Narrator: The following presentation
is part of the Agronomy and Horticulture Seminar Series
at the University of Nebraska, Lincoln.
-: Good afternoon, everybody.
My name is Steve Knezevic.
I'm the weed scientist with UNL.
I've been here about 25 years almost,
and it is my pleasure to welcome Dr. Anita Dille.
She's coming from a K-State, which is a great school.
I did my PhD there, so I can testify to that.
Anyway, Anita has an interesting background.
She grew up in Canada.
She was born in Netherlands, in Holland,
but when she was only about a year old,
her family moved to Canada.
And then she and I crossed paths many times.
In fact, we did our Master's degree together
at the University of Guelph with Clarence Swanton there.
Anyway, so we've known each other, should we say how long?
Almost 30 years.
And then from University of Guelph
she came to Nebraska to do her PhD with Dave Mortenson.
That was,
pretty active with the Weed Science Society,
and we've done a lot of projects over there.
And then today she's gonna talk about cover crops.
So, the floor is yours, Anita.
-: Thank you very much, Steve.
And thanks, everyone, for being here.
His introduction was tamer than I thought, so that was good.
But I'm excited to be back here
because we have known each other for so long.
And so we have worked together
on a number of different projects.
Crisscrossed paths,
gone to the same kind of places to do presentations.
So, again, just a little bit about my path.
So I did grow up in Ontario, close to Ridgetown,
which is a sub-campus of the University of Guelph.
So my parents still farm here,
just right on the north shore of Lake Erie.
Went to Guelph, did my undergrad and my Master's there,
crop science and then a weed science Master's.
So this is my parents' farm from the sort of backside,
looking at the soybean field.
I ended up then in Nebraska at Lincoln,
and I just drove two and a half hours south
when I started my position at K-State,
in the Agronomy Department there in weed science.
I met my husband there,
so we ended up purchasing some farm ground as well.
So we do a little farming on the side,
as well as both of us working for the Agronomy Department.
And so come the 4th of July, 1st of July,
I get to fly both of my flags on our front porch
to celebrate our nationalities there.
But I've really enjoyed being in Kansas,
and the kinds of things that I do there
since I was hired to about 2018,
my position was 50-50 research and teaching.
And so I do our undergraduate weed science instruction
as well as a second integrated weed management course
as part of our agronomy curriculum.
And then my research area has been more in weed ecology.
So thinking about the biology of the weed species,
how do they interact in their environment?
And then cover really has popped up as a real big interest
already for me, starting in about 2007.
So we've been working on it for 12, 13 years,
when we have different systems that we're interested in.
So this just highlights
some groups of our students out looking for weeds
or looking at the sprayer
or planning how to go out to a field
and do some weed scouting.
Every once in a while,
I get a chance to do sort of an
extension kind of outreach presentation as well.
So that was that particular one.
And then been involved in our professional society.
So I've served in the North Central Weed Science Society
at the regional level and currently with
the National Weed Science Society of America.
And one of our projects that we've done there
is report on yield losses in crops across
several different crops across the country.
And so that's been a lot of fun,
trying to summarize just the real impact weeds have.
And so we know that that's just a real important component
of thinking about management.
So, showing off a little bit of my purple.
Our students, of course, are wearing purple,
and henbit, of course, is a great purple weed
to be out looking at it in the spring.
So that's what we're doing.
So since, we did some work in 2007,
but then in the early
2012, 2013,
all of a sudden the farmers
were really asking for information on this.
We were starting to see, of course,
the increase of glyphosate-resistant weeds.
That system was not gonna work for us anymore.
How do I do some alternative kind of practices
to mitigate that?
And we also had areas where farmers were starting to
introduce more of the soil applied herbicides.
Atrazine was a big product.
That was an issue in some of these watersheds
where it was gonna run off into their reservoir
that's used for city water, for example, in Wichita.
So all of a sudden it's like
who on campus is talking about cover crops?
And basically I said, well, I've done a little bit,
but I can talk a lot about cover crops if you wanted me to.
So that's really where we got started,
out visiting with farmers and asking them questions
and trying to figure out
how to fit cover crops into their system.
And so when we think about it, probably similar to Nebraska,
our systems are very diverse
as we move from east to west across the state.
And so we look at, you know,
what kind of cropping system do they have
starting on the far west side with a winter wheat fallow,
long fallow periods.
The fallow was very heavily herbicide-based weed management.
And we were just seeing, you know, lots of problem weeds.
How do I do something different in that environment?
Adding another crop, grain sorghum for us.
We're the number one state in Kansas
to produce grain sorghum.
So we see just a tremendous area
in those low rainfall environments.
As I get more rainfall, I can switch to a corn,
I can introduce a soybean into that system.
And then as we get to the southeast corner of the state,
we have enough moisture that there are corn, winter wheat,
double crop, soybean, that's a very tight kind of rotations.
We've got challenges in all of those systems
for weed management.
Where do I fit a cover crop in there?
Does it fit in that fallow period, like here?
Or how do I squish it in there
if that's something that I want to do?
So those are some of the topics that I'll share with you.
So this is our rainfall gradient across Kansas.
Well, Manhattan is located here,
but we've got over 40 inches in the southeast corner.
And with each about 70 miles,
we just lose an inch as we go across,
so we're down to the 10 to 14 inches on the west
as we look at that.
And of course, a lot of this is irrigated production
with the Ogallala aquifer
and using that for heavy corn production.
But again, running out of water,
so how do we introduce different cropping systems in there
to manage that and the weeds that we're dealing with?
So my overview today
of some of the things I'm thinking about.
So some of this is research
based on what students have been doing in the program,
as well as when I'm out giving extension talks.
What kind of things am I hearing
and learning from our folks?
So what is always my first question as a weed ecologist
is what weed are you worried about?
Because we need to understand its biology and where it,
what the issue is,
and then move to thinking about
how do I fit that in my crop rotation
and what do I have before and after?
And then we're asking questions now
about more fine tuning the system
in regards to when do I plant, when do I terminate
and how do I manage that in my system?
So my question always to my growers, and it depends,
you know, what state I'm speaking in or where I'm at,
but for us in Kansas,
our key target or driver weeds for decisions
in the west is kochia.
In the south half to two thirds,
or pretty well the whole state, Palmer amaranth.
In the Eastern third is waterhemp.
And then we've got horseweed or marestail
as we identify that across the third.
When we often look at a map of Kansas
and the number of cases of herbicide resistant weeds,
we're like the bullseye in the middle of the US.
We almost have the most identified ones.
I'd say that's probably because
we've got awesome weed scientists that find the weeds
and identify their resistance traits and document it.
So they're really good at finding them all,
but our cropping systems are so diverse in the centers,
the weeds are coming in from multiple different angles
that are demonstrating resistance.
We just have a lot of species
that have ended up with those traits.
So we've got a lot of resistance issues to manage,
but these are driving what our farmers are thinking about
in their system
and want to manage using cover crops to some extent,
because of the resistance that they may have
in those populations.
