Field Crop Webinar Series - Tar Spot in Corn & Other Emerging Diseases

March 25, 2019

MSU Extension field crop pathologist Dr. Martin Chilvers addresses tar spot in corn - a new crop disease in Michigan in the past few years.  Tar spot of corn is a new disease to the United States. Caused by the fungus Phyllachora maydis, the disease has the potential to cause significant yield loss. Tar spot was first found in Indiana and Illinois in 2015 and confirmed in Michigan in 2016. In 2018, tar spot was observed in 27 counties across Michigan and caused losses of more than 50 bushels per acre in some fields. A new extension resource was published recently on the Crop Protection Network—look for “CPN-2012 Corn – Tar Spot” under the library tab.

Video Transcript

- So, Good Evening Everyone! - Yeah! - My name is Martin Chilvers, Field Crop Pathologist at Michigan State University. So, tonight we're really gonna focus on tar spot of corn, but I'd be happy to answer other questions too. And as we go through this task spot presentation, if you have questions, please put them there in the chat box, and Ricardo will help me, help notify me if they come up. So with that, let's get started, I guess. So Tar spot's a pretty new disease for the US, new since 2015. And in Michigan, our first findings of Tar Spot were in 2016. So as the name suggests, Tar spot, it is very easy to identify based on the name of the disease. It looks like tar has been flecked onto the leaves of the corn plant. See, here's a couple of different photos that you can see here. So, in 2016 when we first found it, it was very late in the season, around about September, and we were sorta hoping that it would just be a novelty and that would be the end of it in terms of its significance, but unfortunately in 2017 we had another field in Allegan County. So both initial reports were in Allegan, and in 2017 we saw a 40-bushel loss. We knew we had something serious going on, and in that instance, the photo there on the left is from that particular field and the plants were covered from top to bottom, so something very serious was happening. And singular occurrences were happening in northern Indiana and northern Illinois. Before I go on and give you a little more background about Tar spot, I just wanna talk briefly about the lesions, and we'll touch on this again just at the very end and hopefully that will, you know, clean up any confusion that might be out there. So, when we talk about Tar spot, we talk about this little black spots of tar that you can kinda see, what look to be tar on the leaves themselves. It will also talk sometimes about seeing a fish eye symptom. When we mean fish eye, it's just a little bit of dead leaf material around that tar spot lesion itself. Okay, so there's a few examples here. And what's just interesting about this is that in Mexico when they see this disease, they strongly feel that you have to have the fish-eye lesion to get severe yield loss. Okay? And they believe that there's two pathogens working together to cause that. So, so far in the US we've only isolated one pathogen. So my lab, USDA in Beltsville in Headquarters, Illinois, Indiana, Wisconsin, multiple other locations in the US have tried to isolate the second pathogen and we haven't found it. And the other piece of information that's important to know here too. In the US, essentially, that black spot, that black tar spotting is what we have seen that caused the yield loss. We haven't seen that fish-eye symptom being necessary for yield loss. Okay? So it's just important to try and clarify that in case there's any confusion and at least here in the US, that's what we've seen happen. Okay? And we've just isolated the one pathogen to date. Now, here's a closer look at that particular pathogen, and so it's just, it's called Phyllachora maydis. The actual name isn't that important, but that's what it is. So what we have here a couple of close-up pictures of that fungus itself, actually in the corn leaf. So on the left hand-side here what we've done is basically is take a corn leaf here and cross-section it, right? And so we've taken a razor blade and cut through that, and so what you're looking at is that black tar spot structure that's gonna be a raised structure to it. Okay? You can see it's pushed up the leaf material here and it's caused a lot of that sort of darkening of the pigment. That's the fungus itself through to the bottom of the corn plant and within that you can see this little ball-like structure, little round structure in there and so basically that is where all the spores are being produced of this tar spot fungus, this Phyllachora fungus. Okay? So if we look at the right-hand side, this is a real sort of close-up of those spores. And so these spores are produced just like they are in the white mold fungus or in Fusarium. So this is a type of spore that's pretty common in other fungi. And what's so significant about this is that these spores are produced in these little sacs, and there's