Virtual Breakfast 8-8-19: Update on field crop diseases


– [Mike] Well, good morning. I’ve got seven o’clock on the iPhone, so I think it’s time to get started. I’m Mike Staton. I’m Soybean Educator with Michigan State University Extension. I’d like to welcome you to the Field Crops Virtual Breakfast. For today, the eighth of August, we have two presenters
with us this morning. We have Martin Chilvers,
our Field Crop Pathologist, and we also have Jeff Andresen,
our State Climatologist. I’m gonna go ahead and
introduce Dr. Martin Chilvers to talk about tar spot in corn. – [Martin] Good morning, everybody. So, let’s give you a bit of an update on field crop diseases. I think early today,
I just wanted to focus perhaps on tar spotting. I think it’s the most relevant
at this point in time. As I’m talking about this though, with respect to corn diseases, Northern leaf blight, gray leaf spot are a couple of other things we don’t wanna forget about in corn, and should be out there
scouting for as well. So, I’m sure quite a few of you now have seen perhaps me talk about tar spot, but just in case you haven’t, so tar spot, as the name
suggests, looks like tar’s been flecked onto the
leaves of the corn plant. And, one thing I think
that sort of distinguishes it from Northern leaf
blight and gray leaf spot is that it can look pretty innocuous, and then build to levels
that are pretty destructive, very quickly. So, it can be a little bit of a tricky one to scout for, too. You know, Northern leaf
blight and gray leaf spot are pretty easy to spot
from 10 yards away. Tar spot is not. You really gotta be up
close to those plants looking for those little lesions. And, we had a lot of
false positives at the start of the season, so people were out there
looking really closely, which is great. A lot of insect frass, so
insect poop on the leaves, looks very similar to
this tar spot in this particular photo I’m showing here, but the insect frass can be quite flat, and the one thing with insect frass is it’ll rub off the leaf pretty easily, especially with some water. It’ll tend to dissolve, so that’s one test you can do. So, any of these tar spot lesions of the tar spot fungus are really
embedded in that leaf’s tissue, and have a slight,
raised structure to them. And very often, just a very
little bit of dead tissue, or yellow tissue, just around
the tar spot lesion itself. So, last year was really the first year that we had an epidemic in Michigan, and so we had about 27 different counties with tar spot in them. The problem is, this
fungus can overwinter, so we’ve got plenty of
evidence for that now. It’s quite happy to overwinter. It overwinters on those corn leaves, so as those corn leaves do bite down, the fungus is likely to die. But, there’s enough of it there that there’s overwintering of this
fungus through that material. And, we definitely had significant losses last year in some fields, about five or six counties, where I assume you read
about 50 bushel losses. So from that, what we’re
sort of seeing here is it’s an emerging disease. It was first seen in Allegan in Michigan, and that’s certainly being worried about at the center counties here. But, now that we’ve had pretty substantial levels last year in
Macomb County and others, I fully expect that to be an issue sort of going forward. And as the season progresses, it may very well hit the
Thumb later this year. I don’t expect to yield losses this year. It seems very slow compared to
last year for the most part, but it’s starting to
pop up again this year. And again, 2018, other states surrounding Lake Michigan also
concerned tar spot looking into the season, so this
is just a cumulative map of wherever we’ve had positives over the last few years, through 2018. So, moving into this season then, we’ve got a number of counties now where we’ve got confirmations, about seven or eight counties
now with confirmations. So, those red highlights on
the counties are confirmed, the yellow is possible, and green is we’ve checked,
but we haven’t found it yet. In those situations where we’ve found it, there’s been sort of mixed results so far. So, where it’s on a plant here and there, I probably wouldn’t be too concerned at this point in time. But, where it’s on most plants, even at very, very low levels, I’d be very concerned. If it was to me, I’d be
putting a fungicide on. So, we’re in these early,
reproductive timings to help make sure that
that’s under control. And, the other thing that
we’re seeing this year again, it’s very, very slow to start, so a lot of these other states near us have also reported tar
spot, but very low levels. Except maybe under irrigation,
more close to the lake, where we’ve got more
moisture in the field. So, definitely something
to really be paying attention to right now, and perhaps making fungicide applications. And, I’ll be up in Isabella
