Corn Rootworm Resistance Management  - Okay, our next speaker in this segment probably doesn't need any introduction. I think most of you probably know Bryan. Bryan Jensen has a very short resume, by his request. Currently works for the UW-Extension and the Integrated Pest Management Program in the Department of Entomology. Please welcome, Bryan Jensen. (applause)  - I will only listen to my obituary one time in my life. I don't get it started too quick. OK, we're gonna talk about corn rootworm resistance management. First, let's get on the same page as to what resistance is in the field. In the past we had the luxury, if you wanna call it the luxury, of being able to collect several thousand beetles from problem fields, from local fields that did not have problems sending them into a university lab or US State lab for them to do a bioassay on those beetles to see if there's resistance. 

A very good method of determining if we have resistance, but that's more or less to document the early stages of resistance. We can't afford that anymore. We can't afford that luxury. You cannot afford to pay the full cost of that bioassay. So what we've determined is some guidelines to help you in the field to determine what resistance is. First, if you've been using a single corn rootworm protein for more than two years in a row, and you have an average root rating, an average nodal-injury scale root rating of greater than 1.0, you can assume there is resistance in that field at that time. Or, if you've been using a pyramid, meaning that you have two rootworm proteins and you have been using that trait, that set of traits for more than two years in a row, and you have an average root rating of .5 or greater, assume that is resistance.  One thing I cannot tell you and I don't have good information on is the number of acres that are affected in Wisconsin by corn rootworm Bt Resistance. You know, there's some confidentiality problems with that, and we just don't have a good handle on that, but to give you a bit of an idea on where we're sitting in Wisconsin. During the 2014 Pest Management Update Meetings, at each of those eight locations I asked people to raise their hand to help me determine whether or not they had been seeing any problem fields in their area. 

And at all eight locations, at least one person raised their hand. Certainly more in the southern part of the state, fewer in the northern part of the state, but I got at least one hand raised at each location.  And I also would like to thank members of WAPAC, the Wisconsin Association of Professional Ad Consultants, in helping me out with a survey during a busy time of the year for them. The survey was conducted in July of 2015, and first question I asked was their overall concerns about Bt Resistance in their consulting area. 92% of the people that responded were slightly, very, or extremely concerned, and eight percent of the respondents were not concerned. Then the next question I asked them for some feedback on the extent of rootworm resistance in their consulting area. What I was looking for was some validation, some professional validation, of whether not they had it, the resistance in their area. 33% had one or more fields that they had verified as having resistance. 16% said they probably have it, but have not been able to verify it. It might've been a word of mouth type of thing. 

33% said they did not confirm resistance, nor has a reliable source. And 16% weren't sure if they could tell the difference between resistance and maybe non-expression.  I also asked two other similar questions. First was on their concerns about the short term viability of the Bt hybrids. No one was not concerned, but for the short-term viability, 75% said they were slightly concerned, 25% were very or extremely concerned. When I asked that same group about the long-term viability, those numbers were flipped. 25% were only slightly concerned, and 75% were very or extremely concerned.  Okay, I'll throw this comment up, and I think we all probably will agree with it. Our goal is to maintain the durability of the Bt corn rootworm hybrids, right? Is there anyone gonna disagree with that? It's a good rootworm management tactic...  but we gotta face the facts, and the facts are we've been outmaneuvered by corn rootworms. 

 Again.  And the pessimist inside of me says something else will happen again with rootworms. Rootworms in a field crop area are our poster child for resistance. Not quite to the standpoint of where corn, or, ah, Colorado potato beetles are, but in the field crop areas, that is the insect, that set of insects, which have our greatest concern for resistance. They've become resistance to our, in some cases, to our rotation, and if you would've asked me in 1985 if that was possible, I might've tried to keep a straight face and said, "No, I don't think they'll ever do that." They have. And each species, the Northern and the Western, has their own way of overcoming our rotation. Back in the olden days before I started, they became resistant to some of our soil applied insecticides. Different classes than what we use now, but in the past they've been able to do that, and also a little bit more currently they've been able to become resistant to some of our foliar applied insecticides. I also think we have to face the fact that Formula Farming to manage rootworm does not work. If you do the same thing long enough, pretty soon, it will be wrong, and I think we're seeing that right now with rootworms. 

And also I think we're gonna have to learn, if not relearn, how to manage corn rootworms using an IPM approach.  What do we know right now? It can be a long list but I've boiled it down to four bullets. Currently only the Western corn rootworm is resistant, although there has been some suspicion that the Northern may have some resistance problems as well. Resistance has been confirmed to two of the four commercially available proteins, and a cross resistance has been confirmed to those same two proteins.  And likely resistance to Bt hybrids is a dominant trait, and I don't think we're gonna be able to wait this one out. We're not gonna be able to turn the clock back. If we don't do something to change our rootworm management practices, we're gonna have to live with that decision for a long time. So Wisconsin, as compared to some of our neighboring states, Illinois, Iowa, and especially Minnesota, they're much further along that path to resistance than what we are. I think in Wisconsin, we have the chance right now, to make a lasting, long-term impact on how we manage rootworms, and in certain areas of those three states that I named, the Bt hybrids are not working very well, and they've had to go through to use some other management tactics to keep ahead of those insects. In Wisconsin, I think we're at that early stage. 