eight spores in a sac, and the significance is that they're discharged, they're forcefully sort of exploded out of those sacs when there's humidity change. And so what this means is that this fungus can release their spores into the air and they can be transmitted on air currents and moved potentially long distances. And that's certainly what we've seen to date. That these things seem to be moving great distances really in terms of moving around and infecting fresh plants. And the other thing I'll just point out now and I'll try to reiterate it too is that this disease is pretty stealthy, and what we mean by that is that a spore will land on a leaf, it will infect that plant and you won't see that it's infected for a period of time. We don't know how long that period is just yet, but that can happen. Okay? And so, it's very different from northern leaf blight or gray leaf spot. For those particular diseases we typically see the lesion itself, and it's pretty easy to identify it, and that's really where the fungus in those diseases is restricted to, to where the lesions are occurring. But not in Tar spot. It looks like the plant can become infected and the infection can kinda move through the plant. And I'll show you what I mean when we talk about how quickly this disease can move. Okay? So just quickly to what we know about its introduction to the US. So it's first found in Illinois, in Indiana in 2015, and from there we've confirmed it in Michigan, Wisconsin, Iowa and Florida as well. Okay? And Ohio was just recorded last year as well in 2018. So it's definitely here and has spread around. So those are first years. It's really 2018 I think that really surprised a lot of people okay? And as I mentioned, we were familiar with this disease in Allegan County down here, Okay? So in 2016 we'd seen that late in the season, and causing some problems in 2017 in Allegan. But by 2018 the disease had exploded across about 27 different counties, Okay? And in some of these counties that I've highlighted here with these blue stars, are situations where we've received calls and growers are reporting around 50-bushel losses in those particular counties, Okay? And there's probably other counties that we don't have accounted for here. But just to sort of show you the spread of it and where it's been really impactful so far. And just driving around Macomb County in 2018 we really struggled. We weren't able to find a field with no level of Tar spot. So every cornfield had some level of Tar spot. So it's very widespread. We fully expect that this disease will appear in the thumb this coming season. Most likely it won't cause severe yield losses in the thumb and that's just because it's a new disease and the amount of inoculum of that disease is really important for how much damage it can do, okay? And so as a disease sort of sets in on a place and builds inoculum, it has the potential to kick-off a bit earlier each year provided the conditions are favorable for disease. And so we expect that most of the corn-bearing counties in Michigan will have some level of Tar spot this year. The level of damage is still you know, open for debate. But I'm pretty concerned by what we've seen to date. And I'll show you a couple of examples of that too. So just more regionally then. This is what we're seeing in getting together with other colleagues around the country here and figuring out where they've also seen it on a county level. So you can see it's really around Lake Michigan there. So it's spreading and it's very much fitting this pattern of an introduced disease. So an introduced disease will pretty much set up in its first location and then spread out from there and that's what we've seen to date. Okay, so we really don't know much about how this disease is behaving in the US. We've only had it here for a couple of years. So our colleagues in CIMMYT in Mexico, so that's an international research organization, agricultural research organization in Mexico, they did some modeling, and so this disease has been around for quite a while actually. I did some looking today, and I think there's reports from 1902 in Mexico, first description of this disease. So it's been around for a period of time. And so what the folks at CIMMYT did was looked at the weather conditions across Latin America and Columbia other locations where they see this disease taking off. And they took that information and they mapped it back to the US and our climatic sort of weather conditions to get a sense of where this disease is likely to be a problem based on what they could sort of infer from those data. And so this is what they came up with. And you know this is prior to us doing that map that we did around Lake Michigan right? So it's really laying out very closely with what we've seen to date. So unfortunately, I think, for our Michigan producers it's gonna be a problem we're gonna be contending with for a period of time. I don't think this thing is gonna go away. I've got some other information