Soybean Aphid Alert & IPM Update
Good morning again. This is Bill Hutchison with the IPM program, Minnesota Extension Service, University of Minnesota. And we're happy to kick off another podcast today with our primary guest, Doctor. Bob Cook, who's an Associate Professor of Entomology and Extension Entomologist with U of M Extension. Also joining us today, we have Dave Nicolai, who's the coordinator for the Institute for Ag Professionals, University of Minnesota Extension.
Bill Hutchison:So Dave, thanks again for joining us. Before we get started, Bob, why don't you take a few minutes just to introduce yourself and tell us a little bit more about your background and how you got here to University of Minnesota.
Bob Koch:Thanks for having me in to chat with you guys today. Again, I'm Bob Cook. I grew up in Minnesota, just north of the Twin Cities. Spent a lot of time working on my grandparents' dairy farm. Got my undergraduate degree in biology from St.
Bob Koch:John's University. From there, I did my graduate training at the University of Minnesota. And then I went and worked with the Minnesota Department of Agriculture for about six years focused on invasive species. And in 2013, I came into this position, research and extension focused on soybean insect pests.
Bill Hutchison:A large part of your program has been about soybean aphid to date. So I think that's going to be the main focus today, to get an update on this year's situation with soybean aphid, as well as your current research based recommendations on IPM for soybean aphids. So Dave, kick it off.
Dave Nicolai:Well, Bob, again, thanks for stopping by. And with regard to the soybean aphid management, you know, looks like right now we're in here to the July when we're recording this podcast, but I think we're right on time in terms of soybean aphids because certainly is a topic that's come up in terms of scouting reports, etc. And we noticed that yourself and other folks have been involved in some articles in our crop e news series out of the University of Minnesota Extension. So can you give us maybe some details about where some of the infestations and preliminary results are coming from in the state of Minnesota? Keep in mind obviously that things can change here.
Dave Nicolai:Give us a snapshot of where we are today.
Bob Koch:Yeah, sure Dave. So I think the main message right now is that it is definitely time for folks to be in their fields scouting for soybean aphids. You can find aphids pretty much in any field now throughout the state, from the southern part of the state to the northern part of the state. But we really want to be paying attention right now in Central Minnesota, where some of our scouting reports and contacts are indicating that soybean aphid populations are growing pretty quickly there. Some fields are being treated so they're near threshold levels.
Bob Koch:And that's areas like Stearns County, Meeker, Kandiyohi, Pope, and Douglas. Not just those counties but kind of that general area. And I think why we're seeing more aphids there is that part of the state missed out on some of the real heavy rains earlier on in the year. We know that real heavy rains with strong winds, especially when the plants are small, can take a toll on the aphid population. So I think that's kind of what helped knock those aphid populations down in Southwestern Minnesota and Northwestern Minnesota.
Bob Koch:Well, kind
Dave Nicolai:of explains the next question I was going to ask that we should preface this by indicating to the audience that it's July 18 today when we're recording this. But in regards to these variations from year to year, do you think a lot of that has to do with the weather systems that come through and so forth as far as where we pick up these aphid populations? Because I know some years we have them a little higher, say for example, in the Fergus Falls area, sometimes in the Northwestern Minnesota, but there is variability. In some years it's
Bob Koch:in Southeast. So is your feeling based on that primarily in weather system situation, but certainly there could be other factors too? Yeah, that's a pretty tough question, Dave. There's, you know, weather plays a big role from winter temperatures. These insects overwinter as eggs on buckthorn.
Bob Koch:So if we get, you know, extremely cold temperatures we could have some overwintering mortality, so fewer aphids. Going into the next year there's also the weather around planting time. If growers are delayed in getting their soybean planted because it's too wet maybe, then you might get kind of a gap between when aphids would be leaving Buckthorn trying to find soybean. So if soybean is going in late, there might not be soybean available for the aphids when they come off the Buckthorn. And if that's the case, populations might be lower that year.
Bob Koch:It's a complicated puzzle, Dave, and I don't have an answer for you.
Dave Nicolai:Well, we'll keep working on it, that's for sure, with research. But certainly, what I think a grower can do at this point in time in those areas or in other areas of Minnesota is to go through some of the steps in terms of integrated pest management, in terms of looking and visiting that field. So can you give us an outline here in terms of scouting recommendations, economic thresholds, etcetera?
