- So first we have Daren Mueller.
He's an assistant professor
and extension plant pathologist at Iowa State.
Darren's responsibilities include
the management of soybean diseases.
He is originally from Clinton, Wisconsin,
and he earned his bachelor's degree
in meat and animal science at the UW of Madison,
and his master's and PhD in plant pathology
from the University of Illinois.
So, welcome, Daren.
(audience applause)
- Thanks for the introduction.
All right, so this talk is called
Integrated Management of Sudden Death Syndrome on Soybean,
and as an extension person I usually sort of,
you know, encourage questions and interruptions,
but because this is being videotaped
I'll hold the questions until the end,
so if you have any questions or something's not clear,
please bring it up at the end.
All right, so sudden death syndrome is probably not
the number one disease in Wisconsin,
but it's certainly one of the diseases that you guys
are going to see sort of on the rise.
It's one that, in Iowa, we first saw in 1993,
and since that time it has really established itself
as probably the number one disease,
if not number two behind soybean cyst nematode,
so it's been a fairly important disease in Iowa,
especially in pockets of Iowa.
The symptoms are going to be sort of
the classic symptoms you see in any of the publications,
that yellowing or death between the veins,
and you usually see it in patches, usually the leaves.
If the disease progresses the leaves will drop off
and you'll still see petioles on that plant.
However, it's a little bit of a misnomer,
the sudden death syndrome name's a little bit of a misnomer,
because actually the disease starts
right away in the season.
And so the plant's actually infected
probably all season long,
you just don't see the foliar symptoms until later.
And so the first phase of the disease is the root rot phase,
and so the picture on your right hand side,
that plant on the right hand side of that picture,
it shows a really good depiction
of what root rot looks like.
And so this is caused by a pathogen
called Fusarium virguliforme.
The Fusarium pathogens in general,
we call them root nibblers.
Which means that they're going to be
attacking the lateral roots,
they're sure going to be reducing that root size
sort of overall.
And so you can see that this brown is rotted,
it's a little bit smaller,
that's sort of what that root rot phase looks like.
Later in the season, you could be splitting the stems.
In Iowa you have actually,
you're sort of blessed or cursed with other diseases
that look like sudden death syndrome.
You have brown stem rot,
you have some stem cankers that will cause
fairly similar foliar diseases.
White mold will cause that foliar symptom,
at least briefly, if you get out there at the wrong time.
Or the right time.
And so it's really important for sudden death syndrome
to actually slow down your vehicle enough
to get out of it safely,
and then wander into the field and pull a few plants
and split that stem and look at it.
So the picture on your left hand side,
that's sort of the browning in the vascular tissue,
it's not in the pith like you'd see with brown stem rot.
And so that's usually something you can see
with a pathogen or disease caused by Fusarium.
You can also pull plants up at the end of the year,
unless you're a weight lifter,
the fact that that plant easily pulls out of the ground
is evidence that it might be sudden death syndrome,
because the root, again, there's a root rot phase,
brown stem rot's not going to have that,
it's going to be a bit tougher to pull up
some of the plants that have a healthier root system,
it'll be tougher to pull those plants up.
If it pulls up easily,
sometimes you can see that blueish growth
on the outside of the plant.
This doesn't happen all the time,
but if you do see it that's a sign
that this is sudden death syndrome.
All right, so in this talk there's gonna be several slides
that use the term "disease index".
This is just a dorky plant pathology term
that we use to combine incidence,
the number of plants or the percentage of plants
that are infected,
and severity, sort of how sad those plants are, so.
And then we put it on a scale of 0-100,
so 100 being every single plant is extremely sad or dead,
and zero being everything is alive.
And then to put it into perspective,
what does a DX of 10 mean?
Usually on average that equals about a 7% yield reduction
when you're looking at sudden death syndrome.
All right, so for management of SDS,
it really starts with resistant varieties.
And I'm not going to go over resistant varieties,
except to tell you that that's usually where you start.
So if you have a field that has a history of SDS,
the encouragement is to select a variety
that is resistant to SDS,
and the other thing is
to start sort of an indicator disease.
I've seen there's a couple of other
indicator diseases out there that you might actually have
a soybean cyst nematode problem as well.
Usually when you have soybean cyst nematode,
SDS is a little bit worse in those fields,
or it might show up a little bit earlier.
