Hello and welcome to the Sports Turf Scoop.
My name is Tom Serensits and I manage the
Center for Sports Surface Research at Penn State.
Today we will be talking about plant growth regulators
and how they can help your field.
However, before we get into how a plant growth regulator can help your field,
let’s talk a little bit about what a plant growth regulator is
and how it works.
So a plant growth regulator, or a PGR
as you will often hear them referred to as,
is a compound that regulates plant growth
and it works by affecting plant hormone levels.
So just as in humans, if we start playing around with
different hormone levels in the body
we can affect growth and development.
The same thing happens in plants –
when we apply a plant growth regulator,
we can affect growth and development
and either increase growth or stunt growth.
Now when we think about a plant growth regulator in turf,
we typically think about something that slows the growth
of the plant down, and in most cases that is correct in turf.
However, by definition, a plant growth regulator
can either increase or decrease growth rate.
So, for example in certain horticultural applications,
PGRs are used to increase growth rate,
but again in turf we typically use them to slow the growth rate
of the turf down and we can see that in the picture here
– this bermudagrass plant –
the small plant has obviously been treated with a PGR,
in essence creating a miniature plant.
When we talk about the PGRs that we use in turf,
one of the most common contains the active ingredient trinexapac-ethyl.
This is the active ingredient in Primo Maxx
and other post-patent PGRs that contain trinexapac-ethyl.
The way trinexapac-ethyl works is that it inhibits gibberellic acid
and gibberellic acid is a plant hormone.
So gibberellic acid is responsible for cell elongation.
So if we are inhibiting this plant hormone, or inhibiting cells elongating
and in essence creating smaller cells inside the plant,
this translates into a reduced growth rate.
Now obviously a reduced growth rate is the number one target
when we are applying a PGR in most cases,
however there are some side effects,
namely increased rooting and increased tiller density.
Now we are starting to see some things
that may help us on sports fields.
So if we could take a look inside an individual turf plant,
this is what we would see.
The top picture here is what a cell would look like
when there are normal levels of gibberellic acid.
The bottom picture show what cells would look like
after a product with trinexapac ethyl has been applied.
So we can see the cells are much smaller and shrunken down.
That translates into a slower growth rate.
So how is a product like this going to help us on a sports field?
Well, if we think about it quickly –
why do we want to put something on our turf
that is going to make it grow more slowly?
If we are trying to recover from damage we want to increase growth,
and certainly that is a concern on a heavily used field.
And, of course, the main target when we apply PGRs
in most cases is a reduced shoot growth rate.
However, it is those side effects that we need to look at
in terms of a sports field perspective.
If we can increase tiller density
in essence what we are doing
is increasing the number of plants in an area.
Also if we can increase rooting –
now we are creating a stronger field
that is better able to tolerate the stresses of play
and provide a better playing surface for the athletes.
So when we talk about a better surface for athletes,
what are we really talking about?
I think what we are talking about is a more stable surface.
When we have low surface stability,
we tend to have excessive divoting.
We can think about divoting as the complete shearing
or removal of the turf root system from the rootzone.
Certainly any field can be prone to excessive divoting,
and really a number of factors can make a field prone to divoting
and one of those factors is the soil type.
So looking at professional or collegiate stadiums
we tend to make the rootzones of these fields
out of a high percentage of sand.
We do that for two reasons –
one to increase drainage
and two to minimize the effects of compaction.
However a trade off with that is
we lose the cohesion between soil particles.
Now, we are relying heavily on the plants
and the root system of the plants
to provide the surface stability and divot resistance.
The same thing can and does occur on native soils fields as well
however we tend to see divoting
as an even bigger problem on these high-sand fields.
But, in any case, what we are trying to do
with a plant growth regulator application is improve plant growth,
again increase tiller density, increase rooting
and that hopefully will transfer into increased surface stability
and higher divot resistance.
So that was the idea behind a research study
we conducted here at Penn State.
We wanted to see if the application of a PGR
can increase surface stability
and more specifically increase divot resistance.
We looked at can Primo increase divot resistance of Kentucky bluegrass.
We had several different Primo application schedules.
We applied Primo at a half ounce per 1000 square feet
according to the label.
We applied Primo from May through July –
in essence this was a pre-conditioning treatment –
we were trying to simulate a field situation
where we have no activity during the spring and summer
and then we have a fall football season.
So here we are applying Primo –
three applications from May through July
and we are stopping those applications once the season starts.
We found that on a sand-based rootzone,
we found a 10 to 20% reduction in divot size
when we used this pre-conditioning Primo treatment.
We did our testing, we took divots,
we reduced divot size indicating that we improved divot resistance
10 to 20% when we pre-conditioned the turf with Primo.
When we did the same study on a native soil field,
we still saw a 10% reduction in divot size
so again translating into increased divot resistance
and more surface stability with the application of Primo
from May through July.
Now we also in another treatment
applied Primo from May through October.
So, we had those three applications May – July
and we continued those applications all of the way through October.
Now while this did not hurt us in terms of divot resistance,
it also did not improve the divot resistance
like we saw in that pre-conditioning treatment.