that those folks at CIMMYT were able to pull together for us. So monthly average temperatures between 63 and 72, so it's kinda like slightly cooler temperatures, high relative humidity like most fungal diseases, and some leaf wetness as well, so more than seven hours leaf wetness per night, and then those soggy days that they looked at, and rainfall too, that can be another component of moisture. Okay, so let's go through and look at how quickly this disease has progressed and why we are so concerned. So 2018 was certainly a particular year like every year is. These fields that I'm showing you are from out in Allegan County, about five miles or ten miles away from Lake Michigan, so they're very close to the lake. On the left-hand side there, you can see that a number of areas of this field were flooded out. So we had some water stress at the start of this season. I don't think that's the primary reason for this Tar spot having such an effect here because we've had lots of other reports of severe problems. But what I'm gonna try to point out to you here is how quickly it moved, and in this particular field we set up a fungicide trial too to get a sense of how fungicides would work for it and I'll share that information with you as well. So on the left-hand side here, what you can see then, apart from the obvious water damage where we're missing plants, is areas of disease as seen by the air. So by August 24, all of the corn plants in this field had some level of disease. But there were certainly patches you can see that were browning up from on top here, and that's all Tar spot all throughout this field, right, all those brown areas. When we look at this same area here that I'm sort of highlighting with my mouse, you look at that two weeks later, that area of heavy disease pressure ended up lodging. So for whatever reason, disease had really taken off in that section in that field a lot more intensely, and that had created severe lodging. So that's another very dramatic symptom of this disease. And just for note here too, the farmer noticed disease July 8. So things moved along very, very quickly. In terms of data, so to support what I'm showing you here, this is all information from this exact same field, right. It's just putting some numbers to the pictures I'm showing you. And so we've got a disease progression curve. So on the y-axis here, that's the Tar spot severity, and what we mean by that is we just look at individual leaves in a plot and we'll do a number of them, say like ten leaves in a plot and look at how much disease is on that leaf, okay? And in this instance we looked at the Ear leaf, in blue there, and two leaves above that, Ear leaf + 2 to look at how much disease is on that because we want to get a sense of where disease is in the canopy. And for this there really wasn't much difference between Ear leaf and Ear Leaf + 2, but what's striking is how quickly that leaf becomes diseased. Okay? So on August 10, when we went in and looked at this field intensely and set up a fungicide trial, at the very start there, every plant was infected. Every plant had some level of disease. But when we looked at an individual leaf, it only had one or two spots, or sometimes no spots of Tar spot on that particular leaf. This is important in terms of thinking about fungicide applications too, and the level of scarring we want you to be thinking about and thresholds for making a fungicide application. Then by August 24, our second rating, we saw around about 10% disease severity occurring on that plant and this photo on the right-hand side is representative of that. So we're estimating about 10% of that leaf area with disease. We came back September 7, and that whole leaf was essentially shut down, pretty much no green leaf area left on that plant and that's what we're recording here, nearly 100% disease severity. So it moved very, very quickly within a month from having one or two spots on a leaf through to a completely dead leaf, okay? Keeping in mind that all the plants in this field had some level of disease, but the severity was very, very low. So we set up the fungicide trial. Currently this is sort of current registrations that we have. So Trivapro is the only thing that's got a full label. But there are emergency exemptions for a number of other compounds and this is changing pretty quickly, so check back, but that's where we stand at this point in time, and we expect that some of these other products may very well get labels for use this coming, or full labels for use this coming season. So we took advantage of this field with this disease pressure in it. We set up a fungicide trial, and when we set this fungicide trial up, we, it's all something we can cart around in the back of our truck here. So it's basically a four-rowed sprayer that's on their backs, a back-pack sprayer. And so we're spraying four rows at a time and we're running plots about 30 feet in length. And that's ... the small footprint allows us to look at a lot of different