Dr. Dean Malvick, U of M Extension plant pathology specialist and crops program leader and professor of plant pathology discusses corn and soybean diseases he has observed and what might yet appear in 2022. Since it was first found in Minnesota in 2019, the fungal pathogen that causes tar spot in corn has spread from southeastern Minnesota to as far north and west as Stearns County in three growing seasons. Tar spot-related topics included scouting strategies and identification, when symptoms are likely to be observed, and what research has told us regarding proper active ingredient and application timing for managing tar spot with a foliar fungicide.
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Ryan P Miller: We do want to welcome everyone back.
Ryan P Miller: Today, on the program we've got my counterpart Angie Peltier from Northwest Minnesota and she's gonna be guiding the discussion she's got a.
Ryan P Miller: long history with implant pathology and we also have pine pathologists and D malbec from St Paul to kind of drive help drive the discussion today so.
Ryan P Miller: Without I do want to call out thanks to sponsorship for this program today both Minnesota Corn Research and Promotion Council as well as the Soybean Research and Promotion Council and thanks for their generous support this season, to keep keep things moving here so with that.
Ryan P Miller: ask what comes to mind so with that i'm going to turn things over to my counterpart after I make just a couple brief comments angie.
Ryan P Miller: You know we've got a project down here in southeast where we do some some different demonstration research trials, as well as keep tabs on things in the field we've got a student intern this summer and he's been scouting fields for us and southeast Minnesota.
Ryan P Miller: Looking at various things and before I forget sorry kyle a little off topic, but we've been kind of keeping tabs on things, because the spraying activity is really, really picked up and and so he's been monitoring some fields and.
Ryan P Miller: first thing I want to mention is the soybean aphid over the last handful of weeks he's been monitoring things initially we found a.
Ryan P Miller: Few plants with higher numbers and then that kind of dissipated, and we had very, very low almost undetectable levels.
Ryan P Miller: And then earlier this week we started to pick up a handful of plants that were getting up in that 40 to 50 range, but a lot of zeros to so.
Ryan P Miller: You know if you're out selling your fields and wondering wow what's all this free activity going on, you know that's a just want to bring that up that we're scouting some of these things and.
Ryan P Miller: And that's where that's it now Dean has got a set of central plots that we planted this spring, with different hybrids and you know Tara spot, which is the topic of the day.
Ryan P Miller: We plan, the central high print hybrids for your Dean and i've looked through those a handful of times now, and just not seen really any incidents of tar spot or any other corn leaf diseases so just kind of a brief synopsis of what we've been seeing when we get out in the field.
Ryan P Miller: At this point in the season, we start them at monitor those late season insects and diseases that can come in and be eliminating certain circumstances, but with that I want to kind of pass the torch over to angie if she's got any comments to make.
Ryan P Miller: And then we'll kind of move forward with a discussion on Tara spot and take questions and go from there.
Angie J Peltier: Thanks Ryan i'll just give a little report about what i've been seeing up in the northwest of the state.
Angie J Peltier: Are soybeans couple of weeks ago now began to pull out of iron deficiency fluorosis symptoms so they're trying hard to close roles and.
Angie J Peltier: Other than IDC we see a little bit of bacterial blight but a very little bit and otherwise the the rest of the the soybeans are pretty clean I have yet to find my first soybean a bit, but i've also yet to.
Angie J Peltier: check my my usual spots where I would expect to see him first and that's right next to.
Angie J Peltier: right next to some wooded areas right alongside of fields, so.
Angie J Peltier: In the corn again also pretty darn clean, this time of the growing season, although I would expect that some of the people that have gotten some hail and strong winds.
Angie J Peltier: You know, we might be seeing some patches of gases blight symptoms start to show up here if they haven't already, and in those instances.
Angie J Peltier: Dean, what have you been seeing on on your travels throughout the state.
Dean K Malvick: yeah that's you know with the highly variable weather across the state, certainly the conditions that people are reporting and both growth, growth and the seasons, is quite different.
Dean K Malvick: In the south west South central even some reports of significant quite off their issues and swimming and some fields, which is interesting.
