- [Voiceover] It's my pleasure and honor
to introduce Dr. Mark Renz,
an extension weed specialist here
at the University of Wisconsin, Madison.
He does most of his research in
the biology and management of weeds
in perennial cropping systems and natural areas.
Mark has over 15 years of experience
conducting weed management research
throughout the United States.
With that please help me welcome Dr. Renz.
(audience applause)
- Thanks Jeff.
It's a pleasure to be here today.
I have two goals in this session, in this presentation.
The first and most important is to get
you out early so you can get in the front of the lunch line,
cuz i'm sure it will be a long one.
And then the second, I wanna just talk about
when we're developing weed management
and utilizing a burndown program,
some simple concepts that you can utilize
to potentially improve control,
particularly with some of your perennial weeds
that you have in that system.
But first let's talk about why do we do
burndown treatments?
What's the ultimate goal?
I have several split up here,
but I want to emphasize the number one goal
of our burndown treatments is what?
It's simply to prevent that early season competition
during that crop emergence and establishment.
Just remember that.
I think in general we do a pretty good job
with our burndown treatments
in accomplishing that one goal.
But there are also some opportunities to get
some enhanced weed control,
some of it will come at an additional cost,
from our burndown treatments.
Some of those additional benefits may be
some additional weed management.
We can use some herbicides in our burndown treatment
that have residual activity that can delay weed development,
that can particularly allow us to delay some of our
post herbicide applications,
and maybe reduce some of our weed population densities.
From a weed perspective, some of our opportunities
really are to
this is an opportunity to reduce and manage
some of our weed populations.
Now I was tasked with focusing
on perennial weed management,
how we can increase some of our weed management
on perennial weeds with our burndown treatments.
But I'm also briefly and initially gonna talk
about winter annual weeds.
So why did I change and add this topic
on to our system?
Well, I want to first remind you guys
what a winter annual weed is.
A winter annual weed is one that is gonna germinate
in fall to the early winter.
What's gonna happen is, when springtime hits
and everything gets going,
those are gonna be really widespread, flowering
and very troublesome and very competitive.
And here's a great picture
that was taken by Jerry Dahl showing in early May,
we can have a carpet of weeds
that can be extremely, extremely competitive.
Well, why am I talking about winter annual weeds
when the title has perennial weeds in here?
Because I expect large populations this spring.
Remember how nice and pleasant it was in October?
Well, what happened during that time frame
is many of those winter annual weeds
I would have expect have germinated
and developed pretty actively.
We have a nice snow cover throughout much,
if not all, of the state.
They're likely overwintering well,
and I expect bumper crops
that we're gonna have to deal with in spring,
so I want to bring that to your attention.
What are some of these culprits?
Chickweed species are some of those you need to be aware of.
We have two main species,
although there's several in Wisconsin,
Mouse-eared and common chickweed.
Prostrate growth, opposite leaves.
The mouse-ear can be very hairy
while the other chickweed species are not as hairy.
Fairly easy to identify with the white flower.
Really be on the lookout for this one.
Shepherd's purse, this is one over the last 10 years
I've seen really rapidly expanding throughout Wisconsin
in many of our no tell fields.
Easy to identify.
When it's flowering it has those heart shaped fruits
that are present, white flowers.
But also we'll see this right when the snow melts.
It'll be growing right away and have highly divided leaves.
It's easy to identify as well.
Finally, the third one I want you to be
on the lookout for is pennycress.
Some may refer to this as a crop.
I would not call this a crop.
I would definitely call this a large problem
and a weedy species, and I expect lots of it.
Easy to identify by having these wavy
to serrated leaves that clasp the stem.
If you crush it, it has a very bitter smell.
Some say it's garlicky.
And clearly easy to identify when it has fruit present
because those fruits have that clear dime shaped
fruits that have a notch in the tip of them.
Just be on the lookout for those three species this spring.
There's a few others to be looking out for too.
I expect it to be a bumper crop this year.
The good news is, they're fairly easy to manage.
And they're fairly easy to manage
with some of the tools that we commonly utilize.
A wide range of products are effective and economical.
Glyphosate alone or in conjunction
with 2, 4-D are really effective.
And there's a lot of other products
that are effective as well.
Applications can be applied in the fall,
so if you did your applications this fall,
those are the most consistent, good for you.
But we can still get really good results in the spring.
We do have to be aware that as these weeds
get over six inches tall, some of the herbicide labels
will be in that six inches or less time frame,
so we wanna try and get 'em early versus later.