products in a small area. And you can pretty obviously see where our fungicide trial was, right? So the whole field is dead by September 7, except for where we've run our fungicide trial. It's that green area down there. So when I went to set this fungicide trial up, I wasn't necessarily comparing a whole bunch of different formulated products, okay? That wasn't my first intention. My first intention was to try to look at the mode of action and what that's gonna do for us in terms of controlling this disease. What sort of mixes do we need to be looking at for disease control. And so I picked a few different mode of action chemistries or FRAC groups. And so I picked a Strobulirin chemistry, that's a FRAC 11, and for this example it's headlined but it could be something else, right? It's just that's what we had available, and that's what I used. We used Triazole which is a FRAC 3, which was the Proline, and again, I could have chosen a different product, but that's what we used. And then for the Premix, I used Delaro, and what's significant about this is that it's both modes of action, a Strobulurin and a Triazole in a Premix. And just to clarify really quickly, Headline is not equivalent to Headline AMP. They're different formulations. Headline AMP would be more like Delaro. It would be a premix. So I just want to point that out. The whole rationale here is to look at those mode of actions and to see what they're doing for us. And so this is a close-up of that field trial and you can see obviously where our control plots were because there is dead surrounding corn that did not receive a fungicide application. So you can see now where we put those fungicides on and what they did in terms of just a picture there. And we took data from this trial as well of course. I've got four sets of bars. I've got the August 24 rating where disease is there, and I've already talked you through the severity in this field. So it's there. It's starting to really kick in by August 24. It's gets really severe by the 7th of September. And there's two sets of bars for each date. One is the Ear leaf rating and the other is the Ear leaf + 2 rating, okay? And again, this is the disease severity. So how much of that Ear leaf or Ear leaf + 2 leaf had disease on it, okay? So if we look at these very right hand set of bars on this particular chart then, we can look at an untreated check and that's no different from the other data that I was showing you. So essentially 100% disease by the 7th of September. The Strobi chemistry, that Qoi FRAC 11 group did reduce disease somewhat, not statistically significant here, but it did reduce disease somewhat. And this is pretty much what we'd expect from a Strobi, so and we're being very unfair in the Strobulurin I should say as well. So we're applying it essentially after the plant is infected, okay? And you really shouldn't expect too much curative activity from that Strobi. The Stroubulurins are better at inhibiting spore germination. So perhaps if we'd applied that Strobulurin chemistry a little bit earlier on we might have seen better efficacy out of that, okay? And then in the gray bar there, that's our Triazole or a DMI chemistry FRAC 3. That did a better job because Triazole chemistries are better at curing a plant that's already infected. So if the spore's already germinated, started invading that plant, you put that Triazole on, it's capable of killing those infections, okay? And then in the yellow bar that's our Premix, and this is very much lining up with other colleagues such as my colleague in Wisconsin where you see those Premix chemistries seem to have the best efficacy out of all the different blends that we've seen. So that's definitely something that we would make recommendations on coming to this growing season. Uh, just -- - Hey Marty, I just have one question here from Eric. - Sure. - He's asking when do you think we would be able to start seeing the disease symptoms with the drone? You know, they -- - Yeah, that's a very good question. So with drones, I would say, so this depends on how severe the disease is, right? So here's another trick, Don't go using the drone to do your scouting. I really like the drone. I thought they were really helpful for us this year, especially scouting corn. Definitely, I would take advantage of them. But the other trick is to get out and walk the field too, and just see what you can see. Even if you go looking for those potentially bad areas from a drone imagery or a satellite imagery, you've got some areas of stress in the field. That's definitely areas to check. But I just say that because you might miss some of the early symptoms if you just fly looking for those brown spots, okay? - Right. _ And I'll show you some photos at the end there. We could talk about that a little bit more. - Awesome! Thanks so much! - Yep. And so here's just a photo to show you in terms of standability of the plots, okay? So untreated on the left side there, you can see it's lodged and the tops are