- Our next presentation will be by Jared Goplen.
Jared is a PhD student in the Agronomy
and Agroecology at University of Minnesota.
He's working on his PhD focusing on improving
control of herbicide-resistant giant ragweed
by managing the weed seed bank.
Jared is originally from Canby County
which he grew up and is still involved in the family farm
raising corn, soybean, alfalfa,
wheat alongside a cow-calf herd.
With that, I'd like for you to help me welcome Jared.
(applause)
- Well thank you for the introduction,
and it's good to be here.
I'm representing Minnesota here.
So, I'll just kinda get started here, but...
If anyone of you were at the last presentation,
you kinda heard a little bit about herbicide resistance.
It's kind of on everybody's mind.
It's certainly becoming a bigger issue.
So, obviously there's been a number of weeds
that have evolved resistance to these herbicides.
You know that threatens the obviously the herbicides
for weed control since they're not
gonna be effective anymore.
But you think about some of these
herbicide resistant traits.
You think about 2,4-D and dicamba-tolerant crops,
if the weeds are already resistant to those products,
those traits are essentially worthless,
so it becomes very important to protect
some of these products and it forces us to look
at some of these other mechanisms to control these weeds.
And just to give you an idea, it's been estimated
anywhere from 11 to 20 dollars per acre
in increased production costs with dealing
with some of these resistant weeds,
but you can obviously imagine some scenarios
where that cost would be significantly higher than that.
So that brings us to the main question
of how do we manage these resistant weeds?
Obviously herbicides have been fairly effective in the past,
and there might be another product that can help you out,
but what it comes down to is we need to start looking
at some of these other options.
Something like tillage, or maybe even pulling out
your old rotary hoe out of the shed, or cultivator,
and then ultimately, if we become that desperate,
it might come down to hand-weeding,
but I guess if it was up to me,
I'd just as soon cultivate instead of hand-weed.
There's also these things that
I'll refer to as cultural practices,
and they include things that you see listed on the screen.
So things like row spacing, planting date,
crop rotation, and try to manage that weed seed bank,
and then also, if you're planting annual crops,
maybe think about incorporating a perennial like alfalfa,
and these are all things that aren't gonna necessarily
directly kill the weeds, but they're gonna at least
help improve control by suppressing the weeds in some way.
So, for the sake of today's talk,
I'm gonna kind focus on these bottom ones.
And the weed I'm gonna kind of use as an example
is giant ragweed since that's one of the weeds
I've been dealing with for some of my research
and is becoming a very big problem in Minnesota.
So, those of you familiar...
giant ragweed has been a pretty significant
agricultural weed for quite some time.
It's very highly adapted to corn and soybean systems.
It tends to be difficult to control with
Pre-emerge herbicides 'cause it emerges
really early in the growing season,
typically before you're planting or those Pres are going on.
Then, also, it's very large-seeded.
You see the photo on the right here,
you can see it's about the same size as a soybean seed,
which allows it to emerge up to six inches in the soil,
kinda puts it out of that herbicide band
and makes it a little more difficult to control.
Giant ragweed also has developed resistance
to multiple herbicides as you might have saw
in one of the last presentations.
On Wisconsin, I know it's resistant to both
ALS and glyphosate independently,
but in Minnesota, we have multiple resistant plants,
meaning we have resistance to both ALS
and glyphosate in the same plant.
And these resistant species are becoming
quite widespread across Minnesota
and the greater Midwest.
So, this figure here just kinda shows you
and reminds us the life-cycle of annual weeds.
So, for all annual weeds, you start from
that weed seed bank, that seed'll germinate,
emerge, and if that weed is able to progress
through the growing season, produces viable seed
and starts that cycle all over again.
So for the research we did, we were interested
in how crop rotation can influence
some of these aspects of the seed bank.
So, referring to both the seed bank degradation,
then also the emergence patterns to see how
crop rotation can affect these.
And then look at both of those and see how
they can maybe help improve our weed control.
So, the study took place down in
southeast Minnesota by Rochester.
And at the location we had a farmer that was having
significant difficulty controlling giant ragweed
and turned out it was resistant to both
glyphosate and ALS, so we established
this crop rotation research there.
And the next couples of pictures here
are gonna show you kind of the level of resistance
that we're dealing with.
The beginning of June, we went in
and applied the label-graded glyphosate
on the left and untreated on the right.