And so, what's my targeted weed?
What cover crop will I plant and when?
Will help me, if I know the weed, when to do that,
because when I know when that weed
is going to germinate and emerge,
then I've got a better idea of
when I need to get that cover crop in place
to be competing against that weed species
that'll be starting to appear.
And so in general terms, when do I need a summer crop?
So, let's say, in my fallow after harvest of wheat
before I've got, you know, another summer crop
through that fall winter time period
will let me go after horseweed and kochia,
and I'll show some information on that.
And in Kansas, we have enough time
that we can get an early spring cover crop seeded,
say, late February into March
with enough growth before a summer crop,
and that may be a better target to go after
my Palmer amaranth and waterhemp pigweed species.
So again, just how did I end up with thinking of those?
Justin Petrosino had done some cover crop research work then
in the early 2000 to 2007 to eight and nine,
where we were looking at kochia in Garden City,
so, the far southwest part of the state.
And we had planted spring cover crops,
a diversity of species,
and we were looking at, you know, kochia density
and their biomass in response to a cover crop.
So this is cover crop biomass increasing on the right
and how much kochia biomass did I get.
And when I look at these figures, it's like,
there's no relationship there, there's no information.
I'm not seeing that the cover crops are impacting
what my kochia is behaving.
And when we think of those spring cover crops,
and when we know when kochia emerges,
they were happening at the same time.
So I was not getting that cover crop ahead and in place
to feed out that kochia.
So these were getting planted into February and March,
kochia in Kansas will start coming up
as soon as the snow melts and it's a little bit warm,
so late February or early March,
and they were just equally competitive.
So what kind of cover crops
will go after kochia more effectively?
So we evaluated then also fall covers in that same study.
And we could compare cover crop biomass.
I was getting more productivity.
This is in grams per meter squared relative to my fallow.
And we could block out that as I increased that biomass,
I could dramatically reduce the kochia biomass
that was happening in those.
And my triticale, fall cereal mix,
with some of the broadleaves
clearly suppress them dramatically
and reduce the biomass of those kochia.
And so I had a good level of suppression.
So let me step back.
When I say weed suppression,
I'm not getting control, per se, but I'm thinking,
how do I reduce the total number of weeds that are there
and their size?
And so, I've got fewer weeds to deal with,
as well as they're smaller.
That's a lot easier to manage from the other tools.
So the cover crop helps me get me there.
One of the other interesting points
when I've shared this data
is how much biomass do I really need to suppress kochia?
And often, when you speak with folks in the Eastern US,
you need five to 10 times more biomass,
is often what they're reporting.
And a colleague said, well, I only need to get to here.
I'm getting enough suppression with that level of biomass,
you know, 'cause even if I add more biomass,
I'm not getting, per se, less kochia
or I'm getting equally reduced kochia.
So that's always an interesting thought.
So, looking at how much biomass do I really need?
What is that biomass doing?
From a weed suppression, maybe I only need this much,
for other benefits I might need more,
but we're seeing some benefit at that point.
So I'm borrowing this.
Folks know Rodrigo Werle as a former grad student here.
And he came and visited K-State a couple of times
and talked about some of the
emergence profile work that he's done.
So kochia, we know it comes up really early,
and have done work with that,
multiple populations in multiple places.
I usually bring this data in from Rodrigo
to talk about when winter annuals emerge.
So in growing degree days,
this dashed line here is the first day of fall,
first day of winter and then spring.
So we don't accumulate a lot of heat units, of course,
between December and March,
but clearly the order and the rapidity of certain species
and when they come up
tell me that I need to be going after 'em
in different times.
And so, there was one field I was out in August
and I could just tell the Downy Brome was coming up
and it totally made sense
based on this first line that's here
and others that'll come up later.
And so for me,
if these are weeds I want to suppress with a cover crop.
I need to get the cover crop out there prior to
when those things are emerging.
And then thinking from the summer annuals,
here again, kochia.
This was out of Iowa,
so I always tell my students
just shift this about a month or two
based on the calendar from Iowa to Kansas.
But we can see the same order and just how quickly and early
those kochia will come up compared to, you know,
where the pigweeds are coming in
and being out all all year long.
So again, for a cover crop,
when do I need to get it established and in place
and residue out there to reduce what those weeds are doing?
One of the weeds, though, that I said was a driver weed
that Rodrigo didn't end up with in his particular study
was horseweed or marestail.
So I had a graduate student and we found locations
from the northeast corner of Kansas
all the way down to the south,
where we laid out these rings and field edges
where horseweed was found
and documented emergence profiles that were there.
And so, we would pull out of one ring and leave others
to see how well they did over the winter time.
And so, we followed those through a couple of years.
Again, like, this is a dime and that's one plant with,
I don't know how many weeds.
They can put so much mass and size
and make that more difficult when they are that small.
So here are two emergence profiles.
One's the first fall-winter,
and then the second fall-winter
where we went back to those populations.
They're going from, on the legend here,
from north to south across the state,
and this line represents the first day of winter.
And so the goal was, you know, December 21.
How much comes up early before and how much comes up late
with a thought that as I go north,
most of my horseweed should be emerging early in the fall.
Does it emerge in the spring when I go further south?
Do I see it later?
Because a lot of the reports out of other states were,
oh, that's a spring weed, I don't need to,
that's when I need to worry about it.
Whereas we wanted to know,
should I be caring about it in the fall?
And clearly, even across these multiple sites,
everything was happening in that fall.
So this is from zero to 100% emergence
and most were reaching 75 to 100% in the fall.
And the same in the second year,
some were a little slower.
So this line is the most Southern part.
And so again, we saw a little bit that split the difference
and had some spring emerging, but most is in the fall.
So that means that's when I gotta go after it.
Another graduate student then looked at
different cover crops in addition to the herbicide control
to see, should I do fall, should I do spring?
Should I spray in the fall?
Should I spray in the spring?
What kinds of things do we want to achieve?
So we had looked at, you know, zero suppression, of course,
with no cover or any kind of control,
a series of different winter cover crops
from annual rye grass, winter wheat,
winter barley, winter rye.
Then we had some spring-planted cover crops, oats and rye,
depending on the year and what we had available.
And then we started doing combinations
of a winter rye with a spring post-herbicide, for example,
fall with a residual, fall with no residual,
so control whatever came up in the fall,
a spring and a spring, no residual.
And I want to highlight the winter rye line here
with the 94% suppression in one year
and 96 in the other.
Strictly just the rye,
adding a spring herbicide then got me to
complete control of those particular weeds.
So just the dramatic contribution that the rye will give me
for weed suppression, along with the biomass that's there.
I could get that with the fall residual herbicide,
but I don't have anything else on the soil.
I don't have those other benefits
of having that cover crop present and what it can do.
So we clearly see that worked.
The spring, no residual,
I must've been able to get good control.
The student did those horseweed that were up
and whatever control, and I didn't have any late emergers.
And so, you could get control in the spring, but again,
I didn't have the benefit of that cover crop
and the other value that we see with it.