Dean K Malvick: We don't see a lot of large outbreaks i'm not sure how large that it is, but I heard he reports we've had some razak Tony and some of our our plots or irrigated.
Dean K Malvick: Just kind of illustrating again the risk of that disease, when we have lake planting and high soil moisture.
Dean K Malvick: i'm again I don't think there's been a lot of that and big scale, but something that pops up under the bed conditions.
Dean K Malvick: and other than that on soybean I haven't seen or heard of a lot certainly bachelor of blake is prevalent many fields now, including here in St Paul.
Dean K Malvick: Not anything to be really concerned about in most cases, so, for your brown spots fishing a little lower leaves is there in many fields, as it always is.
Dean K Malvick: Again, nothing to us to be concerned about on corn not not a lot of major issues Certainly this is usually about the time that corn diseases start to take off, as this truth so even diseases.
Dean K Malvick: In early August mid August, not a lot of major or even minor issues that i'm aware of i've seen rust up there for sure i've seen some really lesions in northern leave blank.
Dean K Malvick: And, of course, the one of the big topics that's a lot of people are concerned about is our spot had reported that and southern free born, excuse me.
Dean K Malvick: So mark counties that was impressed me was a couple weeks ago and we have other reports now from free born in homestead so it that that disease is starting to develop.
Dean K Malvick: As we kind of typically think now in early August not high levels anywhere but, overall, the big picture of corn and saving diseases i'm not aware much happening that's a highly significant nature right now.
Angie J Peltier: So you both mentioned tar spot, and I know that that that that particular disease has been a.
Angie J Peltier: Pretty big issue, particularly in what years and has the last several years, its range has been expanding in the state, since its arrival of what three years ago, is that Dean.
Dean K Malvick: Yes, all of 2019 is first found in southeast Minnesota.
Angie J Peltier: Great not great that it was found, but thank you for that answer, can you please provide us with what what the state of our knowledge is about this particular disease how how it spreads how best folks have have found to manage it, and then our do we have any options for our.
Angie J Peltier: corn crop do we have any way to prevent tar spot in epidemics.
Dean K Malvick: Okay, and yeah i'd be glad to provide a bit of a summary I think a number of folks are certainly familiar with the disease.
Dean K Malvick: And I want to some are not and there's still a lot of mystery I think surrounding this so i'm going to cover a few the the main points I think are important to keep in mind not to go into this in great depth.
Dean K Malvick: Again, what I want to cover, very briefly, is what is our spot where is it a little bit about we know about the spread and scouting and then, what do we know about management.
Dean K Malvick: And so Tara spot, there are a few basic facts and keeping it is a fungal disease so unlike goss's wilting this can be managed at least to some extent with fungicide applications.
Dean K Malvick: And the name is very.
Dean K Malvick: descriptive because the spots, the legions the fungal structures produced on the leaves by the disease are very black black a star and very small easy just a few millimeters in length.
Dean K Malvick: and coordinate all growth stages is susceptible to infection in our first reported this.
Dean K Malvick: sort of this year was actually the last week of June roughly I think the six corn at very low levels, but still, it was found.
Dean K Malvick: In fact, recording residue is certainly the main source of binoculars, I think, and in all the places so far in Minnesota and I think probably in other states with the disease and found so far.
Dean K Malvick: it's been found in fields where the disease has been present either they are very nearby, so I think.
Dean K Malvick: The more knocking them will have in the city of that field, the more likelihood will have early infection and also more likely will go up high levels.
Dean K Malvick: But we also know the path that you can spread by wind and we don't have a good understanding yet how far that can spread.
Dean K Malvick: And then diseases favored by cool and wet weather in some ways that may be similar to the weather that favors white mold this disease tar spot does not do well under dry conditions.
Dean K Malvick: And just a bit of a review, where the disease has been found now again, it was found for the first time in the US in northern Illinois in northern indiana.
Dean K Malvick: Since then, it spread across much of the corn belt across all of iowa cross much of Ohio pretty far up into Michigan and Wisconsin and down for southern Illinois and indiana and as far east as Eastern Pennsylvania so it's been spreading it's been increasing.