That's enough of my talk for my predictions.
You can come and see me in April and May
and tell me how wrong I am.
That winter annuals weren't a problem at all.
I'm gonna now shift gears and really focus
about how we can improve some of our
perennial weed management issues.
We can do this with burndown treatments.
There are effective options.
But there's challenges associated with these
in our northern climate.
Timing specific challenges and weed specific challenges.
Really these concepts overlap quite a bit,
so I'm gonna go through these and talk about these.
The first thing I wanted to do,
and this was kinda an interesting exercise,
I wanted to talk about what are the top 10 perennial weeds
that we see in our corn and soybean systems in Wisconsin?
What I did is looked at some of the past surveys done
over the last six or seven years
by Ross Recker and Nathaniel Fickett.
And classified those to come up with what are the top
weed species that we have in our Wisconsin system.
No surprise, common dandelions
was the most common perennial weed species that we had.
I had lots of quackgrass, yellow nutsedge.
White cockle or white campion was another one.
Canada thistle and field bindweed.
Those were the top eight.
Some of the surprising species
that you may not have thought of
is white clover was really common in many of our fields.
That's one that we may not consider a weed.
And volunteer alfalfa is one that we're seeing more
and more of showing up in our corn and soybean fields.
Finally, plantain species and horsetail were ones
that rounded up the top 10.
These are ones that we commonly see,
although there are a range of other species as well.
When we think about managing these species,
we have to think about, well,
when are they present in this system?
These species emerge and show up all at different timings
as we'll talk about more later.
I wanna emphasize that when they emerge
and when they are actively growing
is really critical to know in order to dictate
how we're gonna mange these species.
We have some species that are actively growing
early in the spring.
As I'll talk about, these are great ones to target
for increasing control
with some of our burndown treatments.
Like dandelion, quackgrass,
even clover and volunteer alfalfa.
These are ones that are growing really early in spring
and even late into the fall, and we can really effectively
target in our burndown treatments.
But, we have other species such as yellow nutsedge,
Canada thistle, our bindweed species and horsetail,
that don't grow actively during those burndown time frames,
in the fall
and more towards that spring time frame.
So those are ones that we really don't have as
good an opportunity to control in our burndown time frame.
We need to realize that a lot of these results
are gonna be very species specific.
Okay, so now we're gonna take a step back
and go back into Weed Science 101
looking at how herbicides work to maximize control
on some of these perennial species.
In order to maximize control of perennial weeds,
we need to get that herbicide absorbed into the plant,
and then we need to get that herbicide to move
or translocate into those perennial tissues.
That could be roots, rhizomes, tubers;
it just depends on the species we're talking about.
I'm gonna talk in a little bit more detail on each of these
with reference to burndown treatments.
How do we maximize absorption of herbicides
that we're applying in a burndown situation?
It depends.
Are these herbicides gonna be taken up
by the foliage or by the roots?
If these herbicides are gonna be taken up foliarly,
by the leaves, we want to treat when there's as many leaves
present to absorb that herbicide as possible, right?
That's a really important characteristic to remember.
Then the second thing we need to remember is
when you wanna treat when conditions are conducive
to allow for absorption of that herbicide.
What do I mean by that?
Well, those leaves aren't drought stressed.
The leaves aren't dead due to frost damage,
or something like that.
And most importantly, that temperature is warm enough
that absorption can occur.
Temperature's a really important factor
in herbicide absorption into those plants.
Usually temperatures above 50 degrees.
Now secondarily, if that herbicide is gonna be
taken up by the roots,
we need those roots to be actively absorbing that
nutrients, water, and those herbicide will be
moving up with them as well.
We'll briefly talk on this, but we have a little bit more
flexibility in temperature with that.
So what do you think?
What do you think how most of these herbicides
are absorbed when we're applying them
in a burndown situation, foliarly or by root uptake?
Silence.
Foliarly, right?
So that's really what I'm gonna focus on here.
But we do have herbicides
that can be absorbed by the root too,
and those are some opportunities to increase control
as we'll talk about.
How do we maximize translocation
of foliarly applied herbicides?
Well, we want to apply at the right timing
so that that herbicide can translocate
into that perennial tissue.
The timing is very phenology and species specific,
but really the two key timings I wanna
mention are the timing
when flower buds to early flowering is one good timing,
and then in the fall when green tissues are present
and right before those plants syness.
Those are the two key timings to maximize
translocation into the roots.
