Announcer: The following presentation
is part of the Agronomy and Horticulture Seminar Series
at the University of Nebraska, Lincoln.
-: Thanks, everyone for being here.
I'd like to welcome Dr. Andrew Kniss.
Dr. Andrew Kniss grew up on a corn,
dry bean, and sugarbeet farm in Bayard, Wyoming,
sorry, Nebraska.
Sorry, I'm getting confused now, Nebraska,
and that is about (indistinct) miles east of Scottsbluff.
It's the closest town to the Chimney Rock
if you're familiar with that going out there.
Andrew went and got his bachelor's degree
from the University of Wyoming
that's why I just got that mixed up.
And then went on to get a master's degree
under Bob Wilson with the University of Nebraska.
So he graduated from here in 2003,
and then went on to get a PhD at the University of Wyoming.
He's currently a professor, weed scientist
and the Department Head
of Plant Science at the University of Wyoming.
And I'll let him take over now.
-: I'm impressed Nevin got all the years right
'cause Nevin was one of my very first graduate students
and I have no idea what year he graduated.
So kudos on doing your homework, Dr. Lawrence.
So I've also learned while we get slides brought up here.
If there's any younger folk thinking about
trying to get back at their advisors
for all of the misery they put 'em through
during their graduate education,
one of the best ways to do that is become a collaborator
with your advisor after you start in your faculty position.
Because now, Dr. Lawrence comes up
with all these new fangled, crazy experimental designs
that I now have to implement as a collaborator
on some of his projects.
All right, so I am actually really kind of excited
to talk to you today.
So I'm gonna talk about a line of research
that I've been working on for quite a while.
Shortly after Nevin left actually,
is when we kind of started into this.
And it's about light and specifically reflected light.
And so the title of the talk,
what's light got to do with it?
Hopefully I will at least give
some indication of what that is.
So I'm gonna talk specifically about crop weed interactions
'cause I'm a weed scientist by training.
I like to really focus in on kind of how weeds and crops
are doing their thing in the field together,
how they interact.
I do have to give credit to the title though.
Tina helped me out with this,
what's light got to do, got to do with it?
So, I have to give her credit on that.
So, more seriously,
this is a figure that you would see
if you opened almost any weed science textbook, okay?
Where you will have on the y-axis, crop yield,
and on the x-axis, the duration of weed competition.
So how long weeds and crops are actually
in the same field together.
Basically, this is the reason why we control weeds, right?
So the longer the weeds are in that field,
the lower your crop yield is going to be over time.
So, not groundbreaking stuff here at all.
This is just really kind of basics.
So who wants to tell me,
thinking back to your weed science class, why this happens?
Why do we lose yield
as the weed stay in the field longer and longer?
It's not a trick question.
What's that?
There you go, competition.
Nutrients, water, and light, exactly on the slide, see?
It is not a trick question.
This is exactly what happens.
So plants are competing, right?
There's limited resources within any given.
This is basics of crop-weed ecology.
In any given area of land,
there's only so much nitrogen to go around.
There's only so much light to go around.
Light is actually one of the more limiting resources
in crop canopies, right?
Okay, so what we see then is at this point,
at some point you start seeing
the crop yield start decreasing from that horizontal,
because at some point
those weeds have used enough of that light or nitrogen,
or phosphorus, or water,
whatever the most limiting factor is.
At some point, the weeds start using enough of that
that the crop doesn't have enough
to produce its full yield potential, right?
Okay, what if I told you that everything you have been told
up to this point about weed-crop competition was a lie?
It's not, it's mostly true.
But I'm gonna try to spend the next little bit
basically making the case that what I just described,
isn't the whole story.
And not only is it not the whole story, in some cases,
what we just talked about
might not even be a majority of the story,
there might be more important things going on.
And so I want to acknowledge that I'm not the first person
to do this sort of work.
What I'm gonna be talking about mostly today,
is a phenomena called shade avoidance.
It's basically how plants respond
when they sense that there are other plants
in the environment to avoid getting shaded out.
So that body of work actually goes back to,
I think at least the early 1980s.
The first person that I'm aware of that started applying
shade avoidance research to crop-weed interactions,
is actually Dr. Clarence Swanton
from the University of Guelph.
There may have been someone before that
but that's the first that I'm aware of.
And this is the first paper that I read that kind of applied
some of these concepts to crop-weed interactions
written by Dr. Eric Page who I think is now with Ag Canada.
And so they actually were talking about,
does the shade avoidance response
contribute to basically the time
at which weeds are problematic in crop canopies?
And just to give you an example,
a statement directly from that early physiological changes
triggered by leaf reflected light, contribute to the onset
of critical time of weed removal.
So basically that reflected light
is a contributor to when we need to control weeds
before we start seeing that crop yield loss.
So that's kind of what got me interested in this.
And so shade avoidance might be super familiar
to those of you who are very plant physiological minded.
I'm gonna take a step back
and just kinda make sure everybody's on the same page.
I'm gonna explain this in a way
that even the soil scientists among us can understand, okay?
Just kidding, I have nothing against soil scientists.
So reflected light.
Okay, what am I talking when I say reflected light quality?
When we talk about light quality, we're usually talking
about the photosynthetic wavelengths, right?