Dean K Malvick: console from some folks certainly a wonderful, whereas if and found so far this year, there is a map it's on, if you look it up it's Minnesota let's see that corn.
Dean K Malvick: I PM pipe.
Dean K Malvick: corn I PM pipe you can look that up on a website, and you can see a map they're showing the current confirm distribution of tar spot across the US.
Dean K Malvick: And the current map shows and number of counties where has been found again all in areas where it has been found before.
Dean K Malvick: Generally, what we're finding when we find it new counties it's a little later in the season, this is driven probably by two things spread of spores from areas where three prevalent to new areas, as well as the weather conditions that would favor if.
Dean K Malvick: And so again it's been spreading in Minnesota we can focus on Minnesota it was fine for the first times, three years ago, in the very southeastern States Senate Fillmore county and, as a last let's say at this time last year we knew it to be as far North and West is a sore county.
Dean K Malvick: But by the by early October, we had found it and confirmed it as far as Stearns count.
Dean K Malvick: Again, there are some certified observers looking up in that part of the state and they found it at low very low levels, and some link planted corn was still bring in early October.
Dean K Malvick: So again, we know that disease is spreading and we don't really know how far to spreading you think about how far we know it's spreading in roughly two years se the roughly central Minnesota.
Dean K Malvick: It could very easily be a well into the middle of the River valley and probably yours if it's keep spreading at the same rate.
Dean K Malvick: that's pure speculation, we don't know how far it will spread nor a best.
Dean K Malvick: And so early in the cycle at this time of year, and a lot of fields it's going to be hard to find this initial spots are just black.
Dean K Malvick: elongated raised spots and leaves that that look like insect grass and dirt and other things, all of those others can easily be wiped off typically with a finger.
Dean K Malvick: And I was in a field yesterday, looking at some spots on leaves thinking Oh, is that tar spot and looking closer and wiping my finger across that leaf in those spots came right off, and it was very clear it wasn't.
Dean K Malvick: And so, in my plots at rosemount where I was yesterday there was no to our spot I could find we found it later there in the year last year.
Dean K Malvick: So it can start out with just one or two these spots on leaves to tune a few more so it's not necessarily easy to find the first stage.
Dean K Malvick: And the disease key point is that the disease can develop pretty rapidly from leaves with just a few.
Dean K Malvick: Of these spots to leaves covered and leaves killed now in two to three weeks under the right conditions so Hence, it is a disease, we need to be really watchful.
Dean K Malvick: And it's an easy thing for me to say at this point loss scout the fields and then respond, yes, we can do that, to some extent, but of course and alerts cornfield and early August.
Dean K Malvick: it's not easy to see every place where it could be developing you know can develop and patches in the middle of fields and spread from there.
Dean K Malvick: So this is a bit of a challenge, the fact that it can develop quickly under fairly quickly, maybe we could say under the right conditions, but also not necessarily easy to scout for.
Dean K Malvick: And just a few points about how the disease develops again we think probably in most fields in Auckland is coming from within the fields, although we know it can spread from outside the fields.
Dean K Malvick: But most of the early season infections probably coming from within the field and from very close those force from that residue and the fungus growing on the residue if it's infected would go up on the plants new plants.
Dean K Malvick: In the middle of summer under wet conditions, you know, in fact, the plants and then.
Dean K Malvick: Within 14 to 21 days those black spots, those are spots, develop and then new sports can develop from those and the disease can cycling, the field and that's where we have real concerns the secondary epidemic development.
Dean K Malvick: And what are some risk factors that we know we still have a lot to learn about cars, but.
Dean K Malvick: It doesn't Act, the same way and then us in many ways, as it does in Central and South America we're at this study much longer.
Dean K Malvick: So what are some risk factors, if our spot was in the field, or area last year, the late planting.
Dean K Malvick: Because the disease does seem to be favored by later season conditions, who are whether we're do that kind of monitor temperatures high relative humidity standard leaf wetness heavy dues frequent rainfall in the morning for those are certainly some of the factors that favorite.