So that's a pretty consistent message,
the winter rye being effective.
We often include winter wheat.
Our farmers in Kansas look at us kinda frustratingly
when we say we want to plant rye
because of how much foundation and seed we produce
and how much contamination there might be with rye.
So we often don't get to mess around with rye
as much as we'd like,
but if I can get the same benefit out of a wheat crop
that they may use as a cover or some other cereal species,
then I feel comfortable making those suggestions for them.
So some of the,
so there was no question that we want to use cover crops,
but how do I fit it into those rotations
is some of our other questions that we have.
So I'm going to try to go into this next question
about what's before and what's after
the cover crop in your rotation,
how do I fit the cover crop in there
and what's my crops going on?
So I wanted to share this bit of research results
from the central part of the state near Hays.
So we're getting into the High Plains area,
low water environment.
And when I asked in my undergraduate class to my students,
okay, what's good and bad about cover crops,
I can tell who is from Western Kansas
and I can tell who's from Eastern Kansas,
because the Western Kansas students all say,
it's gonna use up all my water, I don't want it
and my Eastern ones are fine.
And so right away,
those are big questions that our producers are asking,
is how much water is it going to use?
Yeah, you may get weed benefits,
but what kind of impact does it have?
So, some studies that have been looked at here,
this was using spring planted cover crops.
So they were put out in March in the fallow phase
prior to planting winter wheat.
So they were planting it in March,
looking to terminate it mid June to late June,
to be ready, then, to plant wheat later in the season.
And this was started with some data from '16 and '17,
and they compared a chemical fallow.
We hadn't terminated it yet, a spring pea by itself,
a mixture of oat, triticale and then a three-way mix.
And a colleague, Augustine Obour at Hays,
had set these up
and said, "I can do the soils part,
"but if you can come and get the weed information,
"that'll be great."
I said, "I can do that."
So these are just some pictures
to show a difference between this three-way mix here
of cover crop in the June,
compared to what was looking in the fallow area
that had not been treated with any kind of herbicide yet
to clean it up before wheat.
And just to summarize it,
in the fallow, I clipped the weeds and counted
and identified and weighed them.
The fallow had 258 weeds in a meter square, on average,
across the four plots' treatments.
Spring pea, I dropped it down to 68 weeds
in a meter squared area.
Triticale oat, down to 28, the three-way mix down to six.
So if I think of a fallow to triticale,
already dropped down to almost 10, 90%
and from fallow to this three-way mix,
I barely could find the weeds in those areas.
So we can just see that dramatic reduction
in those numbers of weeds.
And then again, from a biomass standpoint,
almost 100 grams to, you know,
they're barely something that I can weigh after harvest.
So clearly, again, reduction in density
and reduction in size of those weeds
when we introduced the cover crop and have that mass there.
The same out at Colby.
So this gets us into the far northwest area.
Again, just a beautiful looking cover crop there in June
compared to the after wheat or after sorghum
and a mess of weeds that were there.
So 212 grams, a lot more weight,
and down to nothing in the triticale oat
and a few weeds down in the three-way mix.
So what do the data look like?
The blue bars here are, then,
the dry weights of the cover crop.
How much mass do each of these different species produce?
And then the line, the orangy reddish line,
is the biomass of the weeds
that were harvested out of each of those.
And so we can see the fallow plot had, you know,
significant biomass of weeds,
and then almost nothing under those cover crops,
with insignificant mass produced there.
And that was the first year, in June.
Similar to those pictures I showed you,
consistent message the second year.
This year at Colby,
the spring peas were just amazing.
They had excellent rains, pea stands that were, you know,
tall like this and solid.
I could not find weeds under there.
So that's why we saw a really low weed biomass.
Triticale and oats are in rows that were not closed.
So the weeds poked through there.
We could find Russian thistle and kochia,
but again, in the three-way,
we were able to close that down a little bit.
And so we're really looking at the spring pea
as that legume option in some of our cover crops
for those other benefits that we have.
So sort of overall capture is a message
as I've gone on farmers' fields
and looked at bare to cover crop areas,
looked at these experiments over time.
We're regularly seeing
that I can get 50% or more reduction in the number of weeds
and over 90% reduction in the size.
And so, again, those cover crops are giving me
that level of suppression
to make my other tools work more effectively
as I get into weed management
and thinking of the other strategies I need to use.
One of the other fun things of being out in the field
and presenting this,
and then talking to growers,
either in extension meeting or those sorts of things
is how often they sorta put me on the spot
and they are thinking of how to change the rotation
that they've been following for a long time.
So, wheat fallow,
really common in the Western part of the state.
Visit with these growers,
it's like, I can't make money
with how many times I spray the fallow
and the productivity of the wheat.
So they've shifted to using cover crops and growing corn.
That's a dramatic difference
in what they've put into that system,
but they've made it work
by building that residue layer of the corn
and whatever cereal, rye or cover crop they've got.
So he was making that work.
Another grower that I went to visit,
like I don't plant early corn and early beans anymore.
I wait until June.
I get as much cover crop mass and benefit out of that
and then plant a later June.
Maybe it's a shorter season,
but I'm getting all the benefit
out of the cover crop I want and still getting my yield,
planting my corn late.
In Kansas, you either plant early to beat the heat.
Why not plant a little bit later to beat the heat
and get your productivity?
And so that, you know,
being a crop scientist in my undergrad is like,
this is when you plant.
And it's like, no, you don't have to.
We can shift and start thinking about that
and how do we incorporate it?
So that's always been interesting to hear that from folks.
Why do I emphasize that we want to make sure
that cover crops out there
before those weeds germinate and emerge?
Many of us, when we think of those principles behind it,
I've got that either the residue or I got living mulch
that's reducing the light getting to the surface,
I changed that micro environment
for what the weed seeds need
to be able to germinate and emerge.
You know, it may be moist, but it stays cooler
and our weeds are waiting
for that warmer temperature to kick in and come up.
So if we can shift that,
and I'll show you a picture
that demonstrates that we can get some benefit out of that.
We've got some,
I've got another student that's very interested in
more understanding of the allelopathy side of things.
So we're teasing out some of that in another study
and I plan to talk about it.
So, how do I fit this in a system?
So we were really interested in
those spring covers or fall the spring covers
and how long did this last
to give me some Palmer amaranth benefit?
And so this was done just south of Manhattan.
On May 13th, this is an example of a plot.
This is Palmer amaranth already up.
And this size, it was in a nice, protected area
and it was going like gangbusters really early.
And so we knew
we should've been doing something at that point
because beans were going to get ready to get planted
soon after that.
We used just winter wheat
as one of our cover crop treatments.
And so this is just a comparison
of what do these two plots look like
from a non-treated Palmer that's there
versus a wheat crop that I can terminate.
This is what it looked like two months later.
I've got, you know, a good soybean stand,
but I've got that bare soil,
no cover crop residue of any sort.
What we use is the rings to document, you know,
the weed emergence that's happening in those environments.
I just really liked this picture.
