Managing Corn Disease in Wisconsin  - Up next we have Damon Smith. Damon is an assistant professor and Extension plant pathologist at UW-Madison. Damon's responsibilities include research efforts that focus on improving our understanding of the epidemiology of plant pathogens, in order to develop better management recommendations for the sustainable management of field and forage crop diseases. (exhaling) That's pretty intense. All right, Damon is a native of western New York state. He earned his Bachelor's degree in biological sciences at the State University of New York college at Geneseo. How'd I do? - [Damon] Nice. - All right, and his Masters and PhDs degrees from North Carolina State University. Prior to Damon's appointment at UW, he was an assistant professor at Oklahoma State. - All right. 

 Yes, that's intense, and I'm a pretty intense guy. You guys probably know that already, so. I guess I gotta do this close, because you can't hear me. It's the end of the day, right? I know I'm standing between you and the beer, afterwards here. So, I'm going to try to keep this moving along for ya, and, we'll jump right in to talking about some diseases. I think y'all will agree, the last couple of years, the two big ones in corn for us, here in the state, are Northern Corn Leaf Blight and Goss's Wilt. I know there's some other minor diseases, we talk about eyespot and some of these other things that move in, but I think if we had to classify and pick out the top players here, these are the ones that we're looking at. So, I want to take some time, my, from what I've learned over the past couple of seasons, I think, we've got a lot of issue in terms of just trying to tell the difference between these two diseases. I just want to take some time just to kind of tease this out, and then we'll look actually at some fungicide data over the last couple of years here in the state. So, Goss's Wilt, as Ned Phipps talked about earlier, this is sort of a reemerging issue for us here, especially in Wisconsin. 

It was discovered here 25 or 30 years ago. So, it's not an unusual thing to find here, but we sorta, were able to manage it. And I'll talk about why maybe we're seeing some resurgence here. It is caused by a bacterium. So Clavibacter michiganensis, subspecies Nebraskensis, that's a lot of words in Latin there, and if you're like me, I hate Latin. So we'll just call it the Goss's Wilt pathogen, 'kay. So, it is often confused with Northern Corn Leaf Blight because we get these really long, sort of broad lesions across the leaf, 'kay? And so, you can see some of this here in this upper slide, again in the lower slide there. It can have two phases, there's the wilt phase, and the leaf blight phase. I think you'll agree with me, that, what do we see most? The leaf blight phase, and that's really what confuses a lot of us, and it is found throughout the Midwest here. Some, common phases here, or things that we see in the leaf blight phase we see, we see these freckles. 

So how many are familiar with the freckles? Some of you have seen these. Some of you are awake and listening to me, so that's good. So, when you don't see the, when you don't have these held up to the back light, these freckles look dark. Scattered throughout this, bleached lesion. And then if you hold these up to the light, and get some back light behind them, they will often, change to being translucent in color. This is really, tell-tale sign here. We put a lot of merit, actually, when we're trying to diagnose this in the field, on these freckles. The other thing you can do is grab a piece of these leaves here, and you can actually incubate these in a, in a plastic Ziploc bag with a wet paper towel, and sometimes, if you're lucky, you'll get the bacterium actually oozing out of the leaves. So that's a trick. That doesn't always happen, but that is something that sort of helps you get, to where you need to be. 

The other thing is, is that, the lesions typically will be much longer than a Northern Corn Leaf Blight lesion. You know, the longest Northern Corn Leaf Blight lesions we typically see are maybe about six inches. Now what the caveat there is those lesions can coalesce. And you'll get a larger lesion from the conglomeration of those, but no single lesion will get as large as we see with Goss's Wilt in a lot of cases. The other, thing to kind of step back and look at, is the pattern in the field that you see these things occur, because that's really important when you're trying to tell the difference between Goss's and Northern Corn Leaf Blight. A lot of times, with Goss's, we're seeing the symptom actually starting on the upper portion of the plant. Why is that happening? Well, this is a bacterium that's actually getting inside the plant, it's disrupting the water conducting elements in the plant. And so, the farthest zones from the root system, obviously are the upper leaves, right? And so those are the first things that get starved by water, and so a lot of times, we start to see those symptoms appear at the top. Where's Northern Corn Leaf Blight typically start? Those of you who scout? Down lower in the canopy, right? So northern corn, we typically see it start low, and then it sort of progresses up to the top of the plant. There are sometimes exceptions to that rule, but generally speaking, that's what we see a lot of times. 

