8 - 2020 South Central Ag Lab Field Day
2020 South Central Ag Lab Field Day
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- [00:00:04.910]My name is Tamra Jackson Ziems,
Nebraska Extension plant pathologist,
- [00:00:09.080]covering diseases of
corn and grain sorghum.
- [00:00:11.990]Today we're at the South
Central Ag Lab in Clay County.
- [00:00:14.810]And I want to talk to
you about Southern Rust.
- [00:00:17.750]We're mid August right now in Southern
Rust has been an issue for us in various
- [00:00:21.860]parts of the state all the
way to the Northern regions,
- [00:00:24.590]but it really started down here in the
Southern counties where we see it more
- [00:00:28.910]routinely. This year is worse
in many of these fields.
- [00:00:32.840]We're beginning to get severe Southern
rust where it's more widespread in
- [00:00:37.070]fields. Many of them of
course have also been treated.
- [00:00:40.610]And so when you're out there
looking at Southern Rust, of course,
- [00:00:43.520]this is a rust disease that produces
a lot of orange and tan spores.
- [00:00:48.470]Those spores are primarily
on the top side of the leaf.
- [00:00:51.800]And so you can see them here on
this leaf that I've got in my hand.
- [00:00:56.000]And so these spores do
rub off on your fingers.
- [00:00:59.300]And so you can see that orange
discoloration there uniquely,
- [00:01:04.280]we don't generally see Southern Rust
sportive element on the backside of the
- [00:01:08.570]leaf. And so that's one way we use it to
help differentiate it from other rust,
- [00:01:13.940]unless you see it near the mid ribs.
Sometimes we see spore development there,
- [00:01:18.020]or in the case of this year in 2020,
- [00:01:20.750]where we've had a lot of wind
damage and green snapping,
- [00:01:24.320]where a lot of leaves have
been flipped upside down.
- [00:01:26.690]Suddenly the bottom of the leaf is the
top side and that's where we've been
- [00:01:30.020]seeing sporulation of course,
- [00:01:32.420]many of our fungicides do a
good job managing Southern Rust.
- [00:01:36.290]And so timing is critical here.
- [00:01:38.960]And many fungicides only
give us about 21 days of
- [00:01:44.690]And so applying it too early might mean
if we have a late bout with Southern
- [00:01:49.670]that's when we see the
fungicide protection come to
an end and we see Southern
- [00:01:54.620]rust development,
- [00:01:55.610]and we come to questions about whether
or not we should treat this late in the
- [00:01:59.510]season, late dough and getting
into dent like we are now,
- [00:02:03.770]we have a very slim chance of getting
a return on the investment of a foliar
- [00:02:07.760]fungicide. And so we have to
think really hard about that.
- [00:02:11.720]Some fields may be especially vulnerable.
- [00:02:14.330]And so anything that's very late planted
that still early in its development
- [00:02:19.070]say in the milk stager early DOUGH
may still benefit from some of those
- [00:02:24.590]And so you really have to get out in
the field and look for Southern Rust
- [00:02:28.580]because it is very patchy in the
field and various throughout,
- [00:02:32.510]toward the end of the season, we'll
see this disease continue to spread,
- [00:02:36.140]especially we're seeing it
now in the lower canopy,
- [00:02:39.020]a weather conditions are favorable and
it's warmer and human wholesale in the
- [00:02:43.310]upper canopy too. I
want to warn everybody.
- [00:02:46.250]If you had a lot of Southern
rust or any other disease,
- [00:02:49.880]it might mean that standability
could be impacted before harvest.
- [00:02:53.960]And so it would be worth your time
to spend time out in the field after
- [00:02:59.740]checking on standability and stock
strength by pushing on those plants
- [00:03:04.900]and keeping track of the number
that lodge is below the ear leaf,
- [00:03:09.280]it would help you identify
which fields may have a problem.
- [00:03:12.550]You'd need to do that to at
least a hundred plants or
so in each field to get an
- [00:03:16.810]idea which ones are Mo more
vulnerable. The lodging.
- [00:03:20.080]We often have high wind events late
in the season prior to harvest,
- [00:03:23.950]and that could put some of those
fields at risk for harvest problems.
- [00:03:28.180]Later on next, I want to
talk about gray leaf spot,
- [00:03:32.020]and that's what I'm holding here,
where the rectangular lesions are.
- [00:03:35.500]And you would have seen Gabby talk about
that compared to what those lesions
- [00:03:39.850]look like compared to
bacterial leaf streak. Well,
- [00:03:43.180]green leaf spot is the disease that
we normally see more commonly in South
- [00:03:47.290]central Nebraska, but this
year that hasn't been the case.
- [00:03:50.380]We've had much less gray leaf
spot, mainly in the lower canopy.
- [00:03:54.370]And it just has not become severe.
- [00:03:56.560]Like we would normally see this time
of year warm weather conditions.