Red and blue primarily.
And so if you look at what happens when sunlight,
having all the wavelengths of light bounces off a leaf,
what actually bounces off?
Which wavelength is reflected most?
-: Green. -: Green, right.
That's why we see it as green.
So this is actually a reflected spectrum
from a sugarbeet plant that we took
and you can see that major peak
right in that green wavelength.
So this is the visible spectrum.
So this is not all of what's going on.
So there's actually also outside the visible spectrum,
other wavelengths that are being reflected,
absorbed, all the same things.
And if you kind of extend that,
what you see is this other peak in the far-red spectrum.
Okay, so remote sensing folks will tell you
that that's where a lot of information exists
on how well watered the crop is, for example.
So plants are actually really good.
They've evolved the ability to basically change their growth
in response to this red to far-red ratio.
So it isn't just the absolute amount of red light,
it's not the absolute amount of far-red light.
It's the ratio of those two.
So, the red to far-red ratio, you might say
that this light drives the phytochrome reactions, see?
Back to Tina Turner.
And those phytochrome reactions are really important
for a lot of things in plants.
So if you talk about trying to get plants to flower,
it's not only day length,
it's also this red to far-red ratio.
Seed germination is controlled by this red to far-red ratio.
There's a lot of things that are controlled within the plant
in this red to far-red ratio
or due to this red to far-red ratio,
including the shade avoidance responses.
And so that's what we're gonna talk about.
So this figure, I blatantly ripped off,
not from Tina Turner, but from Clarence Swanton,
he actually has this photo on, I think, Syngenta website,
basically illustrating what's going on.
So if you think of a corn crop, they've got this top photo
or this top image where you don't have weeds there.
So that reflected light is not going to be enriched
in that far-red spectrum.
But if you have this corn crop growing in a weedy field,
then this reflected light bouncing back up to that corn crop
is going to be enriched in that far-red light.
And so these two plants are going to grow differently.
And the primary things
that we talk about most in shade avoidance,
is that this corn plant tends to devote more resources
to growing tall.
And usually it does that at the expense of the root system.
And that's because if it's growing
in that perceived competitive environment,
that corn plant knows
as much as the corn plant can know anything,
that corn plant knows
that it's going to be limited for light soon
because it's got all these weed neighbors.
So, Clarence and his group actually developed
a method to look at that.
So if you think about these images on the left,
the ones on the right are actually
how they ran some of their studies,
where they have separate pots,
just completely different resource pools.
So there's never any direct shading,
there's never any competition
'cause the root systems are in different pots
and they can actually observe those differences occur
in that system.
So if you look at the list of responses
that have been attributed over the years
in the pretty large body of research on shade avoidance,
there's a whole bunch of things
related to, again, primarily trying to grow tall
at the expense of other things.
And so reduced branching
is one that they've seen in soybeans,
which can be really challenging or yield potential.
If you have fewer branches, you have probably fewer nodes,
fewer flowers, fewer pods.
Same thing in corn, if you basically delay that maturity,
it produces fewer kernels.
I'm mostly interested in some of these that relate to roots,
which I'll talk about in a little bit,
but there's a whole bunch of things.
And depending on the crop plant you're thinking about,
almost all of these relate to at least
some yield component in some crop,
leaves for forage crops, stems for maybe some fiber crops.
You've got the roots for root crops, seeds.
So a lot of these things are yield relevant
when we talk about the effects of shade avoidance.
And so what I'm gonna go through first
is really where we started on this project
primarily looking at sugarbeet
because as far as I could tell,
no one had really looked at shade avoidance
in an agronomic crop
where root is the primary economic product.
And if root to shoot ratio is usually what's being driven
by the shade avoidance responses,
it seems like that's a really important thing
that we should understand better.
So that's the primary thing.
But the other thing that made sugarbeet
kind of an interesting crop
is it's a biennial species that's harvested as an annual.
So there's really nothing in the literature
about shade avoidance responses in biennial species.
It also can't grow tall.
Anybody that has walked through a sugarbeet fields,
know that if knee high, you gotta really tall crop.
So how does a crop that can't grow tall,
respond to these shade avoidance triggers?
Because normally corn, beans, all these other crops
are trying to grow tall, sugarbeets can't do that.
So that's kinda why
we started looking at this in sugarbeet.
And I do want to make sure
that I acknowledge more than just Tina Turner.
I wanna acknowledge all of the graduate students who've done
most of the work
and actually been involved in the project from the get go.
Louise Lorent, Tom Schambow, Albert Adjesiwor,
and my current PhD student, Joe Ballinger,
have all been doing shade avoidance work in sugarbeet
and have been the primary drivers
behind all of the work
that I'm gonna show you getting done today.
Okay, so I'm not gonna spend a lot of time on the methods
other than to say we planted a lot of sugarbeets
in a lot of buckets.
That's pretty much what it boils down to.
Within any given study that I'm gonna show you,
we had at least 15 reps
because one of the primary differences
between sugarbeet and crops
that I think more researchers are more interested in
like corn and soybeans,
sugarbeets have a lot of inherent variability.
Just from plant to plant, there's a lot of variability
so we need to have 15 to 20 individual plants as a replicate
in order to find anything from a statistical standpoint
because there's a lot of plant to plant variability
and how they respond to anything.