swollen and on the right hand side, that Premix with both modes of action better standability of that particular corn. We did try to take this through to yield, but unfortunately because of the water pressure at the start of the season, the flood damage, the stand was so uneven that in our 30-foot strips we just weren't able to take many full-yield away. However, having said that, based on the photosynthetic area that we were able to preserve by the 7th of September, I wouldn't be surprised if we saw a 30-bushel protection from those fungicide applications, okay? And so, yeah, this sort of brings up the question, when to make a fungicide application. Okay? Obviously, this depends. The ideal timing really depends on a number of different factors, such as the amount of disease pressure, the current environmental conditions, and a couple of other factors including economics and what you're capable of doing in terms of those applications. So, if you were to make a vegetative application, a V8 application or something. If disease is present, that might be helpful, and it might suppress disease, but if we're relying on that V8 application, it's not gonna be enough to see us through the season, okay? Because we still got quite a bit of the season to go. An R1 application might be the best bang for our buck, so if we really can only make one application, we're guessing that that may well be the best application, but we still don't, I mean we don't know yet. This disease is so new to us. We certainly want to protect as much of that photosynthetic area as we can, so that might be something to consider. In some situations where there's heavy pressure we've got very susceptible hybrid and where the conditions are just really unfavorable, there's a potential that you know two applications might be necessary. And then the question to ask is, "Is this gonna be economical?" And I think again, I mean a really important piece of this is scouting, knowing what sort of disease pressure we have present in the field and in the surrounding area, being aware of the situation in the neighboring areas as well. So be aware of the pressure in your particular field. Okay, with that let's switch over to discussion on hybrid resistance then. Now so here's a couple of aerial photos showing you differences by hybrid, okay? And some of this is a little related to the maturity of that hybrid as well, and we can talk more about that. There's definitely differences by hybrid in terms of sensitivity or susceptibility. So we went through and we did disease rating on the Allegan Corn Performance Trial Site. And so I would call this a low-to-moderate pressure location, okay, so it wasn't a really high pressure location such that the corn was falling over or we had, you know, plants completely covered in disease. Not by any means. But there was pressure there, so we took some rating. So there's two different color bars here, by hybrid. The orange bars are showing you how much green leaf area is present, so it gave you a score of how much green leaf area was present. And then the blue bars are how much Tar spot, how much at the canopy had Tar spot to it. Okay? And so you see we had some hybrids with almost 50% Tar spot on the foliage and we had others with almost nothing. Probably about 1-2% with that leaf area with Tar spot, okay? So what we're seeing is that there are differences in the hybrid, so that's great. That gives us some hope that we can breed for resistance. However, the trick here is, and I'm sure if you talk to your seed salesmen, they're gonna be struggling here as well because this disease is so new. We need a lot more rating data. So we saw that even some of these hybrids with fairly low ratings, we share this information back to the companies and they came back to us and they said, "Oh this hybrid, even though it looks okay in this trial, had the lower rating. It fell over in our location." Okay, so the problem is in areas with higher disease pressure this little bit of disease resistance we saw was not enough. So we definitely need to do some more breeding and that's part of the project we're involved in at the moment. And the other important thing just to notice, and this is true for everything that we've heard so far, is that there is no hybrid that is immune to this disease, okay? So every hybrid will get some level of this disease. Okay, looking at yield loss. So we were able to take this data from Allegan performance trial site, and here's what we were able to come up with. So it was quite a good-yielding site, right? 