Now that can be some challenge with some of these
species to hit that flower bud to early flowering timing
so that fall timing might work a lot better
with some of our burndown treatments, as we'll see.
The key thing I want to emphasize though
is the worst timing to apply these for translocation
is early in the spring just after that plant emerges.
That's when it's really a challenge to get a lot
of that herbicide deep into that perennial tissue.
So spring or fall when we're applying a burndown treatments
which is our most effective time frame?
Experiments have been done in Wisconsin
and other states throughout the region,
and it's always clearly been shown,
even when we're making applications in the fall
in the middle of November
as you can see with this example here,
we're always getting significantly better control
with fall applications versus spring applications.
Whether they're herbicides that are only
gonna be absorbed through the foliage
versus herbicides that can be absorbed
through the foliage and the roots.
So if you can get these on in the fall,
that's by far gonna give you the best results
with the example with dandelion here.
And it can be quite dramatic in some years,
as you can see by this picture.
So now the question is, living in Wisconsin,
is how late in the fall can we go?
This was clearly a great year this past fall
to do some of these fall burndowns
so hopefully you were able to do that.
But how late in the fall can really vary depending on
what herbicide you use, what the weather's like,
and the status of the weed.
How resilient is that weed?
Can it grow late into the fall or not?
How stressed it is, how much leaf,
how much leaf area is present.
As a general recommendation,
to kind of sum up all of these
factors that I mentioned,
we recommend that you can make an application
when temperatures exceed 50 degrees Fahrenheit
for several hours the day of application
or within one to three days of that application.
So that's to counter many of these factors
I just talked about.
So when does that happen in Wisconsin?
Any guesses?
Pick a fall and it will be guaranteed
to be different every fall versus the other fall.
Here's some data to show you
that this 50 degree Fahrenheit time frame
is really a good reference.
This is some work we did on alfalfa suppression.
We did it with a very low rate of 2, 4-D, just one pint.
And we did it at two different locations
at four timings in the fall.
That blue bar was a late September timing.
That purple to reddish bar, I'm color blind
so if I'm gettin it wrong tell me,
is middle of October.
The lighter yellow bar is Halloween, October 31.
And then that light blue bar is middle of November.
What you see that there is some variation between
two of those locations, but that November time frame
is where that control really dropped off, right?
So let's look at the temperature and how that
temperature changed in that time frame.
This was done in 2008.
What we see with these arrows that are green
and that last one that's red are our
four different application times.
As you can see looking at the air temperature
that yellow bar is that 50 degree Fahrenheit time frame.
That September time frame, middle of October time frame,
well above 50 degrees Fahrenheit,
good absorption of those herbicides,
and as a result, effective control.
When we got to that Halloween day application,
we saw it was pretty cold.
That day of the application it didn't get above 50.
But we had some warm temperatures
that day after it was able to get above 50.
And we got some fairly decent control.
Little bit more variability, but decent control.
Look at that middle of November time frame.
That's really where the roof fell out
from underneath us.
And we were much lower than
that 50 degree Fahrenheit level.
So as a good rule of thumb,
if we can get to that 50 degree Fahrenheit level,
we can get good control.
This experiment really demonstrates that
at two different locations in Wisconsin.
Okay, so how late, in Wisconsin, how late
can we go and still expect to see
those temperatures above 50 degrees?
What I did is I took this information from our
Wisconsin state climatology office.
These are maps that show you the average 30 year
maximum temperatures over a 30 year time frame.
And what we see on the left there is October.
And what we see throughout most of the state
we can find in October days where temperatures
will get above 50 degrees.
Obviously, these are averages so there's gonna be
time frames when we're below there.
But if we look at all of those numbers,
we see they're all 50 degrees or above
on average in October.
So, likely well into October we can have success.
On the right side, we see November.
There what you don't see is any temperatures
above 50 degrees.
And so we're really rolling the dice
when we get into November.
I think October's a good time frame.
Probably you can go late into October
in southern Wisconsin and northern Wisconsin
you're gonna struggle to get past middle
of October in many years too.
But November is really when it's gonna be a challenge.
But it's a crap shoot.
We had many days in November
above 50 degrees this year too.
So it's highly variable from year to year.
All right, so let's say you wanna do a fall
burndown treatment, but you can't get those
temperatures above 50 degrees Fahrenheit.
What are some things that you can do?
One of the options that we found, is increasing the rates.
Make sure they're within label,
but increasing your herbicide rates
can offset some of those low temperatures.
