determine the population density or population size in your field. And what you do right now is to manage it for the next year.
Fei Yang:So as I mentioned, we have two lots of, like, the methods, right, crop rotation and, for the insecticides or BT traits, those must be used the next year. But if you want to control a bit of right now, so the efficacy based on not just ours, like, across other academics. So the man the efficacy of, foliar insecticides for spring beetles barriers. So the we we cannot see consistent, like, control because, like, beetles are very difficult to control. So the timing also very important.
Fei Yang:So you needed to know if if especially, like, your your field has a mixed population of Northern and Western, and you need to understand, like, the emergence sequence. So most times, the now the Western corn rootworm emerge about, like, one week earlier than now. That's first thing you need to remember. And the second thing, the males normally emerge almost, one week before females. So both for both Westerns and the Northerns.
Fei Yang:So when when you are going to do the spring for control of beetles, you are trying to kill the females. Right? So you need to make sure most of our fields are females, and, and, yes, especially for the, like, the mixed populations. For example, for the first time, you will see lots of males of Western corn rootworm beetles. And the second peak, you will see females of Western corn rootworm and the males of Northern corn rootworm mixed in your field.
Fei Yang:And the last is the females of the Northern corn rootworm because they have the two species that have, like, a one week differences, and the males and females have one week differences. So we need to timing very well, make sure these, like, populations in our field that you are trying to control are females. And, also, because of the northerns and the westerns, they can move from field to field, especially for northerns. So if you control your field, but in your neighboring fields, they don't do control. So these those beetles can fly to your fields.
Fei Yang:So it's very difficult to manage your neighboring fields. So control accuracy is still, like, be affected. So, normally, we didn't see too much, like, efficacy in our, like, field plots for the beetle control.
Dave Nicolai:Okay. I think that's that's a good point is that, going too early, you're gonna miss time, mixed populations, beetles coming in from neighboring fields that you can't really determine and and count on and so forth. So used as a management tool in and where this particular year, we found to be over the years very difficult. And some of these other methods, whether they're a a BT or a resistant or in terms of the hybrid itself, soil insecticides, etcetera, seem to be more efficacious, more effective, you know, in in in terms of that. So those are some of the things, with that.
Dave Nicolai:The, so that's that's what we have to do. Now the only other question that I know that Anthony Hanson and my coworker talked about is, you know, are they going to really affect pollination in in there in terms of that? There's a lot of pollen in the field, but we don't seem to be I don't know your take on overwhelming and affecting poor pollination by the amount of corn, if you're especially if you're doing whole plant counts.
Fei Yang:Yes. So so for if you if you see a lot of beetles, like, feeding corn silks. So, normally, if they don't, I maybe I remember the numbers are wrong, but it should be like if it's still, like, more than for the prawn, more than, like, zero point a half, Like, for the sea for the sea it won't affect too much for the, like, pollination. So if it's already past the pollination, so it's not necessary to kill those beetles. So the pollination won't be affected.
Dave Nicolai:Right. Certainly, when it's brown silk, they pollinated, you know, as well in terms of that. I think the only other thing I wanted to ask about is in in terms of, you know, anything you wanna mention about extended diapause, and that is especially on on Northerns. Years ago, we were concerned, not so much. But now again, is that something where they can skip that rotation and still be a problem?
Dave Nicolai:Is it just being effectively monitoring your fields to to manage that?
Fei Yang:Yeah. So for for the, like, extended our pause, so we see these problems since, 20 back to 2031, 2022 or twenty twenty twenty twenty twenty twenty one, 2022. And we see the most most situation, like, serious situation in 2023. And the 2024, it, like, becomes, like, a little bit of a quiet. And the 2025, we last year, we have lots of problems with extended parts.
Fei Yang:It seems that the Northern corn rootworm may extend the parts coincide with, like, the order, like, a number of years. So based on other states, like, a research, so almost a fifth if you have extended that pause in your in your in your field, almost 50% of the populations, we are do regular that pause, and the remaining one, we are do, like, extended that pause. But for the remaining half, like, 50% won't they they they are not, like, all them, they will go to extend their pause for two years. Some go two years, and some go, like, three years. So probably, like, thirty to forty percent will go two years based on Illinois data, and the remaining one will go like three years.
Fei Yang:And, also, I want I would like to mention based on research, so those extended diapause are inherited, especially sex linked with the females. So if you can can control females, so the extended diapause traits can be can can be reduced in your population.
Dave Nicolai:Certainly. Well, thank you very much. Faye, we can hang on. If you don't mind, we're gonna switch over to talk with Brett and see if there's any other last last questions.
Dave Nicolai:So Brett, if you wanna unmute yourself, I'll bring you bring you in. Brett is our director of the Minnesota University of Minnesota Disease Clinic, which is based on Saint Paul campus over in Stakman Hall. And, Brett, I believe you have a cover slide, so to speak, here. Not a cover band, but a cover slide. We talk about that.