So the red zone here on this map, this sort of gives us the historical, what we might call the high risk zone. So, you've probably all seen data to Nebraska. That's sort of a hot zone, and of course, there's a lot of irrigated corn there. And so, there's a lot of work being done in that area of the country on Goss's Wilt. So we sort of extrapolate some of the management from those areas out to the other areas. Now in about 2010, 2011, we started to see, again, a reemergence of this issue here in the Midwest, and so, you'll see this sort of orange blob here on the map starting to stretch out, and that's the resurgence zone. This isn't to say that this is new here. Again, we found it 25 or 30 years ago, but it's sort of reemerged for us. Now we can drill down a little closer and that'll show some data from the state lab, which sorta lines up pretty closely with this map. We probably need to combine, data here. 

So this is from our diagnostic lab at UW, here. We've looked at data, I asked Brian to sort of compile, data, Brian Hudelson, in our diagnostic lab over the last couple of years. So before 2010, we had no confirmations, of Goss's Wilt. So 2010, we started to look for it, and you see, we did find, down here in Grant county. And you'll notice down here, Grant, Lafayette, year after year after year, this is kind of where we, first start to observe Goss's, each year. And you'll see in 2015, again, we had Goss's down here and then we had Colombia. I hear anecdotal evidence, over the last couple of years that Marathon, Lincoln, this part of the states had Goss's. This is generally not a zone where we find it. Again, a lot of this is related to the conditions. So higher risk things, things that we did this. 

Warmer temperatures, lots of rain, and then often some damaging event that, that like a hail event, which allows this bacterium to actually enter. So bacteria can't just enter the plant cells like, Northern Corn Leaf Blight can. It has to actually have some wound or other natural opening to get into the plant. So the patterns we often see, usually around where we see wind damage, hail damage and those sorts of things. So why have we seen this rise? I borrowed this slide from Marty Childers over at, Michigan State. I think this really kind of sums things up in a nice bulletin list. We've had a sort of change in production systems over the last few years. Corn prices were strong. So what did we do? We put a lot of corn on corn. This is a residue born pathogen, survives in that old corn residue. 

It also can survive on weeds in the field. So poor weed management can contribute to this, but we think a lot of the residual inoculum is in, in some of this residual corn residue out there. So related to that, minimal till systems, we've had a switch, which I think is a good thing for soil management, but this also is sort of a balance for us now, as we try manage these residue born diseases, right? We've moved to a minimum till or no-till system and that leaves a lot of residue around. So opening up the rotations here, can help us balance that no-till system and balance that residue that's out there. Also, the susceptibility in the hybrids certain genetics out here have allowed us maybe, to, we had a good handle on it, and then maybe we lost some of that resistance on hybrids, selecting for other things, like Northern Corn Leaf Blight, and so that may have driven, some of this as well. And then, we'll also have researchers in our pathology group also looking at virulence of these pathogens. So they're collecting isolates of this bacteria and investigating that. And it's likely that we have some increased virulence here in the Midwest which is contributing to that. So with that said, because we're dealing with a bacteria, we can't spray a fungicide. Darren talked about that in the previous talk. 

So we have to look at other things, that we can do besides just spraying something. And so, here's sort of the management plan in general. Plant the most resistant hybrid you can find, which is appropriate for your zone. Use some tillage maybe, if you're going to shorten the rotations. You know, if we're relying on a corn on corn type rotation, then we probably need to do something to manage some of that residue. So maybe, switching from no-till to maybe a minimal till. Doing something to try to get that residue breakdown. Again, longer rotations, obviously would be advised. I think with the price of corn, where we're at now, that might help our decision making process to get ourselves out of this corn on corn thing. And then good weed management, is recommended. 