My soybeans look about the same,
but I've got this awesome wheat straw residue
still standing in there and reducing
what the weeds are going to be doing.
So what does that look like from a numbers standpoint?
In that study, we had our no cover versus wheat
and the wheat, of course, was planted in the fall.
But then we also added some spring oat, a spring pea,
and then a mixture of the two as another cover crop option.
And the red bars on the left are Palmer amaranth biomass,
and then the blue bars are density.
And so let's start with density.
With no cover, I had lots of plants.
Over 200 in a square meter.
As soon as I got to that wheat cover crop,
I cut it in half, so 50%,
and the same for the mix and same for the peas.
So just having some kind of cover at that time,
when those weeds are coming up,
I could cut the number in half.
But the clear benefit is the biomass.
So the red bar, again, Palmer amaranth biomass, no cover.
I barely have anything in the wheat.
So again, that significant drop in size.
I may have a lot, but they're so tiny.
They're just, you know, delayed in their influence.
Some more biomass in the oat mix and pea,
and I'll show you a picture why we see so much in the pea.
Part of it is we couldn't get enough biomass there
compared to what we were getting in the wheat.
So this is cover crop biomass productivity
from those different treatments.
Just to show, we were still learning how to do peas.
And so I got rows of peas which looked great,
but the Palmer clearly fit in between those holes
and the residue does not persist very long.
So we don't see, two weeks later,
that same level of residue left.
This is the spring oat,
and clearly we could still see some good residue in there,
suppressing the weeds in those areas.
This was interesting.
So, we tracked Palmer emergence through time
and those different treatments.
Again, this is on a calendar basis.
And this particular one, the black line represents no cover.
Than my two cereals, wheat and oat,
and then I got the blue lines here for mix and pea.
And so this is a initial emergence
through a 100% of Palmer amaranth.
And what I want to do is just illustrate
the time to 50% emergence.
With no cover, 50% of my weeds had emerged May 19th.
We don't see as much of that.
We have tried things in that wheat fallow,
like after harvest of wheat,
what can I put in that timeframe
to go after some of those winter annuals.
We've used Sudan grass, sorghum Sudan grass, for example,
and seeing some examples with the rapeseed and brassicas.
But if you think of, you know,
things like the turnips or the daikon radish,
you don't get a lot of biomass.
You just get other benefits, I think,
out of those particular cover crops
versus the same level and suppression,
but we haven't spent near as much time
on comparing all of those.
Student: (indistinct) by using glyphosate?
-: And we have a lot of folks
that are very interested in grazing.
And another issue with buckwheat
is that it's also a contaminant in wheat,
and that's a big no-no.
And so then we got a lot of people that look at us and say,
try to avoid those,
that'll cause me economic heartache in another crop, so.
I know, it's good for pancake mix, but
you have to find a nice wheat-buckwheat blend, I guess,
to try to get that to work the way you want it for later.
So my take home with this one,
with no cover, we saw a lot of that Palmer amaranth emerged,
50% of it by May the 19th.
With the use of those cover crops,
we pushed that emergence almost a month later.
So, if I plant my beans at this point in time,
they're going to be ahead by a month
compared to those little weeds
that are trying to come up later.
So I've got my crop ahead of it.
I've used that residue to push those weeds later
and that's easier to manage at a later time.
And so, just that shift
in potential time of emergence of 50%.
And also, we know that I got fewer under that canopy.
And so, you know, this is just rate of emergence,
but I've got fewer of them at that point, as well.
So some benefits of including that in there.
As always, the growers say,
"Well, what kind of yield did you get?"
And so we had looked at plots that had no residual herbicide
in that cover crop termination side of things,
as we were looking at, you know,
strictly a post-emergence, no resid,
and then with a residual herbicide or pre-product.
The red lines then show
a no cover crop yield pretty poor on soybeans.
And by just adding the residual
allowed me to manage that Palmer longer into the season.
Of course, even with all that wheat residue,
we clearly were getting great soybean yields
compared to the no cover,
and not different once we added the residual herbicide,
but we were getting still great benefit out of those covers
or yield productivity at the end.
So,
better than no cover, for sure.
Some other studies
that I just want to spend a few minutes on
and highlight a couple of key points.
So another student that recently finished, Melinda Smith,
was really interested in trying to understand
some more about cover crops in before corn.
So we had a couple of sites over a couple years,
looking again at a triticale.
She wanted to look at pea
to see what the nitrogen contribution might be
towards the corn crop.
A mix of the two and then no cover.
And then we are looking at
two different termination timings.
So this gets to that other question of
how do I manage this cover crop
relative to my crop planting?
And so, she terminated it at about three weeks ahead
and then at planting itself,
and then also had subplots
where we were looking at fertility to see what kind of,
if there was a benefit out of that pea on corn yield.
And in the end, we really didn't see any yield benefit.
Sensitive here.
So just some results on cover crop biomass
out of the two locations.
Depending, so one of the benefits of terminating early
is that, you know, your cover crop is dead
and that it's not competing with your corn,
but that opens a big window
for when these summer annual weeds are gonna start emerging.
And so what do I have by the time we're planting?
So that's, those are the two parts.
Clearly, if I wait three weeks,
I'm going to get more biomass.
Here, the pea,
you know, significantly more biomass production
in those three weeks,
double my full mix.
The problem in 2019, it was so wet
that my termination timing of three weeks
ended up being,
I needed to plant and the triticale was at a heading point
and I had to terminate it then.
So everything had to get terminated at three,
and we couldn't wait until at planting
because it's getting too far ahead.
So that's why I have no data,
but we clearly can produce quite a bit of biomass
in those areas.
This full mix then,
clearly we have a good amount of biomass at planting
compared to what we were generating
if we terminate it three weeks.
So just the benefit in biomass production
in those three weeks prior to planting
across those two years.
And this just shows what that looks like.
This is the peas at termination,
at planting termination.
We had a lot of pea productivity, good nitrogen production.
The second year, this is what the triticale looked like
at time of planting.
This was when it was terminated three weeks before.
Not too bad, but if I didn't have a cover,
I had significant pigweeds coming up at that point in time.
That's solid Palmer amaranth,
the green sheen that you see there.
We had lots in that field site.
So what did the densities look like?
This was in Manhattan, 2019,
where we just kept delaying, delaying, delaying the control,
but I had no weeds at,
even in the three weeks before planting at that time,
compared to the no cover, where I had over 100,
almost 100 plants.
And so we could get a dramatic reduction
in what those cover crops were doing.
Again, these were almost complete,
a large size that was out there.
Similar to the graph that I showed with kochia,
this is looking at cover crop biomass production.
This is focused on density, rather than biomass,
of all the weeds that were in the plot.
But again, we have that relationship of
as I increase that biomass,
I can reduce, in this case, the density,
and again, the biomass would probably be
a more dramatic reduction down.
But we see that consistent relationship
of increasing the biomass and reducing density
and biomass of the weeds.
One of the last set of studies
that we've been working on with our group
is the termination timing.
So you may hear growers talk about planting green.