The best thing that we found in terms of this study was to pre-condition,
or get the field ready for the stresses of a football season
by applying Primo and then stopping those applications
once the season started.
Why did we see those improvements?
Well, for that, we can look at the tiller density
and root mass measurements that we made.
We found that the Primo treatments from May through July
increased tiller density by up to 15%.
In terms of root mass, that May through July treatment
increased root mass by 10%.
So now we have the combination of increased tiller density
and increased root mass –
now we are starting to see why we produced
a more divot resistant turf with those applications of Primo.
So the overall conclusion from our research was that
when Primo was applied in the spring and summer,
we saw an improvement in divot resistance for fields used in the fall.
Now it is important to note that this is for fall-only field use.
If you have year-round use of a field,
this may not be what you want to do.
So our project we had a field that was not used in the spring
and summer but was used in the fall.
Again the reason behind that increase in divot resistance
was an increase in tiller number and an increase in root mass.
If we are going to use a PGR
with the active ingredient trinexapac-ethyl on our field,
there are a few things you must think about.
First of all, this is a foliar-absorbed PGR,
meaning that it must dry on the leaf.
According to the label, that must be
a minimum of one hour on the leaf
in order to make sure that that penetrates down into the plant.
You can expect a 50% growth reduction.
The effects usually occur three to five days
after that initial application.
Now when we are looking at application rates,
we want to make sure we are reading the label
and making sure we are following the right time schedule.
In our study, we went out at 0.5 ounces per 1000 square feet
on 28-day intervals.
You certainly can cut that rate in half and go out at 14-day intervals
just making sure that you are matching up you rate
with your interval timing.
One thing to note is that you may have some discoloration
after the first application of the year,
but then in general we start to see a darker green plant
as a result of that trinexapac-ethyl application
again because those cells are smaller,
they are more tightly packed
we have the same amount of chlorophyll in there –
that creates a darker green plant.
So, just an added benefit to trinexapac-ethyl use.
Now of course there are also situations where
we don’t want to apply a plant growth regulator.
We just talked about earlier that if we have year-round use
that may be something we don’t want to do
in order to make sure that we can recover
from damage that is occurring month after month.
Another thing that we don’t want to do
is apply a PGR to stressed turf.
For example here in this picture
we see severely drought-stricken turf.
We don’t want to go out there with a PGR application
or really any pesticide application for that matter
because the turf is in a stressed condition.
You want to make sure that we are not applying a PGR
when the turf is already stressed,
whether it be from drought
or anything else that may cause stress on a field.
Another situation that may not be the best time for a PGR application
is immediately before or after cultural practices
such as core aerification or vertical mowing –
this will delay the recovery process.
So, if this is something that you are going to do,
it is best to wait until that turf recovers
from those cultural practices
and then get on a PGR treatment regime.
Another thing that you need to think about
when your turf comes out of that trinexapac-ethyl growth inhibition –
there is going to be a growth surge or rebound effect
and this is documented in the research
where we talk about a minimum of 160% growth rate
in the days following that turf getting out of that growth inhibition.
Now this is something you can use to your advantage as well.
We talked about timing that last application
so it stops before the football season starts.
We can time that perhaps to come out of that growth regulation
after the first weekend of games –
now you are going to get a flush of growth,
now you are going to see some increased recovery
early in the season because you are getting that rebound effect
that we commonly see with a trinexapac-ethyl application.
Where else can a plant growth regulator
fit into your sports turf management?
Well, we can put trinexapac-ethyl in paint.
Specifically, the label for Primo Maxx says
1 ounce of Primo per gallon of paint.
This is a great idea if you are painting logos,
especially off the field and anywhere that is not going to be
heavily used and the paint is going to get worn off by players.
So again, if you have lines on a field that is not heavily used or any logos or
anything that you want to make that paint last for a longer period of time
and not mow it off, a little bit of plant growth regulator
in that paint will help make that paint last for a longer period of time.
At the same time we want to make sure
we are not adding a plant growth regulator like Primo
to our paint where it is not going to really be a benefit.
Here’s a perfect situation – a heavily used field –
it is not the best idea to put Primo in that paint
where we are going to paint lines on a field
where that paint is just going to get worn away just by general play.
So we want to be careful and keep that plant growth regulator paint
more to the outside that is not going to be worn away
very quickly on an intensely used field.
So again, endzone logos or out of the way areas -
a great way to help you paint last longer.
It is not going to really be much of an advantage
in a situation like this down the middle of a field.
Some other instances where a plant growth regulator
would be a good idea on a sports field
is during non-sporting events when the field
is going to be covered for an extended period of time.
So things like concerts or graduations –
we want to make sure that we minimize the amount of stress
on that turf during the time that it is covered.
The best way to do that is to slow the growth rate
of that plant down with the use of a PGR.
Some recommendations for preparing the turf for a non-sporting event
when the field is going to be covered are given by Steve LeGros.
Steve is involved a lot in professional stadiums
when these large concerts come to professional stadiums.
He is often brought in by the turf manager
to help them keep the turf as healthy as possible
during the time that field is covered.