200+ bushels per acre. So we plotted essentially just yields here on the left-hand columns against the Tar spot severity. And we did that with the early maturity group and the late maturity group that the hybrids were split based on 102 day. And so, what we were able to see here there was a correlation between the amount of Tar spot severity and yield loss or yield, okay? And so essentially what we were seeing was for every 1% increase in Tar spot severity, we were losing half a bushel. So at 10% Tar spot severity, we were losing 5 bushels. And speaking with colleagues, you know, they were seeing up to .8 bushel loss per every 1% Tar spot severity, so that the line to these slopes can be even steeper, potentially on the situations where disease pressure is more severe, it may have started earlier in the season. Okay, so this is a very real disease and we definitely need to do a lot of work in terms of breeding for resistance. In terms of impact on corn silage, we thought it would be a good idea to have a look at that. We weren't able to collect any replicated data but we did visit this particular field and took some samples from a heavily infected area and then compared that to an area that still had disease, but just less disease pressure, okay? Cause we're getting a lot of questions. Well, what's this gonna do to the corn silage quality? What should we be concerned about? I guess one thing, off the bat too, is harvest stability. I mean when disease really sets up, it can lodge and make things really hard to pick up. And this particular field, to our knowledge, is really Tar spot. We visited this. Tar spot was really the driving factor. There wasn't anything else that we were really aware of causing these lodging issues in this particular field. And just in terms of grower perspective, this particular farmer noticed that the bottom end of the shear looked like it had been frosted. That's how it sorta looks in August or late August, the frost is coming. But that's the Tar spot just shutting those plants down. Anyway, so we've got two areas here, a severely affected area on the right-hand side that's lodged and we took some samples from that, and this less affected area, just to show you a closeup. And the really dramatic thing here is the stalks. Okay, so this less affected area, we've got some green leaf area still, but the stalks have still got a lot of integrity and moisture to them. Where the plants are lodging, there's just nothing left to the stalk. They're just, you can bend them very, very easily with your hands, and any corn that's still standing basically you just touch, and it's just falling over. So it's a really a big problem. Looking at just those two samples that we took, here's what we found when we sent it out for analysis. So the most striking here is moisture, and it makes sense, right? when you look at the corn. The severely affected corn was down to less than 20% moisture. So that means it's too dry to ferment. You gotta be at like 40 to 60% moisture. That less affected area was at 52% so still fine for creating silage or making silage. And then the other components too, it's affecting the quality of the feed, so not only are you losing yield, you know, potentially the stuff is basically being eaten by the fungus but the quality is down so the amount of cellulose and lignen is actually increased where this fungus has already gone through and really set up severely, and then the energy scores too are somewhat down as well. The one piece of good news here is that there are no associated mycotoxins, okay? So this is very different to Ear mold in corn where we're also really concerned about the mycotoxins, and the potential need to add binders or something to the feed that will take that out of the system, the toxins that have been produced. So again, Tar spot, as far as we know, doesn't produce any mycotoxins, so that's the one piece of good news. Okay, in terms of agricultural management practices it looks like rotation and tillage really offer little benefit. In discussion this winter with different growers ... Actually, let me back up a little bit. That field I was showing you before, that was under a corn/soy rotation. So that grower had Tar spot in 2016. He rotated to soybean in '17, came back in '18, planted corn and the field was decimated with Tar spot, Alright so, the rotation really offers little benefit. I spoke to other growers this season that used moldboard plow and that still didn't help them out. Okay, so it's gonna offer little benefit. Having said that, if you are continuous corn or no-till you will be at greater risk for a faster set-up of disease because you have inoculum right there and it'll be ready to go. So you might get a week or two jump as opposed to a field next door that might be moldboard plowed. I don't expect that field, the moldboard plowed field to escape disease, but it might be just a little slower in getting started and certainly not worth the moldboard plowing. The other thing that was really striking here is that irrigation favors infection conditions. Okay, so I've got a couple of examples. So Jim Schaendorf was good enough to share his experience. He was 150 bushels under irrigation and 212 where he did not irrigate them. Everything else about those fields was the same. So we're looking at a 60-bushel loss just by pumping water onto the system, okay? Let me go show you this other good example. So Bruce Macala put this example