So our, our colleague, Darren and my colleague at Purdue, they, just published a nice fact sheet, actually, looking at other grassy weed alternative hosts. So if you search alternative hosts to Goss's Wilt on Google, you'll actually come up with this fact sheet, and I'd encourage you to kind of take a look at that. You know one of the ones that are in there, Foxtail, things like that, these, they can be alternative hosts and contribute to the inoculum loads. And again, remember that fungicides, are ineffective here. We've also had some work done, both in Nebraska and Indiana, looking at baceteriacides and these sorts of other products out there besides fungicides. And they've been unable to actually find any efficacy, towards, this bacterium. So bare that in mind, there's not a lot that we can do in season. We've got to make some preparation in order to manage this. To sort of switch gears here, and talk about the other really important disease, we have Northern Corn Leaf Blight. Again, this is this has been a continuing issue. 

year in and year out, we might have a little bit of it. Other years more. The last couple of years, I'd say we've had quite a bit of Northern Corn Leaf Blight. And that's probably been our major issue that we've taken a lot of time to control. The major risk factors for Northern Corn Leaf Blight include a cool wet environment, so 2015 was the banner year, really, for the weather conditions that really favor this. We had a nice, cool season all the way along. and then we had heavy dews and rains that were pretty frequent, and that really favored not only the initial infections, but it also helps these spores move from the lower leaves up to the upper portions of the plant. There was also large amounts of residue in our, our corn on corn, and, and no-till systems, which are probably contributing. Again, we've got a residue born pathogen. Maybe some susceptible hybrids out there, again, a lack of rotation, and races are an issue here with Northern Corn Leaf Blight. 

So the most prevalent race, since about 1999, has actually been race 1. Race 0, was, is found in the Midwest, and that was one of the more predominant races in the 90s, and then we had a shift to this race 1. And more recently, we, were, there's some evidence that suggests yet another shift. So that could be also contributing to some of what we're seeing in terms of maybe an uptick in Northern Corn Leaf Blight. Just to show you some symptoms up close here, so this the sort of tell-tale symptom, again is that sort of cigar shaped lesion. Again, these things don't get much bigger than maybe six, seven inches long, but they can coalesce if you get enough of them on a leaf. And you can see, there's a couple of these lesions starting to coalesce here. So that's where people start to get confused. Now one nice, thing that does happen with Northern Corn Leaf Blight, is it is, it's a prolific sporulator. Especially when we have heavy dew. 

If you get out there in the morning, you're doing some scouting, a lot of times, you'll see this grey, growth on the, in the middle of these lesions, and that's actually the sporulation. If you had your handy microscope out in the field and could look at this, this is what you'd see, you'd see a lot of little hairs here, and then these little banana shaped spores, actually, on the ends of these hairs. So each of these lesions can give rise to thousands of spores. Then you can have hundreds of lesions on a plant, containing thousands of spores. You've quickly got millions and millions and millions of these things, just moving around. And this is one reason why, if the conditions are really conducive, you can have it move pretty quick. You can see I've just, I hear people talk about, "Well, it just blazed through my corn in a week." And that, that can happen if the conditions are right, just because of the number of spores you see here. In terms of management, choosing a resistant hybrid, you're gonna hear a pathologist go to resistance first. We still think that's a great tool and probably the foundation of any good, any great, management plan. You're gonna need more than the old Ht1 resistance, it's not going to be effective against race 1. 

You're gonna have to look at things with the HtN or Htm1, Htm2, et cetera. So, those things will, pick up the resistance of some of the other races that, may be predominating, the populations. Again, managing corn residue, I think where the prices of corn are at, that's going to help us, again, try to get ourselves out of this continuous corn rotation. Open the rotations up here, which will help us with the residue management. I'm gonna kind of jump to the punch line for the rest of the talk, here right off the bat. I gave my students a little lecture about foreshadowing in literature, and you can kind of give the punch line away early, and then show the data here. So really, we know from a lot of work, which I'm going to show you here in a minute, the best chance for economic return, in the upper Midwest here, is usually if a fungicide's applied around BTR1. Again, because we're starting to see diseases start at that time, and then we're trying to preserve yield on those ear leaves, and so, if, if there's active disease happening, prior to tasseling we, we would likely see some success with a fungicide application. If there's not really much happening prior to that tasseling period, then the success goes down quite a bit. So that's a really critical timing for us. 