And the first bit I'm gonna show you is two treatments,
which is grass versus no grass.
And I'll show you what that means in a minute.
And I'm also gonna show you a little bit of data
comparing sugarbeet, table beet and Swiss chard.
And I'll explain why that's interesting
here in a little bit.
Okay, so the key thing, if you ignore the next,
kind of tune out the next four or five minutes,
just know that all of the treatments that you're seeing
have adequate nutrients and water, no direct shading.
So again, very similar to the way
Swanton set up his studies.
We wanted to make sure that the sugarbeets
and the surrounding grass species
were not competing for the same pools of resources.
So we wanted to limit their interactions
to just that reflected light.
And I guess if you wanna get really technical,
they also might have been responding to like volatile
organic compounds and other things.
But generally speaking,
we're attributing almost all of the things that we've seen
to the reflected light.
So, we started with these 19 liter pales,
which is extremely similar to a five gallon bucket,
if you're interested.
We created cardboard mailing tubes about four inches tall
and then we taped plastic around that.
And then we set that into the bucket.
And so what that allowed us to do then,
is we could plant the sugarbeet into that center ring
once we filled it up
and then it would have the whole bucket to spread its roots.
And then we would plant the grass and the grass treatments
on top of that plastic.
So again, the root treatments
were never actually allowed to interact,
they were not interacting for the same pools of resources.
So we filled all that up with potting media,
soil scientists get really mad when I call it soil,
with potting media, planted sugarbeet in the middle.
In the soil treatments it looked like this
and in the grass treatments it looked like this.
So that's the general setup for all of the research
I'm gonna be presenting related to these sugarbeet studies.
This figure is mostly a plug.
If you have a research project that you want to show
how things work in a really simple diagram,
find yourself a graphic designer who can draw it up for you.
We got so many questions on these methods
every time we went to publication,
every time we presented this work
and I had a friend of mine, who's a graphic designer,
Jessica Perry, draw this.
We never got questions about that again.
It was just so clear and obvious once people can see this.
So hire yourselves a good graphic designer,
pay them what they're worth.
Okay, so one of the most consistent things we saw
across all of the studies.
And so the main one I'm gonna show you
and then I probably won't show you
a similar data on this again,
is that the number of leaves over time in sugarbeet
was dramatically reduced
where it was growing surrounded by grass.
So the grass treatment on average in this particular study
was producing about 12 leaves.
Where the sugarbeet was growing
without that grass surrounding it,
it was producing about 25 leaves by the end.
So a pretty major difference.
And that was by far the most consistent thing.
Year to year
the leaf numbers have been really, really consistent
in terms of differences between the two species.
So in this first set of studies
where we're just looking at season-long competition,
the root weight, which again, for sugarbeet
is the economic product, we observed about a 70% reduction
in root mass just by having that grass growing nearby.
So, a pretty dramatic change in the economic product
again, just due to shade avoidance,
not due to actual resource depletion.
Now, here's where that table beet, sugarbeet,
Swiss chard thing comes in handy.
Anyone know what the species is for sugarbeet?
Beta vulgaris.
What's the species for table beet?
(audience speaking indistinctly)
-: What's the species for Swiss chard?
The miracles of plant breeding,
all three of these are Beta vulgaris.
And so we thought it'd be kind of interesting to see,
okay, we've seen this in sugarbeet,
we know what happens there.
How does table beet, which kind of similar
in form and function respond
and how does that compare to Swiss chard,
which actually has a fibrous root system
and is grown as a leafy vegetable?
And what we saw is basically they all do the same thing.
So this is not something
that we've kind of bred into sugarbeet,
this is something that kind of exists
throughout the species.
So again, this is the sugarbeet data,
looking at the leaf area, leaf biomass, and root biomass.
We saw that the grass treatment reduced all three.
Table beets, almost the exact same trends,
a little bit difference in magnitude here and there,
but huge reductions in all three.
And in the Swiss chard, we're going to assume
the root biomass also, but it turns out washing
a fibrous root system out of that potting media
was a disaster mess and we didn't even try it
after we did the first three or four.
But if you look at the leaf area and leaf biomass,
exact same trends.
And so we probably assumed that the roots probably
did the exact same thing also
but we didn't actually quantify that.
So again, about a 70% reduction in the economic product
in those two species where it's roots.
Again, we know that roots,
plants kind of give up on those roots
to try and grow taller.
Okay, it turns out, though, in sugarbeets,
they don't actually grow taller
because, again, they don't have the ability to grow taller.
One of the things that I learned about myself
during the many years we've been doing this project is,
I don't trust any data that looks kind of exciting
and new and interesting.
So, we did that in the buckets
and I was like, 70% is too big.
There's no way that can be real.
So then we did a greenhouse study
and we saw about 70% reduction.
Well, that can't be real.
So then we did it in the field
using citing and grass as kind of a different method,
seeing almost the exact result.
I'm finally convinced about 10 to 12 years
after kind of doing this line of research,
I'm pretty sure it's real at this point.
I do think what we're seeing is real.
So again, the most consistent thing we saw in sugarbeets
due to shade avoidance mechanism,
is that slowed leaf appearance rate.