and Gratiot later today, having to walk around and see what else we have out there. Just in terms of when it can infect, and sort of how quickly
it can cycle, I guess, here’s a photo I grabbed from last year. So, this is a volunteer corn plant at the V3 growth stage,
so a few weeks old, and that already had lesions on it. So, it looks like from the greenhouse inoculation studies we’ve done in some of the field observations, it can cycle in around
about 10 to two weeks, 10 days to two weeks, rather. So, spores are gonna land on
the plant, infect the leaf, and then, in about 10 days or thereabouts, produce those little black structures, which can release more spores. So, it’s quite capable of cycling quickly. And, here’s another example
of why I would recommend a fungicide application. So, this is out at Steph
Kerman’s place really in Oregon County, very
close to Lake Michigan. So, we were in there last year, about this time of year, August 10th, and every plant in the field
had some level of disease. But, the level of disease was really quite low for the most part. When we did ratings on the ear leaf, some ear leaves had no disease, and others had one or two spots on them. So, it was there, probably a little bit heavier
down in the lower canopy, but it was there, but not
at very high severity. Nothing we might be
particularly worried about. But from there, it really
exploded very, very quickly. So by August 24th, we were
up to about 30 or 40 tar spot lesions on a leaf, and here’s an example of that
leaf there by August 24th. And by that time, it had also reached up into the tassels, and was actually causing
lesions on the tassels. And then, we came back September seventh, and essentially the whole field was dead. So again, it’s one of those things I think that’s gonna catch us
off guard a little bit, because it is sorta, somewhat sneaky compared to Northern leaf
blight and gray leaf spot. So, here’s a couple photos, just showing you again, August 24th. By August 24th, they’re
visible from the air as well, and so that’s something
to sort of keep in mind. In terms of scouting,
you might want to think about using a drone to get up there sort of mid-August to see
where your fields are at, because I know corn is
difficult to get through. But then, there’s very
heavily infected areas they ended up watching as well, so that’s what I’m trying to show you there on the right-hand side. So last year, we sprayed
this at the R3 growth stage. August 10th, corn was a little bit more ahead of things compared
to where a lot of fields are this year. And coming back September seventh, you can see that where we
hadn’t sprayed the fungicide, things were dead. Where we had, we
preserved green leaf area. And basically, the short story of this is, use a mixed mode of action fungicide. There’s a number that was labeled, and there were a number
of other fungicides that have the Emergency Exemption label. And in terms of standability too, that fungicide really
had a pretty significant effect on standability. So, where we didn’t spray the plants, they browned down pretty heavily, and where we had, there
was still reasonable stalk integrity. Something else that we
saw last year as well, was the impact on silage. So, if we’re producing silage where we’re gonna chop this corn, we really wanna be aware of that, too. So, here’s our field shot to that grower. I think in mid to late August, the field looked frosted to him. The back end, where we had
a little bit more moisture, it’s a little bit of a
lower area of the field. So again, maybe getting up
with a drone if you have one, to have a bit of a look
to see what you can see. It might be helpful in terms
of trying to make a plan, with respect to harvest. I guess the important
thing here with harvests, in terms of silage, is perhaps getting in
there in a timely manner. So, once things really
brown down like they did here with the tar spot, our biggest problem is the moisture. And, that corn, it had dropped to 20%, so too low for silage production. So, again if we know the
disease is at the beginning, and we’re chopping those severely affected parts of the field first, just something to consider. There’s no mycotoxin
associated with this disease, unlike ear molds, where we’d also be concerned
about the mycotoxin. But, it does also affect
the quality of the feeds, so the energy content, and the indigestible contents increase. In terms of management then, so hybrid resistance is gonna be key, but I know we’ve sort of all
been caught off guard by this, because it’s such a new disease. So, we’re obviously
stuck with what we have out there this year at this point in time. So, really the important
thing at this point in time is to get out there and scout, a timely fungicide application, so if we’re aware of what’s