And so what does that mean?
How do I optimize that?
Because I still want to produce a cash crop,
but I want to get all the benefits I can
out of the cover crop.
And we need to think about that termination timing
from a standpoint of what weeds do I have at that moment
and what kind of cover crop do I have,
because some of those will freeze out
if you're thinking of going into the winter.
So I don't have to worry about it.
Others, you need a specific timing,
like triticale, rye, at the, you know, blooming stage
before it sets seed,
because we don't want that as a weed in future years.
So, things about that.
And do I include a residual herbicide
in that termination mixture,
or do I just kill the cover crop
and then do something else for weed control,
but that adds another pass to the system?
For a long time, the standard recommendation was sorta,
hey, make sure you terminate it two weeks before you plant.
But again, that opened that window of, you know,
prime time for weeds to come in.
And so what do I do?
How do I optimize that?
My caveat always to speaking with growers
is you've got to make sure you identify your rules.
And those are constantly changing now because
NRCS insurance agents,
FSA recognizes the value of cover crops,
but they still want to protect you from losses
caused by cover crops on your cash crop.
So this is a current map of termination timings
for the country.
And when we look at Kansas,
we have all four zones across the state.
I've got anything from I can terminate it
as long as it happens before a crop emergence
to the point where I'm supposed to terminate it
35 days or earlier.
And so, we wanted to understand that across the state
and optimize that a little bit better
in order to give more information to our own producers
on what that would look like.
As I looked at it, then for Nebraska, you got two zones.
So either 15 days before, so that two week window,
or you could do it at planting,
unless you had some other aspect to it.
So these are constantly getting updated
in the sense of their understanding
and what we're providing, as well.
So one of my PhD students right now
is looking at efficacy of different pre-herbicides
in combination with the burndown application on cover crops
and Palmer amaranth and timing.
And part of the question, let me double check, is
what pre-herbicides do I put in there?
And are they only soil active?
Or do they have some foliar activity
and I lose it in the cover crop
and I don't have it then available
for the weeds that are potentially coming up?
So Ednaldo had set up a study where he had no cover crops.
This was terminated early.
What happens if I've already terminated the cover crop
and then put the soil applied pre-herbicide on?
Or what if I do it in combination
at this green cover crop standpoint?
So I've planted in, I've sprayed,
I've done everything while it's still a green crop.
One year, we looked at triticale winter pea as a mix.
The next year, we couldn't get it planted in the fall,
so we did a high spring oat population
and then did those cover crop treatments.
The products that we were looking at,
several of our pigweed populations in that area
are PPO resistant.
So we wanted to investigate
a couple of the different PPO products
that were soil applied,
as well as S-standard, S-Metolachlor group three,
Metribuzin group 15,
and then the PPOs that he wanted to look at.
We know that S-Metolachlor is only active on soil.
All the other ones could be on soil
as well as on the foliage.
So we wanted to check and see
if we would lose control of the weeds
because it's tied up in those cover crops.
And so this is just a look at one of the reps.
So again, this is a no cover crop,
and guess what's growing there?
We've got lots of pig weeds that are coming up.
So this is the dead cover crop,
and then the green cover crop
that he was looking at putting those treatments on.
So this is two different years.
2020, looking at the non-treated control
through Flumi, Metribuzin, S-Metolachlor,
Saflufenacil and Sulfentrazone.
Almost all of them worked just fine
with or without the cover crop.
The one significant reduction
was actually in the no cover Saflufenacil.
So I didn't see any impact of any of my cover crops
on that herbicide activity, but I had a,
Saflufenacil does not have a very long residual period.
It's fairly short.
And so, basically, probably controlled some of the weeds
and the rest (indistinct).
The only other one that was a little less was Metribuzin,
here at this point, but not that different.
But again, the same story,
probably a lot of weeds were up and didn't get good control.
We didn't see any impacts the second year.
So in that sense, combining your burn down
along with your soil-applied products,
we didn't see any impact
on spraying it on live material versus dead cover crop.
So we can make that feel comfortable,
more comfortable, in that recommendation
for our growers to do one pass and get both,
kill your cover crop and put your soil-applied down.
Next questions, though, are
I've got those cover crops or weeds.
What do I, what does that look like on crop establishment?
So we do see some potential impact.
With no cover, I've got, you know, not bad.
Stand, still pretty good
when the dead cover crop two weeks early.
But when I planted green in this particular case,
maybe I've got some issues on stand establishment.
So that's our next question.
I've got a great weed suppression and I want to grow a crop,
so what do I need to make sure I'm doing there as well?
Different methods of terminating.
Of course, we've done a little bit of work
comparing a roller crimper to, say, a herbicide.
Only works for certain things and at the right time, again,
compared to something that you want to be careful with,
but we were looking at corn termination timing.
Again, five weeks before, three weeks before
versus the time of day.
And so here again,
we've got just this great stand of residue,
corn coming up in there.
If I had a cover crop with no residual
that I terminate at five weeks,
I've got a horrendous weed problem.
And so, the cover crop is clearly giving me
that benefit with no residuals.
This was supported by our Kansas corn commission
and looking at termination timing.
This one just set up really well with a cover crop,
no residual, only the Roundup,
but good residue from the cover crop in there.
Weed counts in those particular plots
with no residual herbicides,
so strictly looking at the cover crop
and terminating it with glyphosate, for example.
I've got lots of weeds five weeks before.
So I counted this, you know, in season,
but lots of weeds if I'd terminated it so early,
but if I'd terminated it the day of planting,
the number of weeds in there is dramatically lower.
That cover crop's just got that benefit.
If I included a residual,
I'm getting excellent benefit of the residual herbicide.
along with that cover crop.
Here again, too, I've cut my weeds in half
with no residual herbicides.
So what's the cover crop doing?
Quite a bit.
And overall, less weeds when I include
a residual herbicide in the system, as well.
Corn yields were not different.
And so, that's always our other message
that we want to try to see,
is if I planted on the day of planting,
I've got my weed benefit, but have I impacted my crop?
Sure, it's a little bit variable,
I've not got a significant loss here, too,
if I did or didn't do it.
You see the same in soybeans.
So this was on a grower's field,
one week at planting or one week post,
looking at different stages of the cereal rye
when it was terminated.
So it was only 25 centimeters
and not a lot of mass at boot stage
and then later at heading.
On June the seventh,
when we went and evaluated what do the beans look like?
We saw some reduction in size
when we waited that one week post to beans,
but we saw no weeds in there, either.
So what are we going after?
And actually the yields were not different
when we waited 'til that one week post-termination timing.
So still tweaking the system
to try to understand what some of those optimal timings are
for our growers in managing these two.
So again, my goal today was to get us to think about
what are the key weeds you're going after
and how do I optimize when I put that cover crop out there?
What will proceed, or what will follow the cover crop,
thinking again about where do I fit it in the rotation
and what crop do I have before or after
that I'm needing to manage?
And then thinking about the termination timing
in regards to the cover crop
with the grower's interest in planting green,
what does that really mean from a weed standpoint
and not impacting the crop yield?