So the leaves just appear
at a much lower rate during the growing season.
We assume that that then kind of has
the knock on effect of if you have fewer leaves,
then obviously you're gonna have reduced leaf area.
That's not a one to one relationship, but it seems like
it happened pretty consistently in our studies.
And if you don't have leaves to photosynthesize,
you end up with that reduced root weight.
So we kind of feel like that's probably
the progression that's going on in the plant
although we haven't really,
I guess, identified that for certain.
But those three things,
we are convinced are real effects that happen
pretty consistently
when you have season-long shade avoidance
occurring in sugarbeet.
So obviously the question then
as a weed scientist in particular,
but also the growers that we would present this data to,
is what happens if we control the weeds?
Because growers, it turns out,
are a lot smarter than their weed scientists friends.
They actually go out and kill those weeds
instead of just letting them stay there all year long.
So our question then is,
well, what happens if you control the weeds?
Do we see similar things?
And it turns out weed control in our experimental system
is super easy, we just go pull out the grass ring.
So you take out that side,
you fill it with soil and water,
you've got 100% weed control immediately.
So we can put grass in,
take grass out at any point during the growing season
and we can then just have that present for different times
during that sugarbeet's life.
So we did--
(audience speaking indistinctly)
We get that question a lot also and it turns out it depends.
So again, we didn't leave it just white,
we would put soil or potting media in there
so that it was more typical to a soil.
We have actually measured the mulch question.
And mulch responds very similarly to soil
because if you don't have the green, the active chlorophyll,
you don't see that bump in the far-red spectrum.
So we did what most weed scientists will recognize
as a critical period study.
So basically, we have early season removal series
where we have both ends of the spectrum,
where we have a treatment
where we have no weeds season-long
and at the other end we have a treatment that has weeds
throughout the entire crop life cycle.
And then we have,
the green bars represent when weeds are present.
So basically we have then when you control the weeds.
So this one, we control the weeds
at the two true-leaf growth stage.
We control them at 200 growing degree days,
after that, 400 growing degree days after
and then the full season.
So basically when should you control weeds
to avoid these responses?
And then we also have the late season addition series.
So here you assume that you keep it weed-free season-long.
The next treatment you allow the weeds to show up
at 400 growing degree days after planning,
200, 100, two true-leaf stage.
So I'm gonna show you the data
in both of these two series.
So the early season presence,
and then the late season addition.
And this is what that data looks like.
I'll give you two seconds to make sure everybody gets
all the information that you need.
One of the things that you'll see is,
the individual plant differences
that we see from year to year.
And I know like soybean breeders and corn breeders,
their heads are exploding right now
looking at the amount of variability we have plant to plant.
So I'm not expecting you to know what that is.
So I'm gonna walk you through each of the steps.
So I'm gonna start with the late season edition
because this one, frankly,
I think is more in line with what we expected to see.
Okay, so the way you interpret this figure,
on the far left is where we had weeds present
the entire season.
So, basically if you think of the start
of the weedy treatment at planting
and then let to go for the whole season.
And at the other end of that
is the season-long weed-free treatment, okay?
So that's like if you were to start the weeds
on the day after you harvested, okay?
So basically effectively, no weeds.
And that's basically then the trend that we observed
that the longer weeds were in that system,
and I'm saying weeds, but I actually mean the turf ring,
Kentucky bluegrass, for those interested.
The longer that turf was in that system,
the more yield loss we observe.
So our first treatment as I mentioned earlier
was the two true-leaf beets.
That's the earliest timing
at which we basically allowed weeds to start growing.
And if you actually look at that, just as a reference,
'cause two true-leaf sugarbeets is a really common time
for most goers to go out and spray weeds.
And so if we use that kind of a reference,
which doesn't make as much sense in this context,
but will on the next slide,
we observed about a 22% yield reduction if weeds came up
at the two true-leaf stage
and then competed all the way to harvest, okay?
So now let's look at the early season removal timing.
So this one, if you think about the control treatments,
they're flip flopped.
So this now on the left side is the weed-free treatment.
That's where weeds were never present
and at the other side,
you've got the season-long treatment.
And then this, again, is gonna be the two true-leaf weeds.
So basically, if you controlled
two true-leaf beets
or controlled weeds of two true-leaf weeds
up through season-long,
we actually don't see any trend there whatsoever.
So there's no difference between having season-long weeds
and having weeds basically between planting
and the two true-leaf beets.
If you have weeds present for that first two to three weeks
of the sugarbeets life cycle,
you end up with the same yield potential
due to shade avoidance.
Again, not due to overall competition,
but due to shade avoidance
as if you have weeds in there the entire season.
The difference between the weed-free treatment
and the treatment where we remove weeds
at the two true-leaf stage, is a 31% yield reduction.
So we know and have known for a long time
that early season
weed control in sugarbeets is really important
as it is for most crops.
I think we've probably underappreciated
why it's so important
and I think this probably is a major driver.
So if you think of this just kind of on a timeframe,
that time period between sugarbeet emergence
and the two true-leaf stage,
having weeds present for that period,
cause about 30% yield loss.
If weeds come up at the two true-leaf stage
and compete all the way until harvest,
that period of time even though it's much longer
during the crop growth cycle,
that's only worth about 22% in yield potential.