I think we can make some decisions now that are gonna impact how we manage rootworms in the future. Some favorable impacts for the future. So we're gonna have to use and IPM approach and that starts with field monitoring, and what I'm talking about with field monitoring is beetle scouting and root evaluation. It will be more intensive. And there have been times I've been criticized, maybe that's too strong of a word, but I've been taken to task and people tell me people are just not gonna do it. Okay? In that WAPAC survey I asked a question, "are they scouting for beetles?" Only six percent do not scout for them now, and do not intend to do so in the future. 65% scout for beetles now, and do not intend to increase that number in the future. 14% do not scout now but intend to start in the future. And 14 currently, 14% currently scout now, but intend to increase beetle scouting in the future. If we don't scout for beetles, if we don't evaluate our roots for rootworm damage, we are losing a really important piece of information to manage corn rootworms in the future. 

If we don't have that baseline information, how do we diverse fire management tactics? By guess? If you've got the beetle scouting information, you can feel much more comfortable in making those controlled recommendations. And I would guess your comfort level in making those recommendations is pretty important to you.  Ah same graphics that Krista threw up, and I'm glad she did.  The graph on the left you've seen already. My point there, I think, kinda helps solidify the need to scout for beetles. Sure, there's a lot of orange dots in there, and I know you can't read the key at the bottom, but those are the fields that are over threshold right now that they scouted for in 2015. But there's a lot of black dots, green dots, yellow dots. Those are fields that are below the economic threshold. And Krista also talked about the graphic on the right. There has been some increases in areas of the state, but generally, look at those numbers. 

They are still pretty low.  Okay, so, as I mentioned before, we can use that field data to diversify our management practices. Basically what we need to do is to count beetles when they're out laying eggs. Beetles are out flying for a very long period of time, but we need to scout during that early August through early September stage when they're laying the eggs. The economic threshold is an old one, .75 beetles per plant. That was developed when plant populations were lower than what we have today. So ratcheting down that threshold a little bit I think makes sense, especially if you're going with higher plant populations. Also, the old recommendations were to visit the field one time, if you were over threshold you could quit scouting, you know you need to treat, rotate out of that corn the next year. But now in this day and age when we're looking at managing resistance, and to diversify our tactics a little bit, it does not hurt to make at least one more visit to that field. Certainly we want to identify if that field is over threshold, but what we also wanna know is that the peak of the rootworm populations in that field, or are numbers going down or going up? If they're going up, that would be an important piece of information to have, because populations do change over time, they're mobile, and can change from week to week. 

Root evaluations, the value of that data, determine the efficacy of your rootworm practice. You spray for weeds, you go back and re-scout those, right? Just to see if whatever you used is working or if there's been more emergence after that, doing the same thing with rootworms is a good practice. Think, part of that is that it will give you more confidence in the use of the soil insecticides. I think we've gotten to the feeling that the Bt hybrids are by far and away our best management tactic. They are a management tactic, but prior to the release of the below-ground traits, well how did we manage rootworms, in part, to a great degree on continuous corn? We used soil insecticides, and we did use them effectively.  It can also track your potential for resistance over time. I don't think you're gonna go from a susceptible population to a resistant population in a one year period of time. You, by checking your roots on your Bt hybrids, you'll get an early warning of when resistance is building up. And then on first year corn it can confirm the presence or absence of the rotation resistant or Eastern variant of the Western corn rootworm. That will tell you what happened last year. 

It will not maybe project what, it will not project what will happen in the future, but it will give you more confidence in not treating first year corn, perhaps. Then finally, just to finish up, I would like to review some of the rootworm management practices. Kinda look at where their niche might be, some of the pros and cons.  First, the Seed Treatments. And what I'm talking about are the rootworm rates, the high rates of Cruiser and Poncho. They have a niche, and I think when you go back to that map that Krista showed, there's a lot of fields in the state of Wisconsin where the Seed Treatments have value in it. Those low to moderate populations. So that can be one of your management practices for those fields with low to moderate populations.  Also the use of the Soil Applied/At Plant Insecticides on Conventional Hybrids. You know, we were talking about the liquids, the granules? Choose your product wisely. 