Dean K Malvick: and water is a significant driver seen pictures, for example, from Michigan where Center pivots very under the Water have high levels of tar spot and other areas outside of that you're getting dope so so we know that water is an important part of the disease development.
Dean K Malvick: And what about managing few key points, I think, first of all, we need to scout word.
Dean K Malvick: Ideally, and out, I would have thought late July because we hadn't found it or before late July prior to this year, but now it was found in late June sure so i'd say start scouting.
Dean K Malvick: And we're past early July this year, but third scouting anytime after early July to figure out where the disease development.
Dean K Malvick: And to think about if they needed on your site application, where the likelihood we needed this highest because earlier that disease develops, the more likely the disease could develop the damaging levels, first, that all depends on the weather.
Dean K Malvick: nothing we can do is avoid the most susceptible hybrids more see companies are identifying hybrids are significantly lower and susceptibility and I can definitely make a difference, fungicides can be effective.
Dean K Malvick: But they need to be applied when the epidemic starts.
Dean K Malvick: and timing seems to be some time and to be to our to our three wins is probably the best timing and for those fields that are irrigated you know your gate as infrequently as possible.
Dean K Malvick: to minimize the wetness.
Dean K Malvick: and
Dean K Malvick: Again, the best timings seem to be that vtr too so we're at that time of the year, right now, as we all know, and many different fungicides work there is a website of the crop protection network.
Dean K Malvick: there's a table on there with.
Dean K Malvick: fungicide advocacy.
Dean K Malvick: ratings for a number of fungicides for Tara spot and number of other borne diseases, so that is something useful to look at.
Dean K Malvick: And again that's the proper protection network on decided advocacy tables.
Dean K Malvick: And for more information on part plantar SWAT proper protection network has it pornography and pipe I mentioned that that is a source of math and distribution of the disease updated fairly frequently.
Dean K Malvick: I will stop there, in terms of the general background i'm.
Ryan P Miller: Studying I like.
Angie J Peltier: Oh.
Ryan P Miller: So staying on the spot theme.
Ryan P Miller: Dean, is there anything to caution folks about you know it's it's real challenging to find these investigations and so there's.
Ryan P Miller: there's sort of you know people assess risk in different methods and so sometimes folks will just decide i'm going to its vt let's put a bunch of sight on.
Ryan P Miller: And what do you is there anything to caution folks about this particular disease and and that strategy, I mean is my concern it on at that point, or what are the things to think about if that's my strategy.
Dean K Malvick: yeah I mean ideally we wouldn't apply, and so we knew the disease was developing field.
Dean K Malvick: And we saw weather conditions and look favorable.
Ryan P Miller: And so you know in southeast Minnesota they think you know we're we've got a hot week but overnight we're cooling off, you know and that dramatically but we're down in the 70s, I would, I would say, and.
Ryan P Miller: Are those conditions still pretty conducive would you say because we're not like you know, at least in other parts of state i've been so so far we're things seem to be kind of.
Ryan P Miller: dying, now we.
Ryan P Miller: We have pretty good moisture down here.
Dean K Malvick: Right, I would say there's some areas that are that are definitely very favorable and when I can tell.
Dean K Malvick: I can say that we saw developing and areas, you know not too far from Rochester last year, certainly didn't get a lot of frequent rain.
Dean K Malvick: They have adequate range support the current growth, but it wasn't certainly a wet year and some of those locations and still developed a pretty significant levels, although it was later in the year that are really took off.
Dean K Malvick: And the other point I think in terms of the question about the French side application, the tea again since this disease terror squad often develops later when it really ramps up.
Dean K Malvick: Sometimes the vt application will run out of some of its protective power by the time the disease really takes off.
Dean K Malvick: So unless we have a reason to think that meet the application is needed, it might be wise, we think we need to apply for our sport to wait a little bit longer are one or two.
Ryan P Miller: So Dean has has there been worked on on on the residual length, you know of advocacy for this particular disease or you know, has anyone tried to examine that like.
Ryan P Miller: You know if I put a fungicide on how much time does that.
Ryan P Miller: ballpark by me.