And you can see there was a little bit
of suppression on the giant ragweed,
but certainly not acceptable control.
And if you take a look at ALS, for this picture
we used FirstRate and you can see once again
on the left picture that ALS really isn't doing
a whole lot compared to the untreated on the right.
So, a very significant level of resistance
in this population, and I should just also mention
that the pictures were actually taken place
right next to each other.
So, for this study we had six different crop rotations
that I have listed in the table here,
and they're all fairly common in the Midwest,
so you have continuous corn, variations on
a corn/soybean rotation.
The fourth incorporates wheat
into that rotation, spring wheat.
And the fifth is atypical rotation where
we just have a single year of alfalfa
in a corn and soybean system, but we wanted
to see if just even a single year of alfalfa
might have an effect on some of these weeds.
And then the sixth is two years of alfalfa followed by corn.
So, just short three-year rotations just to see if
we can see any differences in that short period of time.
Since we did have resistant weeds, we did plant
LibertyLink corn and soybeans
just to control those weeds, and if we did have
weed escapes, we maintained a, what we call,
a zero weed threshold, meaning no weeds
were allowed to go to seed so we're able to get
a better understanding of the weed seed bank degradation.
So, here I'll come back to this figure
and just to kinda give you an idea,
we're gonna start talking about the seed bank degradation.
So, what's happening below ground.
So, there's a few ways that we can
degrade the weed seed bank, and this really
goes for all weed species.
So, the first and easiest to think about is emergence.
If that seed's gonna emerge, obviously it's leaving
that seed bank and it's not
gonna be a problem in the future.
But then we also have these other things
that you can't really see, which include things like
seed predators, so some rodents or birds
that might be eating the seeds and removing them.
Then we also have soil microbes
that are breaking down the seeds.
So, stuff like bacteria or fungi, some of the same
microbes that are breaking down your crop residue
are also gonna be having an effect on the weed seeds.
Previous research has shown that crop rotation
can increase this activity of microbes,
and therefore increase seed degradation.
So, we were really interested to see if crop rotation
might have an effect on this.
So, to study the seed bank, basically what we did is
we went in the first year and the third year,
just took soil samples, and counted the weed seeds
in those soil samples.
And this graph here shows you the crop rotation
treatment on the x-axis, and the percentage
of the giant ragweed emerged on the y-axis.
This is showing the depletion for giant ragweed.
And as you can see, there's a very high level
of seed bank depletion in just two years.
So, between year one and year three of that crop rotation,
and there was no differences between
any of the treatments like we thought there might be,
and overall, there's 96 percent seed bank depletion
in just two years, which we thought was pretty significant.
And really what that tells us is if we can intensively
manage this system for just two years,
you can see a very high level of seed bank depletion
in a short period of time.
Now, that extra four percent might continue
to cause problems, but at least you're getting
a start somewhere.
One of the interesting things we did notice
with these different crop rotations
is that, like I mentioned previously,
one of the ways you can degrade the seed bank
is through emergence.
Now, these blue bars that I'll just
add on top of the orange ones
show you the percent of that depletion
that was due to emergence,
and you can see in those first three treatments,
almost 100 percent of that depletion
was due to emergence in the corn and soybean rotations.
So, like I said before, giant ragweed is very adapted
to corn and soybean systems, so it isn't really surprising
that we're seeing very high amounts
of emergence in those systems.
But then if you look at some of these
more diverse rotations, so the ones that have
wheat or alfalfa for either a single or two years,
you can see about 60 to 70 percent
of that depletion was due to emergence
in the alfalfa and wheat rotations, the annual rotations.
But that two years of alfalfa really suppressed emergence,
and only about 41 percent of that depletion
was due to emergence, which tells us
there's some of these factors that are playing roles,
like microbes, there could be some other way
that this seed bank is being degraded.
Another example of how this could be occurring
is through just seedling mortality.
So, it could be with the differences in tillage
in that alfalfa system, you know, there's less tillage,
could be a little more compacted soil,
and it could be that those seeds are germinating
but aren't able to emerge due to reasons such as that.
So, to really summarize and put this into words,
if you're able to maintain a zero weed threshold,
at least for giant ragweed, you're gonna see 96 percent
seed bank depletion in just two years
in any of the crop rotations.
But the million dollar question is
well, how in the heck do you maintain
a zero weed threshold, right?