So the goal here is, again, is to protect those ear leaves, and that VT timing is really the place that you want to be out there, doing some scouting. So what about using a fungicides on field corn? There's a lot of debate out there on whether we should just be recommending spraying fungicides across corn and soybeans and just take the yield benefits that we get. Again, like Darren alluded, I don't think it's that simple. I think you really do need to consider a few things here. We've got some pretty good evidence now, this table here is actually compiled by Kiersten Wise, however, myself, Darren and a lot of the pathologists in the corn belt in the US, (throat clearing) we all contribute data to this every year. And Kiersten updated this table for us, so what you're looking at here is the different years where we had studies, and these are. We're getting up into the thousands of studies now across this six year period. So there's a lot of observations in here that give us these meanings. And what you're looking at, is just looking at timing. Regardless of the amount of disease out there, what's the benefit over not treating across the corn belt at these various timings? So, if you want to just jump here to the six year average, you can kind of see there's some ups and downs across here, depending on the weather, and the response in the corn hybrids and that sort of thing. 

You can see, on average, about two bushels at the earlier timings of application, that standard timing at the V2 to R2, stage, giving us almost five bushels. And then the double application if went early and then came back later with a two-pass program, actually not giving us much added benefit, over the single-pass. And this is so, this is one of the reasons why we're really sort of focusing in here. Again, on the VT, because we see if we're just going to spray, regardless of the disease levels, the odds and the, and the added bushels are probably a little higher at that stage, versus maybe the two-pass, or the v5 to v8. I would argue in your decision making process, the other thing that you probably really need to consider, and I'm sure all of you do, as good, farm managers, is you gotta look at the pricing. And I've showed these slides before, and prior to, last year, we were really talking about things that listed, had a list price up here around $18 to maybe $24. And I know my industry colleagues beat me up all the time, that my pricing's too high, but these are the list prices that, that we can get ahold of. Now, what's going to change the game, probably, here a little bit, is generic formulations and we do have a lot of pre-mixed formulations. Darren talked about the combination DMI, strobular in products now. We do have some of those that are off patent that are coming off generic formulations for 2016. 

And so, now, we're looking at pricing, so I hear on the street. I hear that the pricing's going to be more $10-14. So maybe you guys can agree that we're down in this zone. So our current prices today may be $3 to $4 a bushel, $4 maybe strong. What we're looking at here, is in order to just cover our price of fungicide, I'm not figuring the application costs in here, now. This is just the product, we need somewhere between two and a half and almost five bushels to cover the costs with these generics. Now, if you look back, if we, we went back just a second and looked at the slide, we're right in that zone here with our VT. So we're just breaking even, if we look at the six year average across the corn belt. So before this, before we had the generics and the lower pricing, we were really struggling to try to get our money back on these applications. Now, we can just look at yield. 

And there's no denying that spraying a fungicide, generally on corn, gives us some positive return. When we just look at straight up yields. And we can see this, this is a trial in 2015, up at Arlington, and what I did here, is I just looked at the various timings, and I've overlaid the number of observations we had at those timings, here, out of that trial. Then I just looked at straight advantage over not treating, and you can see we had in the earlier applications here, we had maybe around five bushels, the VT, three and a half to four, somewhere in there, and then I've overlaid the break evens here. So the yellow areas here is where we would be with the generic formulation, so yes, we broke even in both the early and the standard timing. Usually, it's pretty hard to see things happening down here at the two-pass, we're sort of moving away from that. We think we really need to just get things down to a one-pass, because it's going to be hard to make up twice, that bushel that I showed you in the, break even in order to pay for the products. So really, the focus is up here. And so you can see, yeah, we probably broke even this year. We may have made a little money, as well, on some of those treatments. 

If we wanted to look at some other data, get out of Wisconsin, maybe look at Iowa. This is some data that Allison Robertson shared for me, or, shared with me from Iowa. So here's some trials here. Looking just again at timing, and what you're looking at is the frequency distribution of success compared to the non-treated. So, I obviously, bars going down, would be a loss in terms of yield, compared to the non-treated. And then a positive bar would be a gain. And so in the V5 timings in Iowa, you see there's a 50/50 chance, at least in the 2015 data of having, some success there at the V5 timing. When you look at R1, however, the success goes up quite a bit. And again, this is whywe lean toward this timing as being one of the important ones. And again, you'll see the mean advantage here, over the non-treated is around five, almost six bushels. 