together with Jeff Struck for Prairie Ronde township in Michigan and what we're looking at here is an aerial image of course, of this field so you're gonna see the pivot, and he's got his dry corn in here as well, okay, near what we wanted to point out in terms of the contrast between irrigated and non-irrigated. This is his planting map, okay, so you can see the different hybrids that Jeff has planted into this field. Now I just put that in there just to show you when we're looking at the NDVI image what that means. So these green areas here are due to a different hybrid, and perhaps it's a later day maturity. Actually, it is a later day maturity, so that might be partly what's to do with the greenness of the canopy, but anyway the point of this story is about the impact of irrigation. So, we've got areas of the same hybrid in this larger area here and they were coming out at about 170 bushels under irrigation. This dry corner's about 220 bushels, okay? So again, about a 50-bushel difference, just by the difference of not irrigating, right? We're having those dry corners, much larger ears compared to those areas where he did irrigate. And the other interesting thing here is when Jeff did irrigate, he only irrigated twice in the season for this particular field, okay? So we did certainly have in southwest Michigan a lot of precip through the season and here's some data that Bruce was able to pull together. So there were a lot of precipitation events, so we didn't really have to run those irrigation center pivots, okay, the irrigation. But what's really surprising to me is that with just two irrigation events, we can see a 50-bushel loss. So this really speaks to the moisture that this fungus really likes. Unfortunately, it's a very aggressive fast-moving fungus, so if it gets those right environmental conditions, it can really hit hard, okay? For the rest of the state, you know June and July were pretty dry this season, so if we have more moisture this coming season, you know maybe that'll mean the disease will set up a bit earlier in those other areas where we have inoculum already building. So, we're concerned, even if it's more of a normal year, this coming season. Okay, back to scouting then. I've got a couple of different images here just to show you what it can look like. So the slightly sort of contrasting symptoms that we see, but it's pretty easy to identify. You should be able to feel those tar spots, those little rice bumps, okay? It can form on the husks as well when pressure is high. Okay, little black spots there too. And then, back to that fish-eye symptom, we do see this out in the field, but not to the level where we're like, "Oh, that's the fish-eye that's killing everything." It's really the tar spot symptom itself seems to be killing the plants. But just so you know, we can see it really sort of very clear, tar spot fish-eye symptoms at times. And again, as Ricardo and Eric were talking about, definitely scouting from the air can be very helpful. And so this particular field here, I guess when we're looking at this field, we were walking around a lot of it, and we could see some of it in some areas and not in others, but yeah, certainly once we got up into the air, it was very obvious there was something bad going on in some areas. We had these brown areas of tar spot, heavy pressure forming. So certainly if you have access to a drone, it wouldn't hurt to get up and have a look, or if you use any of the satellite or other aerial imaging services. You know look for the stress areas of your field in those NDVI or color images, and get out and scout others, but I think the key this year, like every year, is being aware of what's happening in your field. We can't really stress scouting and being aware of your field is very, very important. So just a quick recap, what do we know? The disease is caused by Phyllachora maydis, so really just the one pathogen here in the US. It's an obligate, that means it needs corn to reproduce on, and that's also a problem for us. So in the lab, we like to take a lot of these, look at all these systems in the lab and try and figure out what's going on with them. But we have to basically take it from corn and put it on corn. We can't grow it in the lab because it needs corn to reproduce on. The big problem is that it can survive on residue. And so it's just very happy surviving on residue, and we've got materials in the lab from last year, just dry leaf material. As soon as we put that into a moist environment, a moist bag or a moist chamber or something, it starts producing those spores. So it's just sitting there waiting. Obviously, you know, residue will start breaking down, and as that happens, other microbes will come in and start eating that fungus basically and it won't survive as well. But there's gonna be enough of it to survive and we've certainly seen that over the last three or four years now, that this has been here and it's here to stay and it is residue-borne. It does not need other