So, one of the examples I'll continue to go into
is planting alfalfa.
So, now coming back to this figure,
and I'll talk a little bit about emergence
and how crop rotation had an effect on emergence.
So this figure here, once again, has a crop rotation
on the x-axis, but now the y-axis is gonna be
seedlings per square meter.
And, basically, this just shows you
the total emergence of giant ragweed
in the second year of these rotations.
So, in year two we had the most diversity
in the crops that were out there,
so we had all four crops that were in our rotations.
So, just gives you a really good example
of what we saw for total emergence in these systems.
And the two treatments that really stick out here
are the second one, this corn that was planted
into the soybean stubble had the greatest emergence,
which is something important and you should
probably keep in mind, especially if you're dealing
with giant ragweed, telling us that some of the soil
environmental differences, you know soil residue,
could be having an effect here, so when you plant corn
into the soybean stubble, we saw more emergence,
so something just to maybe keep in mind...
and be ready for.
The other treatment that really sticks out
is that last treatment.
And that's the second year of alfalfa,
so in established alfalfa, we saw significant reductions
in giant ragweed emergence, which also isn't
that surprising because this is a true perennial system,
so you're not gonna have...
or that giant ragweed isn't very evolved for that type
of system, so it's really suppressing that emergence.
So, just to put that into words, as well,
once again, that corn planted into the soybean stubble
had the greatest emergence, and in that
established alfalfa treatment, we saw five to 13 times
less emergence in that treatment
that any of the other crop rotations.
And the weeds that do emerge aren't as big of a deal
because just with your regular cutting schedule,
you're going to be able to clip those plants off
and prevent any weed seed production
just through your regular harvest schedule.
There's also a number of other benefits
to planting alfalfa.
So, along with these crop rotations
that we had for the study, we also took
crop yields and monitored all the
crop inputs and outputs of the system,
and using the average prices received
in Minnesota for all these crops in 2012 and 2015,
so you can see the prices listed here underneath the graph,
but so about four and a half dollars for corn,
$11.77 for beans, $6.40 for wheat,
and $166 a ton for alfalfa.
This is our average net yearly returns.
So, we have the crop rotation on the x-axis
and then the dollars per acre per year on the y-axis.
And you can see on the far left that two years of alfalfa
followed by corn, even in the last four years
with quite high commodity prices, we still had
the greatest net yearly returns.
But, really the last four years is
quite a bit different than what we're
looking at for prices currently.
So, what I did is just took the same crop yields
that we got over the last four years
and just used current crop prices.
So, I took the national price index from last week.
So, $3.27 for corn, $8.11 for soybeans,
$4.63 for wheat, and $120 a ton for alfalfa.
And you can see with these more current
or realistic prices, that alfalfa treatment is still
the obvious winner in terms of average net returns per year
coming in at around $70 per acre per year.
And one of the reasons for this is that
in that corn following the alfalfa,
so we followed University of Minnesota recommendations
which says that you shouldn't need any additional
nitrogen application, which saves close to $100 per acre,
and that's one of the reasons why we saw
that better net return.
So, as we move forward in some of these
a little bit tighter system, where we're gonna
have to monitor some of these inputs,
certainly alfalfa could be a viable option.
And also if you're dealing with some
resistant populations, especially in soybean systems,
it's very difficult to control and it might be
increasing your production costs even further
in the soybean or corn systems.
So, really what it comes down to,
if you're someone who grows alfalfa
or some of your clients grow alfalfa,
you might want to think about planting it
in fields that you're trouble controlling weeds with.
It's more competitive, you have less reliance on herbicides.
But what if you don't grow alfalfa,
or what about the years where you're not in alfalfa?
Then what do you do?
So, I'll talk a little bit more about
emergence patterns and how you can
maybe change your timing of some of your
field operations to try and improve control.
So, basically in the same study,
we documented the emergence timing, as well.
And across all the treatments, this shows you
basically what giant ragweed emergence looked like.
So, you have the date of the year on the x-axis
and then the percent emerged on the y-axis.
And where you see this arrow or the percentage
on the top of the bars just shows you
the cumulative emergence.
So, you can see, at least for giant ragweed,
it emerges very early, beginning of May,
peaks around the middle of May or towards the end,
then tapers off.