Dean K Malvick: yeah you know that's that's not easy to answer, because we know there are many different fungicides out there, different formulation different active ingredients and they can have different residual activity.
Dean K Malvick: levels are timings.
Dean K Malvick: From observation other states i've heard two to three weeks might might be pushing it in for many fungicides.
Dean K Malvick: So.
Dean K Malvick: So that's not a very scientific study supporting them.
Ryan P Miller: Well, it gives us kind of a ballpark idea I think we're we're protection me how long may reside, but.
Ryan P Miller: So Dean kind of along along those lines, you know Thinking forward we got a question that came in about the tire spotter APP.
Ryan P Miller: kind of predictive model of you know risk helping us assess risk, if you want to talk about that its utility maybe for Minnesota and anything else that you guys in your lab are working on to you know, try to help manage this disease, if you just want to take a couple minutes.
Dean K Malvick: yeah a couple points are spider APP so you know about that.
Dean K Malvick: it's developed at the recent Wisconsin Madison it's a predictive tool available as a smartphone APP that you punch in your location GPS put in a number of the other variables planting dates rap stage things like that it comes up with a risk of tar spot.
Dean K Malvick: Okay it's i'll say I two things we're still learning a lot about our spots are some of the variables, I think, are subject to some change.
Dean K Malvick: it's been shown to be used, certainly useful in some places, I can say this, we looked at it yesterday for rosemount, for example, and it said, the risk was well above 90%.
Dean K Malvick: yeah it's been quite dry there and.
Dean K Malvick: Certainly, I would say not that favorable for our spot, partly because there isn't a strong history of top spot there.
Dean K Malvick: I think that's a really important driver here we don't have a real clear history of tar spot in a particular field and you're by.
Dean K Malvick: The risk the even this early in season is probably not real high, so I think the prediction was wrong and that location, but if we use it down further south.
Dean K Malvick: we're talking about is more prevalent se, it may be more accurate, I think we still have some learn I think that's something that's useful to look at assessing your own situations how useful it's going to be.
Ryan P Miller: yeah so you have to have your own kind of.
Ryan P Miller: interpretation on it, I guess, just kind of it's your potential and think about it, not just rely on the tool yeah.
Dean K Malvick: that's right, I mean really key thing is this disease, we know is driven by the weather as i've mentioned, especially rainfall and moisture.
Dean K Malvick: And you know this APP car spotter uses a network of weather stations that they that's feeds into it and I suspect, in many cases the nearest weather station is not close to.
Dean K Malvick: Some particular fields, and we know whether it's highly variable variable possible at landscape, so I think that's one of the reasons why.
Dean K Malvick: We have to look at this carefully.
Ryan P Miller: Regionally Dean has anyone looked at, you know if we're in an area like in southeast Minnesota or even the central part of the state where you see a.
Ryan P Miller: You know, a higher number of corn on corn acres or higher you know percentage of acres being more years of corn from you know the livestock aspect of things, does that increase risk for a region versus somewhere that might be.
Ryan P Miller: more of a 5050 split or you're getting more acres of soybean or does that not matter really.
Dean K Malvick: It it does seem to matter, especially with the earliest infections.
Dean K Malvick: Although we have to think about it, in fact, that we know this disease can spread from other fields i've seen it myself and fields in southeastern Minnesota that were in.
Dean K Malvick: Savings previous two years, and yet tarps work developing fairly high levels, but they were also very near other Cornfields or other fields that had been previously.
Dean K Malvick: So I think the regional aspect is very important, as well as the local field aspect.
Ryan P Miller: Well, good um I did just to mention here, I did put to the links in the chat stream here that Dean and mentioned and they're both on his slides here, but the crop protection network.
Ryan P Miller: Again, if you're if you're listening to the podcast you students right upset you know if you Google crop protection network, you can quickly click to this fungicide advocacy in corn, and they also have some other crop information on that website, but.
Ryan P Miller: Crop Protection network good resource, as well as that corn I PM pipe which gives us some kind of distribution information on various diseases and that link will actually take you to the.
Ryan P Miller: The lead landing page for recording diseases in in the US so kind of some interesting tools for folks to look at things and see see what's out there.