Some are certainly better than others.  That is what we used prior to the Bt hybrids, and quite frankly, we did a pretty good job of managing rootworms at the time, but you gotta calibrate. If you walk behind that planter and each box is set at the same number, you know that planter was not calibrated.  And also rotate your modes of action. Right now we have the pyrethroids, and we have organophosphates. Do try to rotate those modes of action to present, to slow down any resistance. And with that I will say right now we do not know within Wisconsin or the Midwest of any issues with resistance to those classes of insecticides. The downfall, right now not all planters are plumbed or boxed for the soil insecticides. That might be an option you can have growers look at. Their niche might be fields with a moderate to high populations... 

 and/or fields with a history of secondary insects. The Insecticides applied at Calibration, boy that's a niche, is a last resort. If, by chance, someone messed up somewhere along the line, did not put any protection down, whether it was a Bt hybrid when there should've been, these insecticides applied at cultivation can offer you, might offer you some control. You'll need the correct application equipment. Timing will be important. You'll need adequate rainfall and/or irrigation to move that insecticide down into the soil profile. Some products are labeled for that. You'll see some lists on there, it's not an exhaustive search, others may be available, but again I think the take home point there is this is a last resort if something didn't, if something didn't work, you had a mess up with recommendations and the Bt hybrid was not planted or you ran out of insecticide, something like that. The Bt rootworm Hybrids. I think their niche certainly is with the fields with high beetle pressure, with the assumption that you do not have resistance started in that field already. 

Check those roots. Make sure you don't have that resistance started. And as Krista mentioned, I'll say the same thing, rotate those proteins every two years. Annual rotation is even better.  Often get the question, "which is better, pyramid or single proteins?" and being from Extension, I gotta say that depends. You know, it's not an easy yes or no question. It is beneficial if both of those proteins work, and have been working. However, if control is questionable for one of those proteins, and you use that pyramid, you will continue to select for resistance with that compromised protein. The viable protein may, for a short period of time, provide control and mask any resistance problems. And the big take home message with that is if that one protein is not working very well, you are putting a lot of selection pressure on that other protein. 

So it's not a yes or no question, it's a maybe. If you know you don't have any resistance issues in that field, pyramids are a good resistance management tool. And then some people have been using the soil applied at plant insecticides with a Bt hybrid. We don't consider that a management tool, a resistance management tool I should say, because yes, you're using two modes of action, but that insecticide, that mode of action, is concentrated in the local root zone at the base of the stalk. You are not controlling rootworms on those lateral roots that stretch out a few feet. So for those roots and for those rootworms feeding on those roots, you have a single mode of action in that situation.  They do have a niche. Those fields with extremely high rootworm populations where all of our control tactics can be overwhelmed by putting an insecticide down with a Bt hybrid under known high population, that would be a good niche. What's one management tactic I have not covered? Anybody? - Tillage. - Tillage? Ah, not too much. 

They've adapted and have worked through both moldboard plowing, no till, and what we call conventional till chisel plowing, so not a lot of management there.  - [audience]: Rotation. - Rotation.  That is still a viable management tool. There are some problems with that, the producer...  may not want to rotate that field. You know, talk to 'em, and if you can't, you can't. There is also the rotation resistance rootworms that Joe was asking a question about a little bit earlier. Some problems there are in with the Westerns laying in soybeans, that's South, Southeast Wisconsin. And then the Extended Diapause in the Northern, not known to happen in Wisconsin at this point in time, but across the border in Minnesota there have been some cases. 

 And with that, you know, we can scout for beetles in soybeans, for the Westerns, using yellow sticky traps, kinda labor intensive. If you have a concern, that would be one way to, to be able to predict the potential for damage next year, but also just monitoring the roots on first year corn and conventional hybrids. It can help you feel a little bit more comfortable in treating or not treating first year corn.  The last one I'll talk about is trying to suppress adult corn rootworms with foliar insecticides. Its niche, and this is not really to topic very well, but certainly it is a good tactic for those early or late planted fields where you're concerned about Silk Clipping. That's not really a resistance management issue, but certainly it works there. As a stand-alone larval management tactic, I, as a consultant, I would feel really uncomfortable relying on adult suppression as my only rootworm management tactic.  You can easily misinterpret populations if you don't do things right. Nebraska and some other states have used it for a number of years, but to my knowledge, there's not a lot of it being used right now. In terms of managing population density, keeping the adults, it's got some potential there. 

The timing of application is gonna be critical. And what's, you know, rootworms are laying eggs for a three week period of time. Maybe a little bit more that that, but the concentration is that early August through early September. That's a rather long period of time. One spray may not be enough to really knock down adult populations that much, and the use, the long-term use of Bt hybrids has made this problem worse because rootworms. That has extended their life cycle a little bit. So they're gonna be emerging, the adults will be emerging just a little bit later, and you may get a significant egg laying pass the first part of September. It's also helpful if you can identify the gender of both the Westerns and Northerns. It's pretty easy to do with the Westerns, not so easy to do with the Northerns. You need a magnifying glass to do that, and also it helps to determine if the females are gravid. 

You can do the pinch test, you can look for extended abdomens, things like that, but also if there's a lot of pollen out there or silks, their abdomen, the female's abdomen will also be extended quite a bit. And also, you know, in the back of your mind, you gotta keep aware of the fact that rootworms have become resistant to some of the foliar insecticides that we have available today.  (applause) - Thanks, Bryan.