So way more important to keep weeds out of the system
during that early stages of sugarbeet growth.
Again, just due to shade avoidance.
If you actually allow competition,
we've done a little bit work on that front too,
these numbers definitely change
but it never really minimizes
the importance that that shade avoidance is contributing
to that early season part.
Okay, so the nutshell kind of practical implications of this
is what we call starting clean
or planting your crop into a weed-free area
is really important, okay?
So we don't want the sugarbeet emerging into a weedy area
or we're basically setting ourselves up
for a pretty major loss in yield right off the bat.
So how do we control early season weeds in sugarbeet then?
Is the next practical question that we've got.
I'm going to talk a little bit about
a particular weed that is near and dear to my heart
and that's kochia, scientific name Bassia scoparia
for those of you who may be interested,
mostly because it's one of the earliest weeds to come up
in Western Nebraska, Eastern Wyoming, Colorado area.
If you actually look at the optimal
germination temperature in Plata
compared to other weeds that we have in that area,
it has among the lowest thermal requirements
for germination.
I actually have a thermo gradient table in my lab.
We've done studies where we run
basically from zero up to 30 degrees Celsius.
Kochia is the only species I've seen
where you can have ice on part of the filter paper
and a kochia germinating on the other half.
So it won't germinate at zero degree C as far as I can tell,
but really, really close.
So you don't have to accumulate very many heat units
before kochia will germinate.
So it is the early season weed
that I'm gonna talk about most.
So this is what kochia looks like
for those of you who may be unfamiliar
'cause I know it's a lot less common
when you get clear over to this side of the state.
In sugarbeet, kochia is one of the most
economically damaging weeds.
So there's been a lot of data looking at the yield impacts,
about one kochia plant per 10 meters of sugarbeet row,
usually grown in 30-inch rows in the region,
will cause about a 10% yield loss in sugarbeet.
So really a highly competitive weed
probably involved in some way, shape or form
in that shade avoidance response as well.
Okay, so when we talk about starting clean in most crops,
one of the things we're talking about
is pre-emergence herbicides, okay?
So basically burn down if you're in a no-till system,
but also some sort of a herbicide with residual activity
to control those early emerging weeds.
It turns out in sugarbeet, we don't really have that.
We have currently zero effective herbicide options
for kochia control,
especially if we have glyphosate resistant kochia.
Glyphosate is the only post emergence tool that we have
that is effective for controlling weeds in sugarbeet.
So this is actually some study I did
with Nevin's predecessor, Bob Wilson in Scottsbluff
in addition to Phil Stallman at Kansas,
Phil Wester at Colorado, and Mike Nigg in South Dakota
back in 2010, 2011,
where we actually looked at how are we gonna control kochia
without glyphosate?
So this is just as glyphosate resistant kochia
was starting to show up in Western Kansas
and hadn't really spread to most other places yet.
But we wanted to know, "Okay, if we don't have glyphosate,
how are we gonna control it?"
So the way we did this study is we actually chose
what we felt were probably the top three herbicide programs
within each crop where kochia is a problem in the region.
So we have in corn,
we got really good kochia control.
We don't need roundup in corn, right?
In soybean, we got really good kochia control.
We didn't really need glyphosate in soybean.
In fallow, a little bit less.
We had a few stragglers.
But overall, we're still getting
over 95% control in most scenarios.
Wheat, about 90 so a fewer options.
And then we've got sugarbeet,
where a median kochia control in sugarbeet
with our three best options were about 40% kochia control.
So we just don't have,
in fact, this weed, kochia,
is one of the reasons we saw such rapid adoption
of Roundup Ready sugarbeet in the region
is because we didn't really have the ability
to control this weed,
Roundup Ready sugarbeet gave us that tool of glyphosate,
we could control it,
now that we're seeing glyphosate resistance,
we've lost the ability to control that weed again.
Okay, so obviously the answer to this question, then,
is cover crops, right?
We don't have any herbicides,
we've gotta control kochia, cover crops is the solution.
I want to give another shout out,
not to Tina Turner this time,
but to one of my favorite philosophers of all time,
Mr. Homer J. Simpson.
He said this about alcohol,
but I actually like applying it to cover crops.
"The cause of and solution to,
all of agriculture's problems."
And I'll tell you what I mean there in a little bit.
So we know that a good cover crop
can provide good weed suppression if it's managed correctly
for high biomass early enough in the season.
But it turns out if you have a cover crop
that is producing lots of biomass early in the season,
does the sugarbeet know that that's a cover crop or a weed?
No, so it's gonna drive the exact same response.
And in fact, none of the bucket studies I've showed you
had anything to do with weeds, right?
It was basically more similar to a cover crop
than it would be to a weed canopy
because we were using Kentucky bluegrass turf.
So a good solid cover crop
that's gonna provide weed suppression if we plant green,
which is how we are likely to get most
of that early season weed control
is gonna cause that same sort of shade avoidance effect.
Okay, so we can delay the termination or we can apply early,
but the earlier you terminate the cover crop,
the less likely it is you're gonna get
that weed suppressive effect, okay?
And I'll talk about why that is here in a little bit.
One of the questions that I had then is,
what if we break out the old band sprayers
that we used to use in sugarbeet?