Bob Koch:The main approach for managing soybean aphids right now is through use of insecticides. And we want to be applying those insecticides based on information about the pest. So we have to be getting into our fields and doing actual scouting. So looking at plants, estimating or counting aphids on those plants, and then coming up with kind of a field wide average for the number of aphids per plant. And then comparing that to the economic threshold, which is two fifty aphids per plant on the majority of the plants in the field.
Bob Koch:So more than 80% of the plants with aphids. And in addition to that, we like to see those aphid populations increasing. So two fifty aphids per plant, that's the trigger point for lining up the insecticide application to keep that aphid population from reaching damaging levels, which is the economic injury level. And that occurs at, you know, maybe 600, 700 aphids per plant.
Dave Nicolai:So the economic threshold level is designed to allow growers to make plans, etcetera, start situations, you know, prior to the economic injury level. I know that, you know, every year we get questions in extension and farmers and ag professionals do as well, that the price of soybeans does go up and down, and certainly that's the case this year, but yet we maintain that economic threshold in there. Why don't you talk a little bit about what the research is based on in terms of that, because it's dynamic, but it still allows you to target that a little bit irregardless of some of these price fluctuations. Yeah Dave, that's a
Bob Koch:good point. So the economic injury level is based on commodity values and input prices. Management recommendations for soybean aphid coming out of the University of Minnesota and the other universities in the region are still focusing on that two fifty AFib per plant threshold. Our research across multiple states, multiple years, still shows that that is an effective threshold for protecting soybean from economic yield loss. And understanding of the biology of the system also supports this threshold because we know that soybeans can tolerate a substantial number of aphids on the plants before you get any measurable yield loss.
Bob Koch:And that economic threshold is still below that value that would cause any even measurable yield loss, let alone economic yield loss. Good to hear that experience from other states as well supporting the economic threshold at $250
Bill Hutchison:per plant. I just wanted to go back briefly to ask a follow-up question about scouting to determine that threshold. You know, we've heard the term speed scouting mentioned a lot in the Midwest and in Minnesota. Can you tell us a little bit more about that or what you're currently thinking on scouting recommendations?
Bob Koch:There's two different approaches for scouting soybean aphids that we're recommending. The first is the one that I already explained, going into the field and counting or estimating aphids on plants and relating that to the two fifty aphid per plant threshold. The other approach is the one you mentioned, Bill, and it's called speed scouting. And this approach, for some people, it's more efficient, a little quicker as its name implies, speed scouting. What you do here is you go into the field and you're looking at plants again just like with the other scouting approach.
Bob Koch:But instead of estimating or counting the total number of aphids on those plants, you just look to see if those plants have more than 40 aphids or less than 40 aphids. If they have less than 40 aphids, you consider them uninfested. If they have more than 40 aphids, you consider them infested. And then we've got worksheets available or there's even an app from Nebraska where you can tally up the numbers of infested plants and uninfested plants and then make a treatment decision based on that.
Bill Hutchison:I've heard a lot of positive feedback about using that system throughout the state, so that's good to hear. I guess another obvious follow-up question. Grower crop consultant determines they're over that threshold and they do need to schedule an application. Where are we at with current insecticides that are available in Minnesota?
Bob Koch:Yeah, so for labeled insecticides for the soybean aphid, we've got a lot of products that are available to us. But if you step back and think about what insecticide groups all those different products come from, we're actually pretty limited where we've got only three insecticide groups available to us. Group one which has the carbamates and organophosphates, group three which is pyrethroids, and then we've got group four which is the neonicotinoids and some of the other chemicals that are similar to the neonicotinoids. Over the years we've been relying really heavily on the pyrethroids and organophosphates, especially chlorpyrifos. Having this heavy reliance on just those mainly two insecticide groups isn't an ideal situation in terms of insecticide resistance management and integrated pest management.
Bill Hutchison:So, right, that's always going to be a challenge. And I know you've been actively involved in documenting a few hotspots in the state or even in other states where resistance has cropped up, at least as of last September, last summer. Have there been any concerns with resistance yet this year? Is it too early to know? Were we at?