We did some work with alfalfa again.
What we found, if we doubled the rate of 2,4-D,
we were working in Roundup Ready Alfalfa,
we could get similar levels of control
in controlling that alfalfa if we doubled the rate of 2,4-D
in temperatures less than 50 versus higher than 50.
So what we're doing is just adding more herbicide.
So even though a smaller percentage is absorbed,
we have more herbicide that gets into that root.
The other thing that we found with a lot of our
dandelion research has been shown
that some products can still
be root absorbed in those lower temperatures
even if we're getting poor foliar absorption.
Tank mixing some of these herbicides
like Autumn, Canopy, Express,
these do have the ability to be absorbed by the roots,
can offset some of those lower temperatures as well.
So that's another thing you can do.
Key thing though is we don't wanna make
those applications when the soil is frozen,
but just when those cooler temperatures exist.
The third option is what?
Wait til spring.
And that's often what we do because of other activities.
So if we are gonna go in
with some of these spring burndowns,
what are some things that we need to consider?
Number one item we need to think about is,
is those perennial weeds we're targeting emerged?
We not only need to have them emerged,
but we need to have considerable growth
so that they can actually
a, absorb that herbicide from
having a lot of leaves present,
and then two, hopefully that phenology's close
where it can actually translocate it
into the roots or perennial system.
We have a tool called the weedometer
that actually allows you to predict when emergence
of some of these species is gonna be
and when flowering is in Wisconsin.
You can just google weedometer
or you can go to the URL that I see there.
You can enter a lot of things.
You can actually shift the location,
so it can help improve the prediction.
If you're in northern versus southern Wisconsin.
Just for the sake of time,
I've showed you a screenshot
of some of the results with some of the
common perennial species.
What you see here are these green bars.
These green bars are the average
emergence time of these weed species
that I've highlighted there.
That's the range with the green dot being the average.
Then the yellow bars are the range of flowering
of these species with the yellow dot being the average.
This was taken from the weed garden at the
Arlington Ag Research Center.
Worked on there by Jerry Dahl in the late 1990s
and early 2000, that can create these.
But you can adjust the location
and it will come up with an estimate.
What you see here is many of our species
emerge in late March to early April
such as quackgrass, dandelion,
white campion and yellow rocket.
These are really good candidates for a late April
burndown treatment to be effective.
They're gonna be very well developed,
have lots of leaf tissue and be close to flowering.
But some of our species as you see
like Canada thistle, and more importantly,
field bindweed and nutsedge,
they're not even gonna emerge until after the first of May.
So we really shouldn't expect to get effective control
from our burndown treatments.
What are some other things besides emergence to consider
if you're doing a spring burndown treatment?
The other important thing is to think about
what those plant-back restrictions are
for the products that you wanna utilize.
Much of my talk is gonna focus on glyphosate and 2,4-D.
Why am I gonna focus on that?
Because in surveys that's what
the majority of people are utilizing,
and they have very minimal plant-back restrictions
present on the labels.
A lot of other products are effective and can be utilized
and have a lot of benefits such as residual control,
but we need to be really careful that we don't screw up
some of those plant-back restrictions on the label.
So what I thought I'd do now is show you one of our
demonstrations that we did to highlight
what happens long term with various spring
burndown treatments.
This is gonna highlight some things that you can vary
to help improve your control.
This is work we've done with Dan Heider,
with our IPM group here at UW on campus.
He applied either glyphosate, 2,4-D
or combinations of the two as burndown treatments
to some of his plots that were in continuous
corn or soybeans.
He applied them a little bit late, May 20,
so keep that in mind.
Then he planted these treatments two weeks after treatment.
So what we did is we went in and took a range
of measurements in these plots to look at
both the initial and then the long term benefits
of some of these different treatments
that I'm gonna show you.
What were the measurements?
Well, we came back 30 days after treatment
and looked at all the treatments,
and all the treatments had 100% dandelion control.
This is really important.
It's showing you just using a burndown treatment,
any of these, prevented that early season competition
with those crops which is our primary goal.
So they're all effective in that.
Now what we're gonna look at with our data is,
how can we improve some of that longer term control?
And we're really gonna make the assumption
that that longer term control means we're killing
some of those dandelions versus just suppressing
that early season growth.
How we collected that data was
we didn't look at the cover of those plants,
but we actually physically counted the number
of dandelions that emerged.
So if it was one dandelion
that really looked injured but it was emerged,
we counted it the same as a dandelion
that was robust and actively growing, had a bunch of leaves.