So those of you who are unfamiliar with band sprayers,
basically we can apply herbicide in a relatively narrow band
just right around the sugarbeet row, keep it weed-free,
and then we can allow things in between
to grow a little bit more.
So the idea here is can we provide a cover crop-free band
with herbicides that is wide enough
to avoid that negative impact on the crop,
not induce those shade avoidance responses,
but narrow enough that it still might produce
some weed suppression
if we let it grow a little bit further on into the season?
So we did this study at Sheridan.
Again, I'm not gonna spend a lot of time on the methods,
but we basically designed a little
individual row band-sprayer.
So had bicycle,
or actually this one wasn't the bicycle wheels,
they actually had to hand hold it.
And it was kind of a pain, but they did a good job.
And you can see that we basically applied
different size band over that
and sprayed out the winter wheat
and then right over top of the crop row.
And those bands were different sizes
ranging from nine centimeters wide
up to 76 centimeters wide,
which the 76 is just a broadcast application
because sugarbeets are planted in 76 centimeters row,
which is 30-inch rows
for those of you that are not metrically minded.
Okay, so what we measured here is soil moisture
in the sugarbeet row, then stand counts.
We actually measured chlorophyll
because chlorophyll reduction
is actually a really widely agreed upon impact
of shade avoidance responses
as it reduces the chlorophyll concentration in leaves.
So we wanted to see if that had any impact.
Then we did leaf biomass and root biomass.
Okay, I'm not gonna get into a whole lot of details here
other than what I'm gonna show you is we fit a model
that has a right side asymptote to all this data.
And if you look at basically the bandwidth
that gets about 95% of the way up to that asymptote,
we can use that as more or less a bandwidth
where we're minimizing the impact on the crop, okay?
So that's all you need to know for that.
So what did we find?
I'm gonna show you stand loss first.
So again, over on the right side,
that asymptote we can assume is what happens
in the absence of a cover crop.
That's just broadcast applied herbicide
where there's no green
until you get to the next sugarbeet row.
And so as you go further and further left,
if we draw a line
at where that line basically gets to 95% of the asymptote,
that's what I'm gonna call anything to the right of this,
any bandwidth greater than that
is probably gonna have minimal
at least less than 5% impact on the crop.
So this one actually surprised me.
So this is actually sugarbeet stand.
The narrow bands actually reduced sugarbeet stand,
which I did not expect
'cause nothing in the shade avoidance literature
prepared me to think that we would actually reduce
the number of sugarbeets.
So, I still remain a little bit skeptical of that.
The primary explanation that I assumed
probably made the most sense was,
well, the cover crop here is not just shade avoidance.
It's actual competition.
It's probably drying out the soil and we're getting reduced
or stressed emergence, something related to that.
However, that's not well supported by the data.
We actually collected soil moisture.
We collected soil, did volumetric water content.
We didn't really see any trend whatsoever,
even in those narrow rows to reduce the soil moisture.
And we were taking these samples
just before the next irrigation
when the soil was theoretically as dry
as it was going to get before we irrigated again.
And so we did not see that we were having much of an impact
in that top two inches of soil.
So I don't think water is explaining
the standard action that I showed you on the last slide,
but I don't know what is to be honest.
So this is still kind of a mystery to me.
We haven't had an opportunity to repeat this study yet.
(audience speaking indistinctly)
We did not look for allelopathic effects.
I am happy to pontificate later
about my opinion of allelopathy,
but yeah, we did not look at that.
It could certainly be playing some role here.
So leaf dry mass per plant
and then I'll show you root dry mass per plant.
Here, again, to get to that right side asymptote,
you needed a bandwidth of about 49 centimeters
in a 76-centimeter row and for root biomass,
so yield in a sugarbeet crop,
you need a cover crop-free band of about 51 centimeters
in order to basically negate the negative impact on the crop
from having that cover crop present.
Chlorophyll, which again,
is one that I'm super interested in,
not entirely relevant to crop yield,
but certainly is an indicator
of the crop responding physiologically
in some way, shape or form.
The ED95 was actually greater than 76,
which doesn't make any sense
but what it is telling us is that really,
there is no bandwidth that you can have a cover crop
where you're not gonna have some impact.
So even as far as up to that 76
or at least past this 43 or whatever it was centimeter,
the sugarbeets can sense
that there's something going on out there.
So in terms of that distance
to where the sugarbeet can tell there's plants growing,
it's probably going pretty darn close
to the next sugarbeet row.
Okay, so the cover crop-free band required
to minimize the effect on sugarbeets.
Again, for stand you can get away
with about a nine-inch band and 30-inch rows,
but for leaf biomass and root biomass,
you need about a 20-inch band and 30-inch rows
in order to make sure you're not negatively impacting
the crop with that cover crop presence.
So getting back to the two questions
that kind of drove this study,
can we provide a cover crop-free band
that is wide enough to avoid negative crop impacts?
Yeah, I'd say if we get into that 20-inch area,
50 centimeters, we're not negatively impacting yield.
And so I would say from an agronomic perspective,
even if we're reducing chlorophyll a little bit,
if we're not reducing yield, fine.
Go ahead and do that.
Is that narrow enough to provide useful weed suppression?