Dave Nicolai:But this is the time of the year when people are out in the field making decisions on so forth. There's lots of different diseases, but it doesn't happen every year. Weather and environment make a big difference here. Some years we're worried about Southern rust, some years we we may not even have it occur or come up in this area, but there are other things to do that. So what are some of the services that you've been involved with the Disease Clinic that maybe help some of our producers?
Brett Arenz:Thanks Dave. So yeah, as you mentioned, we are the the plant diagnostic clinic. We're based on the Saint Paul campus, University of Minnesota. We essentially work on all types of plants except for turf grass. Turf grass is kind of a specialty diagnostic service.
Brett Arenz:There's a there's a lab in Wisconsin we actually refer people to if they're interested in turf grass. So, basically, everything else. I think last year, we had over a 180 different plant species that were submitted as hosts just to give you a range of the diversity. And, of course, that includes some of the important crop species in Minnesota, certainly corn and soybean. You know, I always tell people that, really, you know, successful disease management is impossible without starting with an accurate diagnosis, first of all.
Brett Arenz:Right? You have to know sort of what the main problem is to know how to be able to treat it. And even if, you know, treatment is is recommended at all or if it would be, you know, you know, waste of money or something like that if you're trying to manage something based on a a guess or something like that. We accept samples by hand delivery, which you can do coming to the Saint Paul campus, basically, right by the the State Fairgrounds. Our website is listed here, pdc.umn.edu.
Brett Arenz:If you're trying to find a map to how to get there and where the parking is. We also take samples by mail. For mailing samples, I really recommend, if possible, to submit whole plants. You know, I know that's not always possible, of course, when you have a, you know, like, a whole corn plant or something like that. Corn leaves typically tend to hold up pretty well in the male.
Brett Arenz:Soybeans, of course, it's usually good to get whole plants because, of course, oftentimes, you have potential foliar symptoms, which are actually caused by by root pathogens. And the only way to know sort of what you're dealing with is to actually be able to to look at the roots. Typically, for people sending whole plants in the mail, we recommend that they wrap the roots in plastic, but leave the aboveground part of the plant more open, maybe kinda loosely bundled in, like, newspaper or something like that. Certainly, you don't need to add any moisture because that it kinda ends up causing a mess by the time it it gets to us. And sending early in the week is good, so it's not gonna be hanging around in the you know, over the weekend in a post office or something like that.
Brett Arenz:We have submission forms. Providing a lot of information is really useful. You know, how long have you seen the problem? Are there other species affected? If there's a pattern to it, does it seem to be getting worse?
Brett Arenz:That kind of thing. We do charge for testing. Typically, fees range from 50 to a $100. $50 is kind of our base diagnostic charge. It covers a lot of microscopy and things like that.
Brett Arenz:$100 is more if there's, like, a virus that we need to test for that requires DNA or RNA extraction. Extraction, just requires more bench time in that case. If you are wondering, you know, what type of tissue is best to collect to submit, please send us an email, pdc@umn.edu, or give us a call, (612) 625-1275. Happy to help answer questions regarding that. As far as any, you know, particular pathogen in particular, we're kind of on lookout in the state.
Brett Arenz:Of course, red crown rot is a a disease of soybean that we first detected last year in Minnesota. So that's definitely one to be on the lookout for, one that's on our radar. And the first sample came from a a sample soybeans that was submitted to the clinic last August, okay, from Southwest Minnesota. But what's really curious about it is that it hadn't even been reported from Iowa at that point. So it seemed to sort of have either kinda gone under the radar in that state or totally skipped over it, but it also was reported in Wisconsin last year.
Brett Arenz:So it does seem to be kind of on the kinda northward push. As far as what to look for with red crown rot of soybean, aboveground symptoms are very similar to to SDS, sudden death syndrome, and also brown stem rot. You know, you're getting that interveinal sclerosis on the soybeans. The key thing to look for are what we call the red paresthesia that it produces near the crown of the soybean plant, and they'll look like little bright red dots, kind of the size of a of a pencil tip. So quite small.
Brett Arenz:I would recommend people get, like, you know, just like a simple magnifying glass, a hand lens, keep with you, will be helpful to to look for those. And sometimes those parathesia don't actually develop until a little bit later in the season, so you might start to see some above ground symptoms and see a little bit of reddening through near the stem, but you might not see the parathesia until a few weeks later even. So keeping an eye on that area of the field, maybe going back to it, checking for those. And, of course, if you, really need confirmation, you know, feel free to to send it into the clinic to get that.
Dave Nicolai:So, Brett, we've got a couple questions that came in actually while you were, talking about this. And one of them is a very general question, and it's and and it might be something you can find in a in a lot of soils depending upon, where it's at, horticulture or agronomic. The question is, in general, is verticillium becoming more prevalent in soils in Minnesota? And that might be anecdotal based upon your observations. And then I'll have you keep tabs on this because we'll just rattle them off here.
Dave Nicolai:The other the second question, are you getting many samples or seeing much for white mold this year? It's been pretty dry. And, and then I'll I'll come back and talk a little bit about aphids later with Faye. But let's just talk about those two briefly, and then I have one quick question on corn leaf submission. Okay?