- [00:04:00.190]High humidity could drive that to become
worse as we get closer to the end of
- [00:04:04.540]the season. And so continue
to look for resistant hybrids.
- [00:04:09.010]And of course, foliar
fungicides, if they're needed,
- [00:04:11.620]can also manage that disease.
- [00:04:14.140]The leaf I'm holding right now
has Pfizer Derma Brown spot,
- [00:04:17.860]the fungus causing this disease creates
lesions that look very different,
- [00:04:22.630]whether you're talking about the leaf
blade or in the Mo in the mid rib,
- [00:04:26.710]like we're looking at
here on the leaf blade,
- [00:04:29.710]it can be yellow to orange in color.
- [00:04:31.690]And some people mistake it for
even Southern Rust in the midrib.
- [00:04:36.280]You see that it's very
dark purple or even black.
- [00:04:39.130]And sometimes we see those
small dots, even on leaf sheets.
- [00:04:43.360]This disease has not
been as common this year.
- [00:04:46.570]This is one that was much more common
last year because of how bad the wind or
- [00:04:50.590]excuse me, how much rainfall we had.
- [00:04:53.530]The timing of that
rainfall is critical too.
- [00:04:56.350]And although if you have a susceptible
hybrid with a lot of leaf area covered,
- [00:05:00.520]it can cost you yield.
- [00:05:02.470]The thing that I think people are
beginning to mistake this disease for is
- [00:05:06.250]another disease that I want to make
sure that you're watching for later this
- [00:05:09.760]fall, that disease is called tar spot.
- [00:05:12.850]And you may have already heard about
it in the corn belt East of us,
- [00:05:16.330]especially over into Iowa.
- [00:05:18.970]We know that tar spot is
in Western Iowa so far.
- [00:05:23.500]It has not been confirmed in Nebraska,
- [00:05:25.570]but we expect that that disease
will eventually move into our state.
- [00:05:29.110]And I hope that people, especially
in the Eastern most counties,
- [00:05:32.950]we'll scout fields and watch for
plants that have tiny black dots on
- [00:05:37.450]leaps. Those tiny black dots are
fungal reproductive structures.
- [00:05:42.040]They produce spores that help
the disease spread it's favored,
- [00:05:45.970]especially by cooler
conditions, wet conditions.
- [00:05:49.210]And it can be when born and splashed
around this is a disease we need to watch
- [00:05:54.010]for. It can be devastating,
the yield in severe cases.
- [00:05:58.130]And they've seen up to 50% yield
loss in some of the Eastern corn
- [00:06:02.840]belt, not something that we think we'll
see here, at least not anytime soon,
- [00:06:08.120]but in States like Michigan, where
they have a lot of irrigation,
- [00:06:11.450]it has aggravated this
disease and increased it.
- [00:06:14.840]That's why we need to watch
carefully for this disease.
- [00:06:18.020]The fungus will over winter and it'll
develop year after year in that same
- [00:06:23.120]And so we want to let producers know when
it moves in so that we can monitor for
- [00:06:27.140]it. And eventually if
fungicides are needed,
- [00:06:29.870]we'll know when and where
to spray additional diseases
and things that you may
- [00:06:34.520]confuse with tar spot as this
Southern Rust matures out here,
- [00:06:38.420]the spores will eventually be black,
- [00:06:40.940]the fungus switches to black
spores and trying to overwinter.
- [00:06:44.810]And it's easy to confuse those
with tar spot. In addition,
- [00:06:48.800]I want to let you know too,
- [00:06:49.820]the most common thing you're going to
see that causes black dots is insect
- [00:06:52.970]frass. And so make sure you try to rub
it off. And if you can't rub it off,
- [00:06:57.200]there's a chance that it could
be the fungus causing tar spot.
- [00:07:00.530]And please contact us in
Nebraska Extension and get
us a sample to the plant and
- [00:07:04.130]pest diagnostic clinic. We've
moved over to the soybeans now,
- [00:07:08.120]and I want to talk to you about a few
important diseases that we're beginning to
- [00:07:11.180]see on soybean. The first one is sudden
death syndrome or what we call SDS.
- [00:07:16.070]And that's beginning to flare up in some
of the fields in South central Nebraska
- [00:07:21.020]And so the things that you'll notice
first is that the upper leaves of these
- [00:07:25.100]soybean plants are beginning to turn
yellow. And when you look closer,
- [00:07:29.540]you'll notice that the yellowing is
especially between the leaf veins.
- [00:07:34.640]Eventually that area will
turn necrotic or Brown,
- [00:07:38.780]and the entire leaves will
die and eventually fall off
and defoliate that plant.
- [00:07:43.610]In fact, that can happen
within a couple of weeks.