Five and a half to six bushels in the Iowa data. But again, you can see the, the two-pass program, yes, it gives us a little bit higher mean yield, but really not, I wouldn't argue a significant advantage and so, again, even in the Iowa data, since this VT-R1 timing seems to again be the one that we lean towards. Now, I would argue like Darren did in his talk, the disease levels really do matter. And I know, that that means we've gotta get out and we've gotta do some work to make that decision, and it's just not as simple as saying we're just gonna spray all the corn and soybeans out there. I wish it were that simple, but it's not, and we really have to consider disease here. In 2011, there was a nice research publication, that came out. Actually, some data from Wisconsin when Paul Easker was here, was included in that, and so I just want show you some, some things out of that trial at that time, or out of that set of data at that time. It looked at some different products and at that time, there was still some single mode of action products being applied on corn, so they looked at Headline, and they also looked at some of the pre-mixed products now, which are more common, the propiconazole plus trifloxystrobin combination, and the propiconazole plus azoxystrobin combination. Now, if we want to just look at straight up yield, compared to the check here, so we've got these box plots which show the mean and then the variants around that mean. Yes, we, we definitely get some sort of mean yield advantage over the non-treated, when we look at these various products, and especially with some of the pre-mixed modes of action here. 

There's no denying it, I think any pathologist will tell you, "yes, that does happen." Now, what, what you really need to consider though, is how much advantage are you getting and is that really going to actually cover your costs? Because a lot of times, people get tunnel vision and they just think, well, boy I got positive yield. And, and I must be getting some advantage here. But you gotta still pay yourself. You gotta pay for the application, you gotta pay for the product. And so they took that into consideration, and they split out the chances of getting your money back, based on the amount of disease that was there. Okay. So what you're looking at, and I've highlighted this group of, of tables here, and this group of tables, because these are the pre-mixed products. So these are the things that you're most likely to be spraying these days, and what you're looking at here, is the probability of not offsetting your fungicide costs. So, of not having success.  So in the, graphs here on the left, a higher line would actually say there was less success in having and recovering your fungicide costs. 

Versus a lower line, which would tell you that you had higher success. And so you can see, where, if all your disease severity was less than 5%, the odds of actually getting your money back were pretty low, at the various corn prices. So these lines are just the various corn prices. Now if you look at when disease severity was higher than 5%, so when, when in this case, it was grey leaf spot on the ear leaves was higher than 5%, that success goes up quite a bit. And the odds of getting that back, now, at some of these corn prices, are actually pretty good. If you could just hold the question until we get to the end, because we're, we're recording here. So, now let's look at what's going on in Wisconsin. So I can do the same analysis. This is called a meta-analysis. I can actually go back in time, we can extrapolate that data. We can do another, set of analysis on the variants and means, and I can calculate some probabilities for here in Wisconsin. 

So that's what we did. I just did this a couple of weeks ago. We went back in our data sets the last three years, from 2013 through 2015, and then we used observations only from the pre-mixed fungicides products. So, only where we had DMIs plus the strobilurins. Again, I think these are the things most relevant to the corn industry right now. And then we looked at timing, V6, V8, or VT. We had a total of 41 replicated study observations within this data set, so it's a pretty good data set in that study. And then we looked at distributions and meanial advantage, and all these sorts of tasty tidbits here. So we can line up the frequency distribution, just like we've done with, in previous studies here. And so what you're looking at are the yield differences relative to the non-treated check here, out of those 41 studies where we had, those pre-mixed products. 

And it's interesting when you just line them up, not taking into account the disease levels now. So just straight up yields, no disease levels in this analysis here. You can see that the distribution of positive return versus negative is actually pretty equal. And actually it's right around 51% at positive return. Now, if you're into statistics, I'm into statistics, so I like to look at these things. So, my confidence, actually, in getting this positive return is actually fairly low, because the statistics tell us that the probability of chance actually comes into be a big player in this data set, mainly because the frequency distribution is pretty equal. So basically, what it's saying is we have equal odds. We have a coin flip, regardless of whether there's disease out there or not, of getting those 2. 2 bushel mean advantage.  Not great odds. I don't know if I want to leave things up to a coin flip. 