We came in in late July and evaluated this.
And what we saw is, on the y-axis here we have
the percent reduction in the number of dandelion plants.
So we're comparing it to an untreated control.
We can see if we applied glyphosate
at three-quarters of a pound,
Roundup at 22 fluid ounces
in our corn or soybean fields,
we were killing around 50% of those dandelions.
So we are getting some long term suppression,
but again we're probably only killing
about half of those populations.
The other half are probably the taller, older,
more mature plants that we're struggling to kill.
If we increase that rate from 22 fluid ounces
or three-quarters of a pound to a pound,
what happens?
Now all of a sudden our mortality jumps up,
almost doubles, gets around 85% in corn and soybeans.
So that's pretty good.
That's one simple trick that we can utilize,
just simply increasing our rate.
What happens if we add 2,4-D into the mix
with a low rate of glyphosate?
Well, again we get a similar response
that we do with increasing the rate of glyphosate.
We're getting an increase in control,
controlling anywhere between 80 to closer to 100%
of those dandelions.
Any guesses as to why we're seeing
better control in corn versus soybean?
Remember these are continuous corn
and continuous soybean plots.
Soybeans have a lot less residual cover.
We're probably getting much more robust populations
of dandelions in those continuous soybeans populations
just due to less competition for light.
That's my guess as to what we're seeing.
Then we had a 2,4-D alone treatment
and we're seeing that combination
of glyphosate and 2,4-D was also giving us
some better control than the 2,4-D alone.
We also did have treatments where you apply
glyphosate at three-quarters of a pound
and a pint of 2,4-D.
We saw in the corn plots we saw similar control
to the glyphosate at one pound.
But in those soybean fields we saw
a lot more variability in those results.
Think it's due to it's right at that tipping point
of effectiveness and adding that more 2,4-D
really did benefit it in the soybean systems.
Are other herbicides available besides glyphosate and 2,4-D?
These are the ones I'm talking about
and absolutely they're available
and they tend to be very effective.
But their effectiveness is specific to the weed species
and the time of application.
A lot of 'em have very specific restrictions in place
that just really prevent me to talk about them in detail.
Some like we've done research with like Autumn,
can be applied late into the fall
and are extremely effective.
Many of those that we utilize
that are cost effective like Autumn and Basis
are really effective but we still need to tank mix other
products like 2,4-D or glyphosate are recommended
to get that enhanced control.
The good news is some of these
other options are pretty effective
and they're generally very similar in cost.
But again, they have very specific restrictions.
Plant-back restrictions.
Some of 'em have very specific geographic restrictions
that limit their use in Wisconsin.
And some have weight restrictions.
So read those labels carefully.
To sum things up, what are some tricks
that we can do to increase our effectiveness
on perennials with burndown treatments?
Number one, scout those fields.
Know those weed species that are in your fields,
and know when they're emerging
and when they're sensitive to these applications.
Time those applications based on their growth.
I gave you some resources to help with that.
If you can, utilize fall applications when possible.
Hopefully, last fall you did a lot of that.
This is a really effective time frame to do that.
I know it's a struggle and it's a challenge.
We have lots of things going on in the fall.
If we have late harvest, it's hard to get it in every year.
So take advantages of those good falls
like we had that year.
If we can't make those applications
when temperatures are above 50,
try to use some products
that also can be absorbed by the roots.
We see some benefits that can occur from that.
If your gonna apply in the spring,
some options that you can do is first,
know those species that you're targeting in the spring.
Delay those applications as long as possible
until you reach that optimum timing,
so you can maximize that movement
of the herbicide into the perennial tissue.
Increasing that rate of glyphosate with dandelions
did show some benefit in increasing that,
so that's one option you can look at.
Adding additional growth regulator herbicides
like 2,4-D or even Dicamba,
if fitting in with the plant restriction
is another good option to utilize as well.
Realize that some of our species are really
not emerging during that time frame
like horsetail and bindweed,
and really need to be managed in crop
is probably your best solution.
That was that last bullet point that I said right there.
Hopefully, I haven't gone over too much time.
I would like to answer some questions,
but before I do I wanna mention that
another option is just planting perennial crops.
This is a great example of alfalfa
in a dandelion infestation and just having
a perennial crop on the landscape
can really do a lot of wonders for suppression as well.
Okay, if I have time for questions before lunch,
I'd love to answer 'em.
(audience applause)
Thank you.
(audience applause)