I don't know that I'm buying that.
You can have a hell of a lot of weeds
in a 20-inch band around a crop row.
And so in terms of season-long presence,
I would say this probably isn't a very good solution.
Now, the logical next step of this is what happens
if you terminate it after that two true-leaf stage?
There's still a whole bunch of research
that I think we need to do here to really tease out
how we might be able to implement
something like this in the real world.
But this is I feel like a pretty good starting point
and actually answers one of the questions
that we got a lot early on is,
how close do the weeds need to be to the crop?
This data suggests they can be quite a ways away
if that canopy is thick enough
and still have the shade avoidance effect being induced.
Okay, the last thread that I'm going to talk about,
and I'm gonna try and talk fast
to make sure I get done in time, will a green cover crop
suppress kochia germination?
So seed germination is a whole nother aspect
of not necessarily shade avoidance,
but reflected light quality and transmitted light quality
because in addition to the reflection,
if you look at what happens down at the bottom
of a crop canopy,
all the red light is being absorbed by the plants
because they're using that wave length for photosynthesis.
That far-red light
is being transmitted through to the ground.
And so if you're a seed at the bottom of that canopy,
you are experiencing a far-red enriched environment
or a relatively low red to far-red ratio.
That's one of the reasons
why cover crops work well for weed suppression
because far-red light inhibits seed germination.
And this is true in almost all of our agronomic weeds.
So if you have an environment
that is relatively low red to far-red ratio,
you're gonna have far fewer seedlings
germinating in that environment.
So you can actually induce this in the lab.
This is actually an extremely low tech seed lab
that we've got going on,
where we have two areas right next to each other.
One that we typically use in dark,
but we can also supplement it with red light,
blue light, green light, white light.
And then on the other side,
we can do basically the exact same thing,
but supplementing also with far-red light.
And so this would be an example.
We usually close the curtains
to kind of keep ambient light out,
but over here you'd have a dark scenario
and over here, you've got the, I think this is a red light.
The far-red light doesn't look very red
because again, it's mostly out of the spectrum.
So you get a little bit of bleed
into the red visible spectrum.
And this is what happens if you germinate most seeds
in a setup like that.
So lettuce is kind of our crop species that we use
for kind of our standard control between experiments
because lettuce is just like always responds the same.
Doesn't matter about what's going on,
ambient temperature or anything else.
We know that it will germinate pretty well
in red light or in darkness
and we know that lettuce will not germinate
if there's far-red light present, okay?
And this is actually really true of a lot of species.
So the dark and the red can change depending on the species.
So lamb's quarters, for example, lamb's quarters
will also not germinate very well in the dark.
So it won't germinate well in the dark,
it won't germinate well in far-red light,
it'll germinate really well in red light or white light.
So how does kochia respond?
Well, most species, again, are suppressed by far-red light.
Kochia does not care about your rules.
Kochia will not germinate if you don't have water.
And that's pretty much it.
If you give kochia water,
it doesn't care about the temperature,
it doesn't care about the light environment,
it doesn't care about literally anything else.
If that seed is viable and it imbibes,
it is going to germinate.
And so this is really
kind of disappointing to me as a weed scientist,
thinking, well, we can potentially use cover crops
to suppress some of the germination
because kochia is actually
a really short-lived seed in the seed bank.
Three to four years later,
almost all the kochia seed is dead.
But my guess is from an ecological standpoint,
that's probably why it doesn't give a shit
what the light environment is.
"I'm gonna be dead next year, I'm growing."
And that's probably what's going on here
is it has evolved the ability
to just be totally far-red light insensitive
because this is the one shot it's gonna get
to actually produce seed.
Really disappointing from an agronomic perspective though,
because we're probably not gonna have a whole lot of impact
by trying to suppress germination.
So we actually probably
need to be thinking about the other way,
how do we get more of it to germinate early enough
so we can kill it before we establish the crop
because this method is probably
not going to be super effective.
So I'm gonna skip right over this
because there's a whole bunch of stuff
that we're still trying to look at,
but I do wanna acknowledge all of the other people
who have helped me out on this line of research,
a bunch of graduate students and others,
technicians, cartoon characters and rock singers.
Wanna acknowledge the Department of Plant Sciences,
the Ag Experiment Station, Western Sugar,
who actually funded a lot of the work you just saw.
And the USDA NIFA, which funded
a whole bunch of the rest of the work.
So I do wanna thank everyone for coming
and for being present for the talk.
I'm happy to answer any questions if there's time
and if you are interested.
So thank you very much.
And I also won't be offended
if you all just leave immediately and run away.
I believe they're the same thing.
I think it's just where the terms originated.
Red to far-red has always been used
in the plant ecology literature
and they're pretty narrow in just the wavelengths
that are absorbed by the phytochrome.
So, like red is 680,
not like a range that we would normally think about red
or that a remote sensor might think about red.
Far-red, I think is 740
whereas near infrared is usually explaining
a pretty wide band past that red.
Far-red, you could say the same,
it's a lot of things, but yeah.
It's usually just how it's defined in the origin.
Yes, yes, timing can be important in far-red sensitivity.