So if you do start seeing SDS,
go out and soil sample and check your SCM levels
and manage SCM using resistant varieties as well.
So that's sort of the resistance side of things.
So we are going to focus on seed treatments.
This is a study that was done at Iowa State University
where we drew plants at two different ages,
and then we added inoculum.
So we had the inoculum in that little fake beaker up there
and we poured it into each of those pots
once the plants get a different age,
and then we waited 18 or 38 days
and looked at the root rot and the foliar symptoms.
What we found when we inoculated right at planting,
the root rot phase, we almost had 100% severity
in that root rot phase.
And then if you look at all the other plants,
and that's day four to day 35,
the root rot was hovering right around the 50%
of the roots being rotted.
If you look at the foliar symptoms,
you had a lot of disease at day zero,
when it was inoculated at day zero,
and absolutely no foliar symptoms for all the other ones.
And so usually at this point I try to challenge people
as to think about why that would be.
There's too many people in the room,
so I'm gonna just hop right to the punchline.
And so if you start looking
at the cross-section of the root,
this is always the encouragement
to actually pay attention in biology
or to try to convince your kids or grandkids
to pay attention in biology class,
'cause this stuff might come back and haunt you later.
But this is the cross-section or the anatomy of a root,
and if you look at the outside, you have the epidermis,
sort of the big bulk of it is the cortex,
and there's the endodermis that is protecting
the vascular tissue, which is in the center.
And so if you saw Fusarium virguliforme,
the pathogen that causes SDS, inside the cortex,
you would just have root rot.
If that Fusarium virguliforme got past the endodermis
into the vascular tissue,
that is where you could also have root rot
plus the second phase of the disease.
So what happens is the pathogen stays in the roots
and never really leaves the roots all season long,
even when you see the foliar symptoms,
it produces a toxin,
a toxin gets translocated to the top
and that's what causes the foliar symptoms.
And so if that pathogen stays in the cortex
and it doesn't get into the vascular tissue,
then it's sort of hanging out there in the roots
and causing root rot.
And so...
This pathogen, although it causes a lot of damage,
it's not really that aggressive of a pathogen
as far as being able to grow internally.
So a lot of times if that endodermis is a couple of days old
or it's hardened off,
it'll hit that endodermis
and it won't try to grow through it.
And so that root age,
and starting looking at that root structure,
is really a critical thing.
That long story is saying, seed treatment should work.
And so the encouragement,
one of the things that's sort of like
at the biology of this pathosystem,
is that seed treatments should do a pretty darn good job
as far as managing this.
If you rewind about three or four years ago
and start looking at all the commercially available products
that were out there for anybody that is a graduate student
or has written a thesis,
this is always a really depressing slide
because this is an entire thesis summarized on one slide,
and really the entire thing can be summarized
in one bullet point, and that's that nothing worked.
(audience laughter)
And so you sort of have to stomach that,
that might be a sort of a roll of the dice
as far as the graduate students out there.
But really, everything we evaluated,
and we looked at a lot of different things.
We looked at the quantitative PCR,
looking at the amount of DNA in the roots.
We looked at scanning every root and starting to see
if there's any differences in the root structure.
And really, everything came back as,
every commercially available product three or four years ago
came back as not effective.
So fast forward to 2013, we started evaluating a product
from Bayer CropScience called ILeVO.
In 2015, another product called Mertect from Syngenta
became available that at least has SDS on its label.
There are other products out there
that are sort of less common,
one's called HeadsUp that also has SDS
in the literature as far as it being effective.
And so we had sort of a collective group of people
from all of the states that are being mentioned on the slide
started evaluating these two treatments,
and I have data from each of these states,
so that's going to be shown over the next couple of slides.
So this first one is in 2015 alone,
this is the first year we were able to
evaluate things side by side,
so this is looking at ILeVO, Mertect, and HeadsUp
on both resistant and susceptible varieties
at seven locations, two of them in Iowa,
two in Ontario, Canada,
then one in Illinois, Indiana, and Michigan.
And each of these products are being
compared to a base seed treatment.
So ILeVO plus Poncho/VotiVO is being compared to
that same group of products,
or just Evergol Energy, et cetera,
and then the Mertect is being compared to the Syngenta base
and then the HeadsUp is being compared to
the Bayer base seed treatment.
So if you look at the bars,
each bar is going to be representing 14 data points
again, seven locations, two varieties at each location.