Brett Arenz:Yeah. That's a good question. So, Dave, unfortunately, I don't know if I have the right sort of dataset to be able to tell you if verticillium is becoming more common. We are certainly detecting it year after year. Most of the verticillium we end up getting in the clinic actually is associated with tree samples.
Brett Arenz:So Right. Things like maples, you know, ash, things like that certainly can can pick it up. But we do, you know, see it on, you know, things like potato as well from time to time. So definitely something we can test for. It does have a very wide host range, which is why oftentimes when people see wilting plants and they, you know, look up briefly, like, wilting, you know, plant species of whatever it is, verticillium, something that pops up as a possibility.
Brett Arenz:So we do get that test request quite often. And in some cases, certainly that's that's what's going on. I think the second question is
Dave Nicolai:Yes. White mold. Okay. Prevalence of white mold, are we getting samples? It's a dry year, obviously, in a lot of places.
Dave Nicolai:Not always, but
Brett Arenz:Yeah. So white mold, you know, the Disease Clinic is an interesting, certainly, we are part of the biosurveillance network for the state and helping to monitor what diseases are going on, what's, certainly what new diseases are are being detected and things like that. But we are, you know, really sort of biased to, of course, the the types of diseases that are submitted to the clinic for for one thing. White mold is a disease that people oftentimes can can diagnose more easily themselves, you know, certainly finding the the sclerotia themselves. So we don't get a lot of white mold samples, I would say, even in a wet year, even when it's a very common disease just because it's a it's a pathogen that oftentimes people can sort of see themselves.
Brett Arenz:It's kinda like, you know, powdery mildew in in a way in that. It's a very common disease, but we don't necessarily see a lot of it in the clinic because people oftentimes can diagnose them themselves. So I'm not sure if I have a good sense of of how common this is. Yeah.
Dave Nicolai:It might be a little bit early too for that, you know, situation. It typically occurs a little bit later, but certainly we can test for it on it. I have a quick question here because I'm gonna go just a minute overtime here. But we always have a lot of corn leaf diseases and so forth. So this corn is now tasseling.
Dave Nicolai:Any recommendations if you're gonna send samples in, you say, I'm not sure what this looks like, whether this is a Northern Corn Leaf Light or something else. Anything about preparing corn leaf samples so they get to the clinic in decent shape so that you can make analysis. Any recommendations on particularly? You're not sending in a whole corn plant, but you're gathering leaves, etcetera.
Brett Arenz:Yeah. Corn is something where, you know, foliar diseases typically are actually on the leaf, and so you don't need to necessarily send the whole plant if you want us to test for those. We have seen, as you mentioned, a little bit of northern corn leaf blight, some bacterial leaf streak come into the clinic. Right. It has been kinda on the dry side, so I wouldn't imagine this is gonna be a hugely terrible year for corn leaf diseases.
Brett Arenz:But, of course, we'll, you know, see how the rest of the year kinda
Dave Nicolai:plays sample prep, though? Make sure that they get there. Any recommendations?
Brett Arenz:Yeah. Certainly don't add any extra moisture. You know, if if the leaves are kinda wet, maybe, you know, it was irrigated or it had rained, maybe even letting the leaves dry out a little bit before putting it in the mail, I think, would be good. I don't think you need to, you know, close it up in a plastic bag, maybe just sort of loosely bundle it. Because a dry leaf still is is pretty good for corn leaf diagnosis, so you don't have to be worried about that.
Dave Nicolai:Okay. Alright. Great. Thank you very much. Last question, Faye, I don't know.
Dave Nicolai:This is a little bit on the soybean side, but I think they asked question about whether aphids are out there and and it would be soy soybean aphids there and there. May or may not be. Anthony Hanson, I don't know if you wanna pop in here on Western Minnesota. Any quick updates on soybean aphids yet that you've seen showing up yet, or are we still a little early, or is this the time to look?
Anthony Hanson:It's the time to look, Dave. It's been pretty quiet. Our scouts out in Western Minnesota haven't found much for soybean aphids at least yet. Okay. At least quiet so far.
Dave Nicolai:But keep monitoring. And what's our economic threshold again?
Anthony Hanson:Two fifth 250 aphids per plant. That's trying to avoid getting to about six seventy where you actually get damage occurring.
Dave Nicolai:Per per plant. Okay. Alright. Well, we'd like to thank both of doctor Faye Yang from University of Minnesota Extension, corn entomologist, also Brett, the director of the Minnesota Disease Clinic and his operation there, good folks to to deal with. And if you can reach out to either one of those if you have a a particular questions.
Dave Nicolai:Well, thanks again for attending. I appreciate that. And with that, again, if you have other further questions, get ahold of us individually as we go through this, but we will be posting this information. So thanks again to both Faye and Brett and Anthony for your help, some of the organization, Andrew on the on the backside. Thanks again.
Dave Nicolai:Well, have a good day, and we'll be talking to you, down the road.