I'm not that, that bold. Now what I can do, I can go in and parse the data set out, and account for the disease levels. So, I, again, this is Northern Corn Leaf Blight, now, because that's our main issue here. And we used the 5%, disease severity threshold. So very similar to what was, what was done in the prior study. Now in the top graph here, you're, you're looking at the frequency distribution of studies. Now we've cut that study, kinda down, to fewer observations here. And, 'cause we've had to split out the high versus low disease. But you see, when disease levels are less than 5%, we have very little likelihood of actually getting positive return. In fact, the mean, if you just want to look at the straight up mean, is actually a negative mean. 

Now that's really not different from zero, if you want to talk statistics, it's not significant. However that's not very, positive in my mind, when we don't have a lot of disease around, especially Northern Corn Leaf Blight for us here in Wisconsin. Now, we can look at it from the other direction, if we had high levels of Northern Corn Leaf Blight, maybe greater than 5%, now we're talking. 74% percent of those observations were positive, the mean yield advantage here was 5. 4 bushels, and we had a highly significant mean. And this is, this goes with what was published earlier in that other data set, they were looking at grey leaf spot, we're looking at Northern Corn Leaf Blight, but we're seeing very very similar responses. Now the other nice thing that we can do with a data set like this, and, the calculations that we can do, sort of in the background, with with statistics, is that we can then come up with some probabilities in return, similar to what they did in 2011. So I did that, I took those means from the high disease situation, low disease situation, I used our generic products, sort of where we're gonna maybe calculate some return on investment, and then I was actually able to generate the probability of recovering the fungicide application cost here. So you're looking at the probability that we will get some return in this particular chart for the low foliar disease pressure. So, if our corn is somewhere between $3 and $4 a bushel, that's what we can sell it for, we're looking at this green, or this light red line here, and if we're considering the generic products, our range of success here.  Whoa, that's interesting. 

Our range of success here is somewhere between 12% and 22%. In the low disease situation. So you'll remember from the frequency distribution, we did have a positive mean, but it was only 2. 2 bushels, and that's not enough to pay yourself back. You're going to lose money, even though you've got a positive return. Now in the high foliar disease pressure situation, the game completely changes. You'll see that these lines go up quite a bit. So if we look in the same scenario here, using those means, and they, and the corn costs $3 to $4 dollars a bushel, now we're up at 50% to 65% probability of success when we use a fungicide.  Disease matters, okay. And, and the level of return that you're gonna get matters. Not just being a positive return in terms of yield. 

So the summary here, foliar diseases can rob yield on corn, there's no denying that. Fungicide application in fields where foliar disease pressure is high, equals a high odds of recovering the fungicide costs. Sure. I will be with you every time, go out, spray, control the disease. That's what fungicides are for. Fungicide application in fields where foliar disease pressure is low, there's low odds of getting recovery. Sure, you might be in a field where you put a check strip in that field and you might have 30 bushels in that hot area. You might go to the next zone in that field, where maybe the soil type's not as good and you might be 30 bushels the other way. I get that question a lot. I put one strip in my field and I had 30 bushels advantage. 

My argument there is, go put another strip in another part of the field and see what advantage you've got. You've got to replicate these things across the trials. Okay, and take that mean advantage. And fungicide application timing, if you had to ask me, what the critical timing would be in Wisconsin, I agree with my colleagues in the other states. I think the VT/R1 timing is where success is gonna be. So you need to do some scouting prior to that timing to make your decision. If you've got active disease on the lower leaves, especially Northern Corn Leaf Blight, get out there and do some application. If you don't, follow it through the silking period, and if you still don't see things showing up, then you can probably, hold off on that fungicide spray. So I just kind of rattled through some of these recommendations here, again, do some rotation. Residue management. 

You've gotta do some scouting. The best time to apply would be that VT/R1 timing. (applause)