And the black bar is the percentage of
disease reduction.
And so you can see that the bigger the bar,
the more disease has been reduced.
And the red bar is the yield response, and so
for ILeVO, the yield response was just under four bushels,
it was 3.8 across these seven locations,
and the reduction in disease was
just a little bit more than five DX.
And then you look at Mertect and HeadsUp,
we're hovering right around zero for both of these
on average across the seven locations.
So...
I'm gonna just focus the rest of it,
or the next couple slides, just on ILeVO alone.
And so this is sort of where all the other states
are coming in around that list.
If you look at 2013, we had 60 observations total,
2014, 194 and then 2015, 210 observations.
So the first cluster of graphs is the average disease,
and so in 2013 we had just under 10 DX on average.
In 2014 we had over 20 DX,
and then in 2015 it fell in between those two years.
For SDS reduction, on average, you're looking at,
again, it's sort of flat,
it's right around that 5 DX reduction
when you're averaging it across all of the observations.
And then for the last one, the yield response,
it really matches the amount of disease,
and so 2013 had a yield response
on average of about two and a half,
2014 on average about five,
and then 2015, that fell in between those two years.
So to break that down in a couple of different ways,
if you look at the resistant versus susceptible varieties,
and this would be my encouragement
to anyone in the seed industry, is that there's not a lot
of really good sources of resistance to SDS
that are out there.
It's improving each year.
And my encouragement as people are selecting varieties,
if you have a field with SDS,
is to continue to try to find
the best variety that's out there
but there is not a big difference.
And so when we're looking at
susceptible versus moderately resistant
or moderately susceptible line,
you know, on that scale of one to nine,
you're looking at something between a four and a five,
or a five and a six.
And so there's not a big difference there,
and that sort of is reflected here.
There's not a huge difference
when you start looking at resistant versus susceptible.
But we do see a little bit more of a yield response
when we have a variety that is labeled as susceptible.
So the average yield response
is a 4.2 when you have susceptible,
and it's about a 3.2 when you have a moderate
or some kind of level of resistance that's in there.
Really, the biggest breakout is going to be
looking at the levels of disease.
And coming from a plant pathologist,
this shouldn't be a big surprise, but if you have -
there's a couple of things to point out on this slide.
The first one is, if you have absolutely no disease,
no foliar disease showing up,
there's still 53 observations that we had with this scenario
and we still had a 1.6 bushel yield response.
And so in the seed treatment world,
that's really not that bad.
So the question would be, well, what's going on there?
And so there's a couple of different thoughts.
The first one would be, there's just maybe,
the disease is hanging out in the cortex
and you just have the root rot phase,
and so maybe there's some of the yield differences
are looking at that root rot phase of the disease.
The second one is, sort of the reason they found this,
Bayer found this as an SDS seed treatment,
is that it has nematicide properties.
And so maybe there's something going on in that root system
looking at the nematodes.
And we really don't know,
we have a graduate student that's looking at that,
that's sort of some of the research that's going on
is trying to piece apart
what's going on in that root system.
So the next phase is sort of that zero to ten,
and I have it brokered out in two different categories,
but really if you have a disease index of zero to ten,
you're looking at yield responses in the 3.3 to 3.7,
and just to put things in perspective,
on that scale, that one to nine scale
that we use for severity,
we usually do not start seeing defoliation
until you get into the twenties and 25-30, and so
this is still fairly low levels of disease.
Now, it's noticeable, you can see it, it's not bad,
but we're not talking about patches of disease
where you're walking out there,
that's sort of catastrophic and dropping leaves everywhere.
So still fairly low levels, and you'll see that
the yield response is around three and a half,
and then you get a DX over 10,
you can see that yield response
goes up almost five and a half.
So the other thing to point out is that
this is something that we keep seeing,
that there is sort of an upper limit to ILeVO.
So if you look at the last two categories,
the total disease or the average disease
is 14.8 in that 10-20,
and then your reduction was about 50%,
so it dropped it down to 7.9,
but then if you get into that last one
where the average DX was 47 and a half,
there's not a 50% reduction in disease.
So you're looking at, you know, there's sort of an upper limit.
As you start to see more disease pressure,
you do see disease,
you're still going to see disease out there with ILeVO,
and you can see that the yield response,
there's a big difference
in the amount of disease that's there,
and that yield response sort of plateaus at that point.