So, one of the things you can think about
in terms of improving control is
rather than having that early planting date
like you maybe would like to, think about
delaying planting even a couple weeks,
just to allow a little bit more of that giant ragweed
to come up, then if you're gonna go through
with a pass of tillage or a burndown application,
you can just hit more of those giant ragweed plants
that are emerging earlier.
And specific to tillage, there's really no effect
that tillage has on emergence, so it's not
gonna stimulate any additional emergence,
so you can feel pretty good about your control with tillage.
But then the other tradeoff is crop yield.
So, you wanna have an earlier planting date
so you can achieve your maximum crop yield,
so basically what this red line here that I just added
shows you the percentage of your maximum
soybean yield on average.
So, obviously, with your earlier planting date,
you're gonna achieve about 100 percent
of your yield potential, and as you delay
that planting date, you're gonna lose
some of that yield potential.
With the earlier planting date,
you might have a little more variability in that yield
just depending on weather events.
But, for the most part, that's when you're gonna see
your greatest yields.
And just to go through with that May 28th example,
so if you're gonna wait 'til May 28th
to go through with a pass of tillage before planting,
you're gonna get about 77 percent of the
giant ragweed is gonna be controlled with that tillage,
and you're only gonna lose about
eight percent of your crop yield.
So, just kinda start to weigh some of the
costs and benefits of some of this timing
or how timing can help you out a little bit.
Also, with a delayed planting date,
you're gonna have a little bit better crop emergence,
which is gonna allow that to be a little more
competitive with some of the weeds that you're dealing with.
So, now I'll start to summarize a little bit
and kind of bring this all together
with some of the other weeds that you might be dealing with.
So, what does this mean in terms of
integrated wheat management?
Well, I like to think of it kind of as
a game of percentages.
You know, how much do you want to rely on your herbicides.
As you may have seen some of the previous presentations,
as these weeds become more resistant,
those herbicides aren't gonna be as effective,
so you might not want to rely on those
quite as heavily as in the past.
So, just to continue and go through
the example I gave you before,
rather than having that earlier planting date,
even if you have a relatively effective Pre,
by the time that Pre wears off,
you're still gonna have quite a bit of ragweed to deal with,
or other weeds for that matter,
but if you think about delaying the planting
just a little bit, go through with a pass of tillage
or an effective burndown before planting,
by the time your Pre is wearing off,
you're only gonna have to deal with five to 10 percent
of the giant ragweed at least after that date in time.
And then in terms of your post-applications,
rather than having to follow that planting date
with an early post-pass, you can also delay
that post-application a little bit,
and you're gonna have to deal with less weeds,
and then they're probably gonna be more uniform in height,
so it's gonna be a little bit better control
with those later post-applications.
And also, certainly, if you want to incorporate
cultivation or some other practices,
they'd be effective, as well.
So, it's not quite that simple.
If everyone just had giant ragweed to deal with,
you probably wouldn't have jobs.
So, what does this mean with some of these other weeds?
So, just a couple other common ones,
like water hemp or lambsquarters,
so the shading here shows you kind of when
they're going to be emerging, and what this later
planting date might mean for some of these other weeds.
So now, those post applications that were delayed
might do a little bit better job on controlling
especially your late-emerging water hemp,
or maybe you later-emerging lambsquarters,
so they might be a little bit of more effective
on some of these other weed species.
Then also in terms of your Pre,
if you had that earlier planting date,
your Pre's probably not going to do a whole lot
on that late-emerging water hemp,
but if you delayed that date,
even a week or two, you're gonna extend that
residual activity a little bit longer,
it might get a little bit better control
for some of these other weeds, as well.
So, take home message: you can intensively manage,
prevent any weed seed inputs for two years,
at least with giant ragweed, you're gonna see
96 percent depletion.
And for some other weed species, it might be a little bit longer,
but certainly somewhere to start.
How do you maintain that?
Well, one mechanism is through crop rotation,
saw fewer weed escapes in the alfalfa.
There's less total emergence, and it's more competitive,
your harvest schedule's gonna eliminate
and seed production.
I didn't really talk about wheat much,
but you can use different sites of action,
specifically the growth regulators
that are more effective at controlling,
at least giant ragweed.
You could also alter planting date
in your corn and soybean systems, just even a week or so.
Maybe wait if you have one field that's really bad
with a certain weed, just leave that field
to last or something.
Even that extra few days can really
help improve control.
So, with that, hopefully I didn't go too far over.
Perfect.
- Any questions?
(applause)