Bob Koch:Yes, the development of insecticide resistance in the soybean aphid has been a big issue over the last two or three years. So going back to 2015, we first documented it in Minnesota in the Southwestern part of the state, and then again in 2016 but from a wider geography. And then last year was the biggest resistance situation. Reports of failures of the pyrethroid insecticides and documented resistance based on laboratory assays for aphid populations from Southern Manitoba down into near Iowa and then from both the Dakotas and multiple locations within Minnesota. So we've got three years of data with resistance showing resistance of soybean aphids to the pyrethroid insecticides, things like bifenthrin and lambda cihalothrin failures from a very broad geography.
Bob Koch:So this is a serious issue that we're dealing with, especially considering the fact that I mentioned earlier that we've got so few insecticide groups available for management of this pest.
Dave Nicolai:You know, along with that, Bob, and we're going to talk a little bit more about Copiriphos here in just a minute, but were there some isolated instances of perhaps resistance in the Copiarifos area or is it situation where we have growers, you know, experimenting with trying to tank mix situations here, thinking they're going to get around resistance issues, mixed modes of action, so forth. Any quick comments about that?
Bob Koch:Dave, to date so far the only resistance that we've documented is to the pyrethroid insecticides. We have no evidence of soybean aphids being resistant to chlorpyrifos or the other organophosphates. However, if we start using more of those insecticides because the pyrethroids aren't working, that story could change in the future. Know there is the chance that our aphids could develop resistance to chlorpyrifos. There are reports of soybean aphids from Asia having resistance to some of the organophosphate insecticides.
Bob Koch:So they definitely can do it. The thing with products like chlorpyrifos is they've got shorter periods or durations of residual activity. So you can make an insecticide application with a product like that get very effective control, but the insecticide might wear off from the plants over a short period of time and you can get recolonization by the aphids and those aphid populations can rebound very rapidly. So that might explain some of the situations that you've heard. Or cases where folks are maybe dabbling around with tank mixes, maybe with too low of rates, or things like that could also contribute to issues like you're seeing.
Bill Hutchison:So a quick follow-up on the resistance topic going into the soybean aphid season this summer. I'm reminded this morning that you've actually got a nice team together that's helping monitor populations throughout the state. Bruce Potter, IPM specialist in Southwest Minnesota. Phil Glagoza, I believe has been involved. So if farmers or consultants after a spray, after an application, get some indication that maybe that application did not work well or they might suspect resistance, what are sort of the best steps, the next steps that they should take to contact somebody on your team?
Bob Koch:Yeah, I think the resistance issues for this year, they are a reality. We've got one population assayed from this year from near Wilmer where it was showing reduced susceptibility to the pyrethroid insecticides. So it seems like a problem that's not going away. If somebody makes an application with an insecticide and it doesn't do what you expected it to do, the first thing we want people to do is to try to rule out other causes. You know, was there applicator error, plug nozzles, you know, maybe using the wrong rates, you know, think about the environmental conditions.
Bob Koch:And then if you can rule out these other potential causes and you're still thinking it could be resistance, we definitely want to hear about it. So you can contact your local or regional extension educator, extension entomologist. And what we would like to do is to continue to kind of document how big this problem really is geographically. And we also like to send our staff out to these fields to collect some aphids and we can do laboratory tests on them to try to confirm if it was resistance or something else causing that problem.
Bill Hutchison:So the other thing, Bob, that I hope we can take a little bit of time to cover today is when we think about Integrated Pest Management, obviously we don't just want to rely on insecticides. And I know you've done some work with host plant resistance looking at some of the newer potentially resistant varieties as well as looking at conserving the beneficial insects as much as possible in soybean. Can you give us some updates on where these options are at?
Bob Koch:Yeah, that's a good point, Bill. So integrated pest management, the core of that idea is integrating multiple tactics for management of the pest. I mentioned that right now we're primarily relying on insecticides, but we do have highly effective aphid resistant varieties that are available. Unfortunately, they're not very widely available. We've scoured seed catalogs and found about a dozen varieties that would be adapted in terms of maturity groups for use in Minnesota.