So we've got students working on all those different pieces
as we build this system together.
And again, when we think of Kansas,
it's quite diverse from one end to the other,
so it's kind of a unique scenario with each person.
So these are some of the principles that we share with them
in order for them to figure out
how to fit it into their own system
and try it there, as well.
So one of the recent,
this is two years ago now already,
we finally could get the whole group
of the K-State folks together for a picture
at one of our conferences.
So I've borrowed the photo from someone else.
The north central meetings a couple of years ago
with our weed science group.
So my colleagues, Dr. Mithila Jugulam
Dr. Sarah Lancaster, Dr. Vikram Kumar,
and then graduate students in the group there.
So with that, thank you very much for your time,
appreciate (indistinct) presentation.
So look forward to any questions.
Yes, Amit?
Amit: So we have some blending green project.
I was expecting to see, like,
certain (indistinct) time when we plant green
and then terminate after a couple of weeks,
because soybean is relatively less complicated
if you compare with corn.
-: Mm-hmm.
Amit: But in our studies, we have seen
corn had actually hard time to be more resistant
to plant stem issues compared with soybean.
So if you had any suggestion or?
-: So, Amit's question is regarding the planting green
and the difference in corn establishment in that scenario
versus soybean.
And when you're planting green, have you done any
herbicide application for termination yet or?
Amit: (indistinct) termination timings, like,
two weeks before blending by using glyphosate.
-: Mm-hmm.
Amit: And then two weeks after.
-: Okay, so two weeks after.
So you planted and then terminated.
Amit: After two weeks.
-: And so is the corn and the beans
planted on the same days?
Like on the calendar?
Not like, corn's normally an earlier crop
and then bean's a later crop,
so this was also all at the same time?
Amit: Three years in Nebraska,
at least in south central part of the state,
we are seeing growers.
-: Mm-hmm.
Amit: Have started early planting for soybean.
-: Right.
Amit: And then corn.
-: Right.
And so, some of those things, you know,
people have often said, well, if I plant my corn earlier,
it's cooler and wetter under that cover crop,
and so that may impact my stand establishment versus beans.
It may be related to their emergence types
from an epigeal versus a hypogeal kind of thing,
to be able to get that plant up and established.
But I've heard the same thing,
that soybeans seem to be able to better handle
planting into a cover crop and growing
versus what corn can.
And so, I've heard the same thing, I have.
I don't know why,
but especially 'cause they're planted on the same date.
So, do you have any ideas yet?
Amit: Not yet.
Let's see how it goes with the second year, of course.
-: Yeah, yeah.
Again, yeah,
just what kind of stand establishment do we get?
Are there, you know, if it's cooler, wetter,
are there other pests that are, you know,
that the corn is more susceptible to, say, than soybean?
Student: Have you seen stand reductions?
-: I haven't.
No, so when the students have done it, we haven't.
Student: (indistinct) the introduction.
-: Right.
So the other question was do we see actual stand reduction
versus, I don't know, are you saying stand reduction
or you saying just quality of the stand or?
We have not observed
that we've had any reduction in our stands
across the treatments that we're looking at.
Student: What if you show the relationship between
(indistinct) biomass and cover crop biomass?
-: Mm-mm.
Student: What if you did kochia and Palmer amaranth?
-: Yeah, yeah, we've done it with several,
any student project that's got that kind of information
and try to generate that same curve.
Student: We've done similar things here.
And it was interesting.
I pondered this, if there's,
it's really noisy and low cover crop or biomass,
I trim the weed.
And the weeds are very (indistinct).
-: Right.
Student: It seems like there's a threshold at which
cover crop biomass hits a certain point.
And also that relationship.
-: Right.
Student: Tightens up if you (indistinct).
-: Yeah, yeah, so.
Student: (indistinct).
-: How much?
Student: Yeah, where is that point or what's driving?
I don't know.
-: Right, so, like I say,
the relationship between biomass of the weed
relative to what we see with that cover crop,
increasing cover crop biomass,
there is a very neat relationship.
Like you say, very noisy at the beginning.
So at what point do you have enough mass
that you're probably doing enough cover of the field?
You know, whatever land area you're looking at,
enough shading, there's probably some other metric
other than just mass that we could look at
to say when that is.
But I remember a colleague, I think Steve Mirsky,
has data sets from east to west.
And he's a USDA wheat scientist, does cover crop work.
And I remember at one of our conferences,
he showed sort of the different pictures
and the amount of biomass in the Eastern US you needed
was incredibly high.
And I was like, we don't need near that much here.
And I don't know why.
So what is it about, you know,
what do we need for our weeds here compared to there?
John, got an idea?
John: I was thinking the same thing where,
you know, even at the very beginning
you showed a slide that showed no relationship
between weed mass and cover crop weeds.
Then you showed one where your weed mass
was like 15 grams per square meter.
And so, you were way down near zero.
-: Yeah.
John: Then it was like at 150 to 200 grams of cover crop
per square meter.
But that's only 15 grams.
Later on, you had like as many as 400 grams of wheat mass.
Now, to me it seems like that matters.
And it works the same way, I think,
with the critical period.
Is how effective is it is or how broadly critical
(indistinct).
And how effective the cover up mass is
is totally dependent on.
-: What kind of weed population you have.
John: How much wheat you actually have.
-: Yeah. John: Right?
And so,
to me it seems like it depends.
How much cover crop you need is dependent on
how much you started with.
-: Right, what your weed issue is to start with.
So again,
tying back to what your starting population, maybe,
that you're trying to measure or
influence with whatever cover crop that you have.
And our environment's stressful enough
that maybe we just don't.
Yes, you got one online?
Steve: You have an online question.
Do you have any information about spray deposition
of pre-herbicides over cover crop canopy,
corn or soy assisted?
-: So, the question is related to spray deposition
as you get into those canopies.
I know Ednaldo had put spray cards out
when he was looking at the different current timings
with no cover, a dead cover and the green cover
with those soil-applied products.
I don't know what those look like at this point in time,
but basically he was able to, you know,
are you getting it all the way through
down to get the weeds?
But we saw that we didn't have
any reduction in weed control,
which was evaluated, you know, three, four weeks later
where those products were applied.
So we don't know if it's hung up in the canopy,
but eventually it gets on the soil and is managing.
Another question, Amit?
Amit: So in last two to three years
I am seeing (indistinct) is emerging
very early in the season.
That was not the case, maybe, before five years.
Like you see previously where it was
somewhere in the middle emergent species.
It generally starts in May or after May.
-: Right.
-: With waterhemp.
But now, at least in last three years,
I'm seeing an increased amount (indistinct) species
and it emerges almost in like beginning of April.
By the time we (indistinct) emergence,
(indistinct) is there (indistinct)
-: Mm-hmm.
Amit: So are you seeing that in Kansas area,
or it's typically south central Nebraska right now?
-: So the question is time of emergence of velvet leaf.