What Steve recommends is that Primo applications
start at least two months before the event,
making sure that we are keeping up with our application intervals,
whether we are looking at 14 day
or 28 day intervals in the case of Primo.
We want a Primo application 21 days before the field is to be covered –
that builds in a little bit of safety with that 28 day interval –
making sure that if there is a case when that field
is unexpectedly covered for a few extra days,
we are still going to not get to that growth surge stage.
Finally, we are going to use that growth surge
to help us grow out of damage.
So imagine we are peeling off whatever floor covering is used,
n a few more days we are going to get a growth surge
when that turf comes out of that growth inhibition from the Primo –
now we are going to start to accelerate that recovery process.
What about Poa annua control?
Certainly depending on your part of the country
Poa annua may be a big issue on your field.
You may have heard that plant growth regulators
can be used to help control Poa annua
but we want to make sure that we are using the proper plant growth regulator
if this is something that we want to look at doing.
This is a case that we are not going to want to use
a product with the active ingredient trinexapac-ethyl
like a Primo Maxx.
We are going to want to use a product
that contains the active ingredient paclobutrazol,
which is the active ingredient in Trimmit.
So it is a little bit different –
we talked about trinexapac-ethyl being foliar absorbed,
now we are talking about a PGR
that is root absorbed so this must be watered in.
We talk about this in terms of Poa annua suppression,
this isn’t really Poa annua control because it takes a long time
and it is not necessarily a pretty process
as we get this Poa out of our field
because there is some discoloration
and you can mask this discoloration
with a little bit of nitrogen added to that paclobutrazol
when you go out and spray it.
It is a little bit more of an aggressive PGR –
it will slow the growth rate down
for a little bit longer period of time
than we talked about with trinexapac-ethyl –
so generally about 6 to 8 weeks of slow growth.
But, again, over time we can start reducing the Poa annua population;
however this isn’t a magic bullet,
you are not going to be able to go out with a few applications
and remove all of your Poa –
it is part of a process, and a multiyear process,
to slowly widdle down your Poa annua population on your field.
So if this is something that you are interested in doing,
we want to make sure we know what to expect –
we want to be careful,
we want to know how much Poa we have to begin with.
A lot of times you will say –
well I have 15 or 20% Poa –
maybe it is 30-40% –
do you really want to make 30-40% of your field weak
with these paclobutrazol applications?
It certainly depends upon the time of the year
that we are going to do that.
Can the discoloration be tolerated? Is this a high-profile field?
Do we need to worry about the yellowing of the Poa annua? –
something else to think about.
Can you establish turf in its place?
We want to make sure that we get our desirable turf species
in there to take the place of that Poa
because we know that Poa annua produces a large number of seeds.
So, certainly the seedbank is there in the soil.
We want to make sure that we can beat
that seedbank to the punch
and in most cases have some perennial ryegrass there
to take the place of those dying Poa annua plants.
Also something to think about is during play, during a season,
actively growing Poa is really better than injured Poa –
that is going to be an even weaker plant.
We want Poa out of there because it is weak,
it tears up easily, it is not a good surface.
If we go in and injure that during play
we are going to have an even weaker surface.
Again, be ready to seed your desirable species –
in most cases that is going to be coming in with perennial ryegrass,
get a quick germination –
a quick cover to help crowd out that Poa
and keep it from returning as best we can.
What is the timing that we want to do this?
For football fields, we want to do it in the off season
so that means starting these applications in the spring.
Baseball fields – it is the opposite,
we want to do these applications in the fall.
We want to make sure we are not applying in hot weather.
Again, any time a turf is stressed and we apply a PGR,
that is just going to make that stress that much worse.
Another thing to think about, is on the label –
if you are doing a widespread application –
you can’t seed 6 weeks prior to
or 2 weeks after the application of paclobutrazol.
We just talked about making sure that we have ryegrass seed there,
but we really need to wait for these windows
or we are going to start to see the PGR start to affect that seed.
So it is not an easy process –
there are a lot of things that go into it.
Again, it takes time to get the Poa out,
but it is just something to think about if you have a Poa annua problem,
you can get on this paclobutrazol program
and over time start to reduce your Poa annua population
and build up your desirable turf.
So at first glance you may wonder
why would I use a plant growth regulator on a sports field? –
I need as much growth as I can get to recover from damage.
And, certainly that is the case in some situations.
However, we showed that in certain circumstances
a PGR can be beneficial to you as a sports turf manager.
The first thing we talked about was pre-conditioning the turf
prior to the season to increase divot resistance
and increase surface stability.
We talked about other uses –
putting Primo or any other PGR in paint
to help those paint lines last longer.
Non-sporting events –
helping the turf deal with the stresses
of being covered for a long period of time,
even Poa annua suppression with paclobutrazol.
So certainly don’t discount PGRs
just because you don’t want your turf growing slowly
on your sports field.
There are ways and there are techniques
to use where a PGR can be beneficial
and make your sports turf that much better.
So I ask you to give PGRs a second look.
See if they fit into your management program.
For any information related to PGR research
or anything else that we do here at Penn State,
please visit our web site at ssrc.psu.edu,
you can “like” us on Facebook
and you can also follow us on Twitter @PSUsportsturf.