going on out in our fields, VT to R2, maybe R3 applications might be something to consider. And again, scouting, really being aware of what’s going on. And then, potentially being prepared to harvest early, too. So, we ran into some situations last year where we were having an issue harvesting, they’re losing grain onto the ground. So, get out, and again, check the quality of those ears, ’cause it tends to shrink the ears up. And, the grain tends to fall
out of the ears pretty easily, so something to consider. Planting into corn will
have increased the risk, so if I’m gonna go out and
scout one or two fields, then I’ll look at corn-on-corn, and certainly irrigated locations are gonna be greater risk. The rotation does not
eliminate risk of disease. We’ve had fields last year
that moldboard plowed, and they had very high levels of disease. It doesn’t mean that you’re
not gonna get disease. And irrigation, I think, was really the big thing as well last year. It was really surprising
how much that drove disease, so be very, very careful with irrigation. And so, we’d really like your help too, in just keeping track of
where this disease is at. So, we’d like to know when and
where you first see disease, and if you can pick one
or two of those fields that you can keep going back
to the rest of the season, that would be fantastic to
look at disease progression. So, just writing an estimate of the number of plants infected would be helpful, like how many out of 100, and where the disease is at on the plant. Is it lower canopy, mid, or upper? It’d be very helpful, and just some sort of
estimate of severity, and I could certainly write
some disease rating scales, if you would like that. And just a final note, we have a large field trial organized out in Allegan County
where we just sprayed, and R1 treatments went on yesterday. We did everything we
could to try and ensure that we would get disease,
but at the moment, we don’t have disease in
that particular field. I know there’s disease just
to the east of Hamilton, so it’s certainly in that county, and other fields around as well, so it should develop. So, we certainly plan to
have a field day in Allegan. Hopefully in our field trial location, we can show you tar spot, but if not, we might do that somewhere else in Allegan where we have tar spot to discuss. So, that’s gonna be September 18th, and I’m starting at about two o’clock, and just make contact. And also, if you have any questions, I’d be quite happy to take them now. – [Chris] This is Chris DiFonzo here, I would just make a comment that, Marty I don’t know how late you would be thinking of spraying
and putting fungicides on, but I think your fungicides
could be tank mixed with insecticides for
some of these ear feeding caterpillars. But, I don’t know how late
I would spray those, either. Though, once these caterpillars
are down in the ear, they’re hard to kill. But, the tank mixes would
certainly be possible. – [Martin] Yeah, that’s a
really good point, Chris. Absolutely. With respect to tar spot,
like optimal timing, we’re still trying to figure that out. Definitely, reproductive
stages are gonna be far more beneficial than
the early vegetative stages, unless for some reason
there’s really high levels in that early vegetative point. So, absolutely tank mixing,
when it’s appropriate, could be a very smart thing to do. So, we went up to R3 last season, we’d have to double check labels to see how late we can go with that. And obviously, if you’re
coming in really late. And again, you wanna be careful thinking about these as rescue treatments, right? If you’ve got very, very
high levels of disease, you’re not necessarily
gonna shut that down, right? So, we wanna be proactive
against scouting on what’s there, and trying to make that
application probably between R1 and R3. Again, double checking that label. – [Chris] Yeah, and also
scouting for what insects are there, and if they’re actually there. And like I said, I think
for a lot of these fields, it would be too late anyway
for the insecticides, but just wanted to mention that. – [Martin] For sure. – [Mike] Marty, I don’t see any more questions in the chat box. If you do have some for Marty though, please go ahead and
continue to type them in, and we will get those addressed. On your screen right now, you’re gonna see that MSU’s reminder that we have some really
solid resources available to help with the delayed
planting challenges that we face this year, and all the problems that those are continuing to create for, or potentially create for
producers across the state. So, this website is a
compilation of those resources. It’s a growing resource
that’s gonna be available, so please check that out. We also have this. We wanna thank you for attending. This is a good way for us to
get information out to you, so we really appreciate that. And then finally, there is a survey, and we would appreciate it
if you would fill this out. There, you see the link on the screen. The link has also been
typed into the chat box. So, please help us out by
filling that survey out.

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