And what we're seeing now is it's shifting to being earlier
or, you know,
I know wherever I see any land disturbed,
so let's say, you know,
an area where we got a lot of these terraces,
we call them bump up terraces.
So they'll till those.
So they get exposed,
whereas the rest of the field may be no-till.
You bring up the velvet leaf seed
and they're up there early.
So the warm,
I don't know if there's areas where it's warmer,
but they heat up a little faster.
But they're definitely early,
but I don't know if it's in no-till.
Amit: (indistinct).
-: I don't know.
They're usually one of the first ones I see
after kochia and lamb's quarters, for example,
out in the field.
But I don't know if the main flush.
Oh, yeah?
Even then?
That's early.
Yeah, I don't have an.
Amit: Mare's tail, giant grass weed, common grass weed,
and then velvet leaf and then (indistinct).
-: Oh, okay, so, yeah, that's different.
Amit: Early April emergence.
-: I don't know.
Have to track that one a little more.
That's interesting.
Student: Have you done any other work with your
(indistinct) versus the organics?
-: Nothing directly.
So the question was have we done any of this work
with actual organic producers and their systems?
No, not directly with anyone that's looked at that,
but that's one of the,
the one study we did look at termination timing
using roller crimper in case that was going to be of value
versus using the herbicide side of things.
And we based our timing of roller crimper on
when the rye hit the right stage.
But we were trying to lay down, say, annual rye grass.
That didn't work.
And that's one that we don't encourage.
A lot of the broadleaves, it won't work very well.
So again, it's a tool that has to get optimized
based on the cover crop,
but that would be one of those alternative ways
to get that into a system without a herbicide.
John: Yeah, I wonder, you know,
if these are really effective,
wouldn't you expect that weed seek bank to reduce over time
if you had a really good system in place?
-: So the question is getting a system
where we have these cover crops in,
are we potentially seeing some change in the weed seed bank?
We're interested in looking at that.
We've got students now looking at,
if I have seeds in the seed bank,
is there something different about that environment
that'll maybe decay those seeds faster or not?
But clearly, if we're allowing
fewer weeds to get returned back to the seed bank,
fewer seeds getting produced to go back to the seed bank,
believe the dynamics benefit.
We are seeing maybe reduced density,
but a lot of those weeds are emerging,
but they just can't make it.
And so, we are seeing loss out of the seed bank,
but they're just, you know, they're small, tiny,
and they're getting, you know, decaying in that cover crop.
So interested in sort of that longer term kind of thing.
Yeah.
So there's multiple different ways people are exploring
the impact on that seed bank with the use of cover crops.
So one is have I changed the soil environment in some way
to the benefit of seed decay?
Or are there other things, from a management standpoint,
not returning seeds?
So, yeah, good question.
Another one is, yeah?
Student: If you did any work on seed banks initially
before you started any of these experiments?
Or anybody (indistinct)?
-: So, like I said, right now we have a new student
that's just starting to look at that.
And so we're looking at the two different pigweeds species
and putting that into the soil environment to see
what kind of impact.
Yes?
Steve: We have another online question.
Eventually if growers include cover crops
as a weed management strategy,
how likely you can see reduction
in selection for herbicide resistance?
-: So the question is related to
development of herbicide resistance,
and can we reduce the selection pressure
when we include cover crops?
We can just include
multiple different weed control practices.
So cover crops are one,
anything we do with our crop production system,
you know, row spacing, seeding rates, competitive crops,
where we can reduce, you know,
the number of times a particular product is used
or the number of
even the range of products that we would need to do,
anything we can do to mix it up for weed control
should allow us to do that.
So I clearly see that cover crops,
even though we use,
often, a herbicide to try to control it,
should be reducing that selection pressure.
So,
that's always our challenge,
but we've got to keep tabs on what we are putting out there
to actually be able to get a benefit out of it.
Yeah?
Student: (indistinct) you can get away without
any herbicide program and still have a pretty high level.
Especially, I think, as a coordinator, (indistinct).
-: Right.
And again, that is,
so the comment is with some of these systems,
it almost looks like if you get enough cover crop
that you may not need a weed control program.
So the one farmer that had worked on his particular field
comparing what if I did a cover crop versus no,
we could totally substitute one of the application timings
with that cover crop, but still in the whole system,
we needed to go in and do other,
you know, management strategies.
But basically he could substitute that,
say, fall burn down, pre-herbicide program
with the program that he had with that cover crop out there.
And so we could see a substitution of one of the passes
with using the cover crop, but still would need some,
'cause there's, again, I always go,
well, what weed am I worried about?
There's other weeds out there that I need to also go after.
So I can't forget them in the whole scheme of things.
So there may be later ones that are coming up
that we need to worry about.
Amit: Soybean started like using planting green?
-: Mm-hmm.
Amit: To terminate after a couple of weeks,
then they don't apply any post-treatment herbicide,
but then they also apply just some residue products
after termination and after a couple of weeks.
Because in soybean, you can apply direct
at least fix or six herbicides.
-: Mm-hmm.
Amit: There are only residual activity.
-: Right, right.
Amit: You can apply post-treatment.
And so, I guess the trend I have seen
with some soybean growers.
-: So are they, so they'll put some, so the comment is
with some conventional soybean growers now,
they'll plant green.
Amit: Yes.
-: Even terminate that much later, two weeks later.
Amit: Yes.
-: And they include a residual then,
or then even later a residual?
Amit: Reapplying residual product
before pulling up their weeds (indistinct).
-: Right, right.
So you want to try to get ahead of the rice
with that residual.
So you'd still wants that combined program.
Yeah, yeah.
John: So, that question that Amit asked
(indistinct) what I was going to ask.
Like what percent of the
use of cover crops been terminated
prior to crop planting
versus the crop was planted into green and terminated later?
-: I don't know what the numbers are, but I've not.
Student: I mean, the majority is probably
terminated before planting.
-: Right.
So what I've heard, you know,
in speaking with other groups and what people have found
is that if you terminate it early and you try to plant,
you've laid that cover crop down.
And if your equipment's not set up
or you have a hard time getting in,
you might crimp and have problems.
If you terminate it within the week of planting,
a few days before or after, it's still standing.
And it hasn't totally all fallen down,
and that makes planting through it a little easier.
And then, again, that same, you know,
if your cover crop is still gonna not get to a stage
where it's producing seed and gonna be a weed itself,
you can terminate it later.
But the benefit of it still standing
to plant a row crop into is of benefit.
So I see that shift to more of that planting green,
depending, it could be already sprayed
but still standing kind of thing.
It's a benefit.
Student: The reason I asked that question is,
this might be a long shot, but I'm going to just,
I think I talked to Chris about a year or two ago,
like you if plant into the standing cover crop, plant green.
-: Mm-hmm.
Student: And then you use the concept of
critical grid of weed control to determine the timing
for removing that green,
so in a way, you're treating cover crop as a weed.
-: Right.
Student: So how long can you keep the cover crop "alive"
before we go in and based on all of our work
that we've done with critical period in corn,
that is the third leaf stage,
you gotta take them out by third leaf stage.