All right, so that's all the good news about ILeVO.
There is the dark side of ILeVO,
and this is it does cause a lot of damage early in the season.
So for anyone that is planting ILeVO,
or ILeVO-treated seed, this is something to keep an eye on.
In 2015 we saw more damage than we had seen
in all the previous years that we evaluated it.
And all of the people that looked at it for the first time,
at least in Iowa, definitely noticed it,
because my phone didn't stop ringing for about three weeks.
So Bayer calls it a halo effect.
I tend to just stick with phytotoxicity
because if you look at that picture on your left hand side
or on your right hand side,
that's not a halo effect.
And so this is really a lot more than just a halo.
So if you get out there
at the right growth stage to see this,
you can see the entire field sort of looking brown
and sort of having a pretty bad look
or a cast to that field.
And so sort of keep that in mind, but
I would say it was really good
to see a lot of people going out and looking,
because as a plant pathologist there are other things
that can cause early season damage,
and it's good, sort of an awareness, it's good to see it.
I actually got more reports
of pythium seedling blight this year
than I had previously gotten as well,
because people were out looking,
and this can cause very similar symptoms
or very similar damage.
There are also several different herbicides
that can cause this as well,
and really when it becomes interesting is
when you have a field that has
maybe a little bit of pythium,
somebody has applied
a soil-applied or pre-emerge herbicide,
and you have ILeVO-treated seed.
And then you have to start sorting out
what's causing what in this situation.
So in 2014 and 2015, we did a study
where we're looking at the interactions
between the pre-emerge herbicides and ILeVO-treated seed.
This was done in Indiana with Kiersten Wise
and Iowa, by myself,
and then we had a resistant and susceptible variety
at each location
and each one of these was treated or not treated
with ILeVO,
and then we tested several common pre-emerge herbicides.
And we looked at phytotoxicity, at V1 and V4,
and then stand at V4,
and really what we found was that
there was damage caused by the seed treatment,
there was damage caused by the pre-emerge herbicide,
but there was no interaction.
Meaning that if you had a scale of one to ten,
and damage was a two with the seed treatment
and a two with the herbicide,
it didn't add up to eight. It added up to four.
And so there was no real interaction.
And just like all the other studies, the ILeVO,
there was no lasting effect on stand,
there was a positive effect with the herbicides.
Or what with as far as reducing disease
and increase in yield.
All right, to summarize, seed treatments,
ILeVO does work,
it worked better than the other products we evaluated.
Yield responses were slightly higher
in a susceptible variety
and definitely higher when you had disease index above 10.
All right, then the last point I have is,
as far as sort of an integrated management of SDS
is looking at cultural practices,
and I'm only going to look at one,
I'm going to pick on Iowa farmers
because we did an evaluation,
we did a survey and we asked them,
and 96% came back and said
they rotate to manage SDS in their state,
and you can probably guess what the rotation is in Iowa,
it's going to be corn.
And so there's a problem with that.
Because if you rotate the corn, it doesn't work.
And we have a study where we're looking at
the amount of times we can get
Fusarium virguliforme isolated from different residues,
and you can see that sort of
the higher the bar the happier it is,
in that different plant part,
and the first two columns you have there,
the corn residue was,
you could isolate Fusarium virguliforme from that
as frequent as you could from the soybeans.
And to sort of give you an idea of some perspective on that,
this is a field study that was done,
started about 15 years ago in Iowa
and we've been evaluating it for the last six years,
and this is in 2010.
The picture on your right is where
you have a lot of SDS in that two-year rotation
and not in the three-year rotation.
And so the three-year rotation includes oats and red clover,
the four-year rotation has oats and alfalfa,
and if you look at over time,
the amount of SDS that's shown up in that field
where we have SDS showing up
is less disease in the three-year rotation
and even less disease in the four-year rotation.
So why is that?
We've been studying the heck out of these plots,
trying to figure out what's going on in there,
and it really comes down to the amount of inoculum
and it comes down to the amount of years
that corn is present, and the more corn,
the more inoculum you're going to have out there,
the more SDS you're going to have when it comes to soybeans.
So with that, a big thanks to all the people
that contributed data to this presentation,
also the checkoff for their funding,
and also Bayer CropScience, so.
With that,
okay.
(audience applause)