Bob Koch:Our hope is that more and more of these varieties will become available, especially considering the insecticide resistance that we're dealing with. Having another management tactic would be a great addition to our management programs now. In terms of biological control, we've got good insects out there working in our favor like the lady beetles and other predators. So if you're thinking about using the insecticides for managing the pest, you know another reason to rely on that threshold at two fifty aphids per plant is that it gives these lady beetles and other predators a chance to work against the aphid population. And then if they can't suppress it, then come in with the insecticide to knock that population down to protect yields.
Bob Koch:And in addition to those predatory insects, we've got a tiny parasitic wasp that came over from Asia and these wasps make their living by injecting their eggs into the aphids. The wasp larvae then hatches out of the egg, feeds inside the aphid eventually killing it. And then the adult wasp will emerge from that aphid, kind of like the Aliens movie from back in the day. Colleagues from Michigan, some of the Eastern states, and Southern Canada have suggested that this wasp may be contributing pretty significantly to suppression of aphid populations in those states where they're not seeing the outbreaks that they used to anymore. George Heimpel's lab in Minnesota has documented this wasp throughout the state over the years.
Bob Koch:Numbers appear to be increasing so we've got our fingers crossed hoping that this thing will continue to increase and keep working in our favor to prevent or to suppress aphid outbreaks. Bob, you know, in terms of
Dave Nicolai:kind of wrapping this together, if you're farming in Central Minnesota or some of these other areas that we're talking about hotspots, in thinking about the biology of the aphid and the biology of other predator controls and other insects out there, how often should, if a farmer isn't speed scouting, visit that field in terms of doubling time of
Bob Koch:the aphid population and so forth? Any quick recommendations in terms of making visits you know, we're into the seventy, eighty degree temperature regime here going forward? So in general, we recommend that people are scouting their fields on a regular basis, maybe every seven to ten days. But you mentioned temperatures in the 70s and 80s. That's kind of the sweet spot for soybean aphids.
Bob Koch:Just like us, they don't like the extreme heat. Their reproduction slows down, their mortality increases. So if you have weather conditions like we're experiencing this week, aphid populations can grow very rapidly. They can double population sizes in a matter of just a couple of few days. So if you have a population that's nearing threshold and you're in these time period with these favorable temperatures for aphid populations, may want to be scouting even more frequently.
Dave Nicolai:We're recording this podcast prior to our major rain event here, there'll and be other major rain events. But any last words here, last question for you, and when you have those rain events, can they be significant in terms of perhaps control of the aphids, or can they survive through that and you just have to get right back out in the field and keep scouting?
Bob Koch:Dave, so these rainfall events, if we've got heavy rain and strong winds, we know it can knock aphid populations down, especially if the plants are small. But once those plants get bigger, the canopy closes over, those plants can provide pretty good protection for those aphid populations. So if you're scouting and maybe getting close to making a treatment decision and you have a big rainfall event coming up, you might want to scout again just to check if that rainfall event worked in your favor in knocking that aphid population down and if you really need to treat that field.
Bill Hutchison:Okay, Bob, just to wrap up today, I know our main focus today has been soybean aphids, still the key player in the state. But another emerging pest issue that's getting a lot of attention right now is Japanese beetle on numerous crops, vegetable, fruit, field crops. What are you seeing with Japanese beetle on soybean right now? What would you anticipate in terms of any initial damage projections for this year?
Bob Koch:Yeah, so Japanese beetle populations have been increasing over recent years quite rapidly in the Southeastern part of the state, especially around some of the larger urban areas. So agricultural areas surrounding the Twin Cities or surrounding some of the larger cities like Rochester and some other cities in the Southeast. And we've been seeing fields near treatable levels in these years. This insect, the Japanese beetle, it's the adults, they feed on the soybean leaves causing defoliation. Treatment recommendations or economic thresholds that we're recommending are 30% defoliation prior to flowering and 20% defoliation after flowering.
Bob Koch:Those measures of defoliation are for the entire soybean canopy, so not just a couple leaves here and there. You want to select plants scattered throughout the field and then look at leaves on the top, middle, and bottom of those plants and estimate the defoliation, average that within those plants, and then across those plants to get that overall canopy wide defoliation level for making that treatment decision.
Bill Hutchison:Okay, sounds good. Well, thanks again, Bob, for taking some time out of your schedule for this mid July update, and we hope to talk to you again soon.