Dean K Malvick: yeah I mean, I want to make the point again that I think it's really important to do some certified scouting born cross.
Dean K Malvick: At this point, especially central Minnesota Rochester Minnesota trying to figure out where this disease is spreading developing screen, it may not be a significant issue in any of those places this year.
Dean K Malvick: But knowing where it's developing this year will know that the risk is greater featuring years so again, especially in areas where it's been raining more frequently.
Dean K Malvick: Everybody can use their sharp eyed scouting skills, so they look for this would be really helpful for everyone.
Ryan P Miller: Indeed, this is something even at the time of harvest when things have progressed to the point of any potential you'll less you can still see this disease right and you could do some assessment at that point in time.
Dean K Malvick: You can, but I have to say it unless it's a high levels it's tough it's much harder to recognize that.
Dean K Malvick: it's easier to see on green leaves for sure.
Ryan P Miller: And you know just another question I guess what what potentially you think with the infestation that started and things were conducive for disease development regeneration what kind of potential impact could you have on annealed I mean, is it widely variable or you know.
Ryan P Miller: let's say something started right now, and things remained in a good, you know spot as far as development.
Ryan P Miller: As far as the environmental.
Dean K Malvick: Their reward some other states.
Dean K Malvick: At least 40 or 50 Brussels you lost they're estimating.
Dean K Malvick: Under really similar conditions, maybe even more in some fields.
Ryan P Miller: But then, you know other fields you've seen and been in you probably seen where there's been no or maybe limited yields less so it's it's not guaranteed, I guess, and.
Dean K Malvick: No i'm not seeing anything approaching anything near that level in Minnesota those reports are from other States in areas where the disease been pretty heavy in previous years.
Dean K Malvick: And we saw fields and southeast Minnesota like a pretty severe by layton sees them, but a lot of that disease also developed later.
Dean K Malvick: late August and September after the Acropolis was pretty well alone.
Ryan P Miller: Okay, great um any other questions are coming in, here I didn't see any come through the chat or the.
Ryan P Miller: Q amp a box, but it's your carrier last chance here to ask a question, as we near the end of the program today and, as well as your Dean if you've got any final comments feel free to make those and and then we'll see if any questions come in and wrap things up here.
Angie J Peltier: i'll just ask you a question, then Dean.
Angie J Peltier: what's your you know you often see the see advertisements out saying that fungicides can improve stand ability in corn what's been your experience and.
Angie J Peltier: You know, or is there any kind of rule of thumb that you use for that I answering that sort of question.
Dean K Malvick: And that's it's it's a complicated one right there are many different things that affects tangibility i'm saying rose bought last year, where there was so much it was so much drought and other places a lot of the standard ability had nothing to do with with.
Dean K Malvick: fungal diseases and certainly the places we put fungicides on it didn't make a difference, it was it was just a drought stress.
Dean K Malvick: And decides it quite simply work best when they're controlling upon the disease there are instances where certainly they do seem to have other effects in trials process Minnesota we haven't seen a strong impact on sustainability.
Dean K Malvick: I certainly have seen some other results where they have so it's fairly highly variable.
Dean K Malvick: In the trials that that Bruce potter has tend to lead across it, and so, which he summarized in Minnesota crop needs a couple weeks ago.
Dean K Malvick: Are the odds of returning foreign were not very high, they are a little higher and higher, and so it sort of insurance application at a BT or are three stage the ladder for swimming.
Dean K Malvick: So so that's my general answer, I think the odds are that it won't provide a big benefit that there may be situations where it does.
Ryan P Miller: Good and you can always find that crap news blog it's a blog so the these newsletters don't go away if you get to aircraft news site so we're not gonna have time to put that link in here today, but I think we're at the end of the program so we're going to wrap things up.
Ryan P Miller: With things today here, I do want to call out and thank again our sponsors Minnesota research from promotion corn research and promotion console and the Minnesota so you being research and promotion console.
Ryan P Miller: As well as guests, for being on today and and helping to kind of bring this discussion along so thanks to everyone and have a good day.