diseases to infect, as far as we can tell. It's really just this Phyllachora that's causing all the damage. So you don't have to have gray leaf spot or northern leaf blight for this disease to be a problem. Having said that, of course if there's other diseases in the field, of course you know they can work together to have a greater impact on your corn plant, so you need to be aware of those too. It's not seed transmitted as far as we know. That looks to be pretty well-supported, and obviously the hybrids differ in their susceptibility. So what we're doing this year, we're gonna set up some pretty large field trials. We're gonna be looking at the spore release, plant infection, when is this occurring, can we help advise you as to when we should be making fungicide applications. We'll be looking at fungicide efficacy. So taking that we've got a lot of compounds, about 18 to 20 compounds that are in the lineup, side by side and see how they perform. And the fungicide timing program as well. We're gonna come in at different times for the season. We've got about six or ten different timings where we'll come in, different times to see what is optimal, and use that also to develop predictive models and spray models to help advise you on that. I'm stressing promising leads there already, and of course screening germ plasm and hybrids for all that. If you ... so anyway ... yep ... and we're looking at agronomic practices, how they drive disease. We expect that under really high fertility conditions, that's gonna help drive disease. It's not gonna be the number one factor, but that will drive disease. High density plantings too will also help to drive disease pressure. So with all these unknowns, a couple of things we can do then. One of them is to try and diversify hybrids. We don't like to see you just planting one or two hybrids cause you've got all your eggs in one basket. Obviously, there is not enough information out there, but to try and spread that risk, and grow a few other additional hybrids on the farm to help transfer that risk. And then, also consider hybrids with higher stalk strength to try and reduce that lodging. Avoid planting in the corn wind where possible. That just makes sense, but we know it's not always possible. Scout. Know what's going on. Apply a fungicide. We'll be making ... we already have a first-generation model, courtesy of Damon Smith at Wisconsin, and some of the data he collected and some of the data we sent him. We hope to make some potential recommendations this season. That's not quite ready to be fully launched yet, but we'll get the word out if we see conditions developing that look very favorable for that. If you're gonna need a foliar fungicide application, R1 is most likely to provide the best protection. With that though, you wanna manage your expectations, right? I know a few growers this year that did spray their field at R1 and the field still looks terrible, and that sucks, I know, but I'm sure if we hadn't sprayed at all, things would've been a lot worse. Okay, so manage your expectations. These fungicides are great products, but they're not silver bullets. They're not gonna eliminate disease, right? They will help suppress disease. Where we can with irrigation, we want to try to limit canopy moisture, okay? So frequent irrigation passes are gonna be a bad idea. And you know, perhaps, trying to be creative about that, maybe you know starting the pivot at like 3 o'clock in the morning and then shutting it off as day breaks or something to help try and limit moisture. And obviously the difficult one that we'll be putting out more information as we get it this season. And the other final thing to think about too, if you see those frosted area of tar spot set up, you might wanna think about harvesting those areas a little bit earlier and paying just a little bit for the drying cost unless you wanna be trying to pick that stuff up after it's fallen over, after it's lodged. Because that's another concern that we have right here, that all the excessive lodging, and that'll really happen where disease sets up and it's really severe. We see that sort of, you know, a lot of dead corn plants out there, so be aware of that. And with that, I'd be very happy to take any questions that we have. And, I always get a question as well, I've been meaning to pull this off of Twitter. Here's a picture of, from Twitter here, Jim Donnelly, he's and agronomist with DEKALB down in northern Illinois. So he took a picture here. It must've been the 18th of September last year, it's of a V3 volunteer corn plant, and you get up really close to that, you can see the tar spot lesions forming on that plant, So we get the question how soon, how early can that plant become infected? Well, if weather conditions are right, it can infect pretty early, okay? Now, maybe if that plant's coming up in May, it might be too cold for the fungus to infect, but when conditions are right, it can infect young corn plants.

You Might Also Be Interested In