- [00:07:45.770]That's why they call it
sudden death syndrome,
- [00:07:48.260]the same plants that have the leaf
symptoms also have severely rotted
- [00:07:52.940]roots. And so you'll find when you
go down and try to pull those up,
- [00:07:56.810]they probably are going to pull pretty
easily because many of the lateral roots
- [00:08:00.230]have rotted off. Sometimes
if you look very closely,
- [00:08:04.250]you may see a bright blue
discoloration. If you do,
- [00:08:08.750]that's almost a guarantee that what you
have is SDS because the fungus causing
- [00:08:12.920]that disease, sporulate
bright cobalt blue.
- [00:08:16.280]And sometimes we'll see that
on the surface of roots,
- [00:08:19.700]a few things that you
need to know about SDS.
- [00:08:22.940]We do have good resistance
to that disease,
- [00:08:25.430]and that is your number one
way to manage it. In fact,
- [00:08:28.490]we've seen an increase of 80%
yield in the presence of SDS.
- [00:08:32.960]When you select resistant
varieties. In addition,
- [00:08:36.350]we also have a seed treatment Allevo
that has been effective against sudden
- [00:08:40.700]death syndrome.
- [00:08:41.990]And it's given us benefits
of 20% increases in yield.
- [00:08:46.790]So we recommend in severe cases,
- [00:08:49.040]you can use that seed treatment product
on top of selecting a resistant variety.
- [00:08:54.440]In addition, when we talk about SDS,
- [00:08:56.490]I want to make sure that you understand
that soybean cyst nematode is
- [00:09:01.350]important because it can impact
sudden death syndrome development,
- [00:09:05.070]making it developed both
earlier and become more severe
than if the nematode was
- [00:09:09.420]not there.
- [00:09:10.920]Nematode distribution across Nebraska
is becoming increasingly widespread.
- [00:09:15.870]It's important that you sample and know
whether that nematode is in your field.
- [00:09:20.220]We know soybean cyst nematode
can cost up to 30% yield loss
- [00:09:25.140]with no visible or measurable symptoms
other than you'll loss itself.
- [00:09:30.480]And so it's critical that we know where
it's at and that we monitor the eggs per
- [00:09:35.130]a hundred CCS of soil as a
measure of how bad that's getting.
- [00:09:40.020]The good news is soybean cyst can be
managed with crop rotation to a non host
- [00:09:44.820]crop, especially corn,
or even with alfalfa.
- [00:09:48.750]And although we do have resistant
varieties for soybean cyst nematode,
- [00:09:53.280]and it's important that we select those,
- [00:09:56.130]remember that the nematode can
adapt to the resistant variety.
- [00:10:00.660]And the unfortunate part is that we are
using most of our resistant varieties
- [00:10:05.430]coming from the same line
that's PI 88, seven 88.
- [00:10:10.530]Now we know in many
States, even in Nebraska,
- [00:10:13.710]that nematodes are adapting
to that level of resistance.
- [00:10:17.220]In some States that resistance is
no longer useful in Nebraska here.
- [00:10:21.960]We know that at least 50% of our nematode
populations can reproduce on that
- [00:10:26.460]level of resistance on
that type of resistance.
- [00:10:29.430]It's important when you
select your varieties that
not only are you looking for
- [00:10:34.320]resistant varieties,
- [00:10:35.550]but you're also changing varieties
because the nematode can adapt not just to
- [00:10:39.750]the resistance, but also
to the variety itself.
- [00:10:42.960]And so be sure and keep
those things in mind,
- [00:10:46.170]as well as you have seed treatment and
a mat asides that you can also use.
- [00:10:50.850]And using a.
- [00:10:52.500]An assortment of different combinations
of these strategies will help give you
- [00:10:56.790]the most favorable results
against soybean cyst nematode.
- [00:11:00.780]And if you're not sure
if you have soybean cyst,
- [00:11:03.090]but you're having a hard time
meeting your, your yield goals,
- [00:11:07.350]this could be something
that's holding you back.
- [00:11:09.780]You can sample in any crop any time
of year down to about eight inches
- [00:11:15.300]and that can be processed for
soybean cyst nematode to summarize.
- [00:11:19.980]We've talked about a number of diseases
today in both corn and soybean,
- [00:11:24.270]and it's important that you review what
your fields have and keep track of that
- [00:11:28.530]because that'll help you
make wise decisions this
winter on which varieties to
- [00:11:33.480]select and better position in those
fields. When you come back to soybeans,
- [00:11:38.040]there's other diseases, of course,
- [00:11:39.390]that you should keep your eyes out
on including this time of year,
- [00:11:42.270]like frogeye leaf spot.
- [00:11:43.860]So I encourage you to please go
to graduate student Asha Monte's
- [00:11:48.510]presentation on frogeye and learn more
about how we've learned that we have
- [00:11:52.710]fungicide in Nebraska and how that's
going to change your management
- [00:11:57.400]strategies for that disease.
- [00:11:59.560]If you need help identifying or
managing any of these diseases,
- [00:12:04.030]please send a sample to the UNL
plantain pest diagnostic clinic,
- [00:12:07.690]or contact us in Nebraska
Extension for more information,
- [00:12:10.900]thank you for joining us.
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