Or in soybeans, you gotta take the weeds out
by the second (indistinct).
-: Right.
Student: So I don't know how does that relate to
what Amit was saying earlier?
You know, when they,
with that second triticale might be
right at that two weeks after planting.
And to relieve (indistinct) the green stand.
So we might be all getting the same emergence,
you know, from looking at it from different angles.
But, I don't know, it would be interesting
just to actually do a critical period study
or using the concept of critical period.
-: The other flip side to that
that people are interested in is interceding a cover crop
and how, you know, what's my end of my week three period.
Student: Right.
-: To be able to then do that on the other end?
Student: This is what, again,
that's why I asked you about our organic guys.
-: Yeah.
Student: Since the organic guys
that are actually planting that, like,
months before harvesting corn.
-: Yeah.
Student: You know, they'll do,
they'll fly the helicopter, drop the seeds.
-: Yep.
Student: You know?
-: Or you've got the heavy spray machines,
that's got the outfits dropping in a row of seeding,
or even earlier where they'll actually go in
with a drill of some sort and (indistinct).
So there's a lot of neat ways
that people are trying to figure out how to
intercrop and mix.
And we think of from a weed standpoint,
how do I protect the crops as much as I can
and use that kind of critical period of weed control timing
to either make sure I terminate it before I hit that?
Or maybe I can introduce that cover crop
after that stage, so.
Amit: So what's our time (indistinct)
in soybean in Kansas?
-: I haven't seen it that much.
You know, there's the,
people are thinking about it.
And I know there's some of those examples
where they'll plant a couple rows and leave a gap
so that they can plant the other crop in there.
I haven't seen really anyone doing that,
but there's probably someone trying it, so.
Yeah, another question?
Student: Two, actually.
-: Okay.
Student: The data you show in regards to emergence timing
of a wide spectrum of weeds provides a great method
to fine-tune cover crop planting utilization.
Does the emergence timing stay fairly similar
as you go west to east,
or does it change markedly so that other areas
will need to develop the same sort of data
to help guide cover crop establishment timing?
-: What I've, so the question is
using those emergence sort of sequences profiles
and how does that relate to developing, you know, timing?
We probably, I think the order stays the same.
If you have those weed species in your area,
the same timing, 'cause they have the same sort of
environmental requirements,
no matter where you are,
but it may be on the calendar you'll have to adjust for
you know, what the environment is
in Western Kansas versus Eastern, or North or South,
just based on when you reach those thresholds of temperature
and get the moisture conditions.
So I think the order is the same,
just when you need to look at it
on your calendar might change.
But I don't see that.
If it's a winter annual, it's going to be a winter annual.
And so you still want to adjust your cover crop
based on that.
Student: (indistinct) and moisture.
-: Yeah, and moisture is probably more east-west.
Should I or shouldn't I do a cover crop and (indistinct).
You said another one?
Student: Yes, I have one more.
If there are a stage
that cover crop seeds following termination,
and this occurs frequently,
would we need to be concerned about
the volunteer plants of any species
becoming resistant to herbicides,
creating new issues, question mark.
If so, which species do you think we should watch out for?
-: So, a concern of
incomplete termination of cover crops
so that you might have seed left that'll come up later
and they're getting exposed to herbicide control,
getting selected.
Would they become resistant?
There's always that chance, I guess.
I don't know what.
Very little.
Most of them are are,
you know, if you think of it, are crops,
so they don't have the dormancy traits
that would potentially, you know, push you into that.
But, you know,
unless you're planting a glyphosate-resistant canola
as a cover crop or something, you know,
where you know that trait maybe in there.
Or a, hopefully, again,
part of the benefit of cover crops
is that it's part of an integrated system.
And we've got so many other tools
that we're hoping these growers are
looking at and thinking of
and use that as part of that whole combination of things.
Amit, what are you thinking?
Amit: To follow up with that comment,
my concern is, see, most of the growers
they are using glyphosate very commonly,
like about 99% of growers are using glyphosate
for terminating cover crops,
whether it is cereal rye or wheat or any other species.
So my concern is maybe in the future,
I think because they applying early in the season
when winter annual weeds are present,
so maybe future my concern is we might have
some winter annual weeds like hempweed
and (indistinct) cress
and Kenzie mustard.
There might be more resistance to glyphosate
compared with any of the cover crops.
-: So maybe some of the weeds
that are getting more exposure than they used to
to a single product because of,
that's what we use for termination.
So we may need to think about more diversity
in the termination of products.
And I know for a lot of the broad leaf cover crops,
they recommend not just glyphosate,
but that you include 240 or camphor
or some other growth regulator
in order to make sure you get better termination,
which would also benefit any weed control (indistinct).
Amit: This study you see alternate use of glyphosate
that we can use to terminate particularly cereal rye.
-: Right.
Amit: Which is most common in Nebraska.
And you'll see some good advantage.
None of them are as good as glyphosate,
because glyphosate is, of course, very great grass healer.
-: Mm-hmm.
Amit: It can knock down cereal rye easily.
-: Yeah, yeah.
Amit: But then, quickly,
about using some of those (indistinct).
-: Yeah, yeah.
Amit: With herbicides, that they are slowing things.
So we have seen cover crop biomass was present
longer period of time and it suppressed weeds,
particularly summer annual weeds,
like waterhemp and Palmer amaranth,
longer compared with when you use glyphosate to terminate.
Student: The other herbicides don't have issues
with the size of the cover crop.
-: Right.
Student: They can solve the small guy,
but when you get that food stage.
-: Yeah.
Student: Right, you don't have any other (indistinct),
except glyphosate.
-: So, people may not have heard sort of your comments,
so I'll try to restate,
But the idea of
not needing to look at other products like glyphosate
to terminate cereal.
So ACC, ACE inhibitors, and just what that behavior is
and how do we fit that.
Yeah, select and yeah, yeah, yeah.
Just takes longer for them to act even compared to.
Amit: And so biomass was present
for a long period of time.
They tend to suppress it.
-: Yeah.
Amit: Particularly for summer annuals.
-: Because of their slower action,
then we've got that biomass, whether it's green or dying,
present longer in a more upright
versus start to decay stage.
So, you get some longer benefit out of it.
No, that's another one,
just to compare those kinds of products and options.
Not from a weed suppression standpoint.
So the question was how much are turnips used?
We see a lot of growers use that in a mix
where they'll be grazing.
So we have a lot of our folks that'll put cows out on
either corn stocks, sorghum stocks, even beans.
And if they put that in there, that's a benefit for that
livestock grazing.
So for many of our producers to pencil this out,
yes, we see all these other benefits,
but I can pencil it out better
if I have the opportunity to graze those cover crops.
And so, hmm?
Oh, yeah.
So,
other benefits, wildlife benefits.
Hey, I really appreciate all the questions and the thoughts.
These are challenges.
It's a diverse system,
so there's a lot of different things going on,
but it seems to be fitting in for a lot of our producers.
Thank you.
Steve: All right.
(students applauding)