And in fact, one of the students,
there's a whole bunch of stuff we've done that was outside
the scope of what I could fit in a 50-minute talk,
Albert Adjesiwor who's now at the University of Idaho,
actually had done some work on the end of day far-red, yeah.
Because in the mornings and evenings,
and actually if you think about even our experimental setup,
in the mornings and evenings,
you tend to have a light environment
that is more enriched in far-red light
partially due to the environment
but also partially if you think about the sun angle.
Even if the grass is not above the sugarbeet,
when the sun is coming in flat,
it's going to be getting more of that far-red
compared to a more upright angle.
So yes, end of day far-red light
is actually one of the things that had been heavily studied
in terms of shade avoidance.
That's one of the things that drives flowering cycles,
is end of day far-red light.
And Albert has actually done some of the work
to see how it compares to that.
Google him and give him a call
if you're interested to discuss that
because he actually has looked at a little bit of that.
But the timing of the far-red light does make a difference.
Speaker: Talk about the angles.
-: Yeah, so the question is how does leaf architecture
impact the results generally speaking?
So graph that we use does have a relatively
upright leaf architecture.
But the reason we chose it
isn't necessarily due to the leaf angle,
but just that it creates a mat of a crap ton of green.
That's really what we were shooting for.
So Albert actually also had done some work
on kin recognition, which I'm not gonna get into today,
but basically do all plants show the same response?
And so he used different plant canopies,
some broad leafs, some grasses.
And at least as far as sugarbeet is concerned,
it tends to not matter.
As long as you're reflecting far-red,
it doesn't matter what the species is
that's reflecting it to it, it's responding the same way.
That's not always the case though.
There are some species that will respond differently
depending on if it's a grass versus a broad leaf
or a closely related plant versus a distantly related plant.
So I don't know if those are light quality-driven
or something else going on,
but at least in terms of leaf architecture,
we did not see any impact on how that would affect
the sugarbeet growing.
It kind of responded the same
regardless of what the species growing around it was.
Did we try to simulate the reflectance color without plants?
Yes and no.
So actually that first paper
when Louise and Tom were doing this in the very early days,
we actually weren't using weeds,
we were using different colored plastic mulches.
And we got a lot of different reflectance spectrum
because one of the things
that I have always been skeptical of
it was whether far-red was really required.
'Cause it seems to me that plants are reflecting
a crap ton of green light,
why wouldn't they just respond to green light?
That seems easier to me.
But no, green reflectance,
we had multiple different colors of green,
really didn't see any changes in the plant from those.
So it really is that far-red light.
So we have not been able to find a plastic tarp
that is a very good reflector of that far-red spectrum,
but we have replicated the results
by basically using overhead far-red lambs.
So basically similar to what we did
in the seed germination studies,
some of the end of day stuff
that Albert was doing in the greenhouse was basically
shining that far-red light from the side in the greenhouse
and it would elicit a similar response.
It wasn't quite as dramatic, but basically the same thing.
Yes, are there opportunities
to trick weed seeds into germinating?
Yes, I keep mentioning Albert Adjesiwor.
You're like just totally asking all the questions
that he has already asked or is in the process of asking.
So at Idaho, one of the things he's looking at
is can we use some sort of an implement
that you hook on a tractor?
Or when we had discussed it, like a side roll sprinkler
that basically just shines a bright ass red light
down on the ground to try and stimulate seed germination,
do that or hook it up to a shallow tillage implement
and kind of blow red light trying to get them to germinate.
And it turns out it doesn't require
a very large burst of far-red light
to get some weed seeds to germinate.
And so we actually do feel
like there might be some potential
to use that in a field type setting,
burst red light, get them to grow,
spray them out or till them out,
kind of a stale seed bed approach
that organic weed managers use
but in a way that tries to get more of them to germinate
so you can kill 'em before you establish your crop.
So we have looked a little bit of that.
We think there's promise there,
but we're probably a long ways
from being able to operationalize it.
I guess, to repeat the question for those online,
won't we eventually see resistance
to any kind of light mediated control strategies?
And I guarantee we will.
I think if there's anything we've learned
in weed science over the last 50 years
is that no matter what we do,
if it's effective at controlling weeds,
we will select for the weeds
that it is not effective against.
So, yeah, because there's already preexisting differences
between species and sometimes within species
on how sensitive they are to far-red light,
if we start implementing that for control,
we will see differences.
And in fact, one of the things we know
in common lamb's quarters, for example,
that the far-red dependency decreases over time.
So, a old common lamb's quarter seed that's 20 years old,
is way less sensitive to far-red light
and is more likely to germinate
in the presence of far-red light
compared to a common lamb's quarter seed
that is two years old.
And again, I think probably that evolutionary like,
you're getting to the end of life,
man, this is your last chance.
So, yeah, I think we'll probably
select for different age structures of seed banks
and also we'll probably eventually select for biotypes
that have either more sensitivity or less sensitivity
depending on what we're using for control.
What does cloud cover do to the wavelengths coming in?
I do not know the answer to that one.
Here I thought I was totally prepared
for all the possible questions
as many times as I've presented.
I have no idea, I would not expect cloud cover
to be a major inhibitor of either of those wavelengths,
at least not selectively so but that's pure speculation.
So I'll probably have to do some research on that.
Well, thank you very much.
(audience applauding)