GCTV Ep#9 Supplement – Glyphosate Resistant Weeds
Darryl Anderson: Presenter Next in our special report we look at a different
area of emerging resistance.
Jane Drinkwater takes up the story.
Jane Drinkwater: Narrator The problem of Glyphosate resistant summer
grasses is becoming one of the most pressing issues that growers currently face.
Australia currently has three species of summer grass confirmed as Glyphosate resistant - liverseed
grass, windmill grass and awnless barnyard grass.
Michael Widderick: Principal Research Scientist QDAFF Toowoomba
Recently there's been a survey conducted just on barnyard grass and it showed that out of
approximately 80 samples collected randomly across the region, sixty percent of those
were Glyphosate resistant.
Narrator: In the sample, which covered Dalby to Tamworth,
resistance was found from Goondiwindi to Narrabri.
Since the first case of barnyard grass resistance was discovered in 2007, there's been a steady
increase.
The thought of Glyphosate losing its effectiveness is a scary prospect for growers.
Michael Widderick: Once they have Glyphosate resistance they
can no longer use this product that they've relied on for many years, and Glyphosate's
such an effective product, it's cheap, it's safe and it's convenient.
Narrator: It’s so essential to weed control that there’s
a national body who’s focus is to prolong the herbicide’s working life.
Chris Preston: Chair Australian Glyphosate Sustainability Working Group
Glyphosate is our most important herbicide.
If you actually look at where it’s used around the farm it’s used in many many places.
If we lose Glyphosate for important weeds it’s going to greatly increase the cost
of weed management.
Narrator: It's the very usefulness of Glyphosate that
may be leading to its downfall because of its cost effectiveness and convenience, there's
a danger growers can rely on it too much, particularly for summer fallow control.
Michael Widderick: We've now reached a stage where Glyphosate
has been relied on for enough years that that pressure on the weed species has reached the
point where there's a lot of resistance out there.
The other reason I guess there's been an increase is we've moved away from conventional tillage
systems now to zero till systems, so we're placing a lot heavier reliance on our herbicides
in general.
Narrator: We're also seeing changes to how and when
weeds grow.
Michael Widderick: The emergence patterns of the summer grasses
have changed slightly over the last 10 or 15 years, and it's changed a lot for a lot
of our weed species.
For example, barnyard grass was once considered a summer weed species.
Now we're finding it emerge early in Spring, and later into Autumn as well so it presents
a whole new range of scenarios where we're trying to manage this weed.
Narrator: Michael's working on new strategies to manage
summer weeds, including those with Glyphosate resistance.
Michael Widderick: We're gaining more information on their emergence
patterns, on their seedbanks, and on even the speed of growth and seed production, so
we're finding out a lot more about the ecology of these weed species.
The other thing that we're doing is we're defining and developing tactics for the control
of these weed species and packaging them so farmers are able to apply them in combination
to achieve the best control they can and to reduce seed production on these weeds.
Narrator: One of the most useful tactics is double-knock.
Michael Widderick: We've seen that the double knock is extremely
effective on pre-tillering or early-tillering summer grasses, so this includes both windmill
grass and barnyard grass but also the troublesome weed Feathertop Rhodes Grass.
Narrator: Michael hopes to define when the most effective
time is to apply a double-knock and what interval works best between knocks.
Michael Widderick: Timing of the double-knock is critical.
A delay of even just one week can reduce your control dramatically.
If you do happen to delay your first or second knock, we have found that increasing the rate
of herbicide for both of the knocks does improve your control.
Narrator: And when Ground Cover reported on Windmill
grass last Summer, double-knock at the seedling stage was recommended as the most effective
control.
Chris Preston: Glyphosate does an okay job on seedlings,
but what we’ve been finding is that a double-knock strategy where you’ve got a Glyphosate mixture
first and you’re following that up with a bipyridyl will give you better control of
those seedlings.
Narrator: If you find Glyphosate isn't working as well
on your property as it has in the past, does this mean you have resistant weeds?
Michael Widderick: I guess when you consider herbicide resistance
it's pretty cut and dried, so a species that you once were able to control with a certain
herbicide such as Glyphosate, you now are not able to control that weed.
However there are other environmental constraints that will impact on the efficacy on your herbicides.
For example if you have a stressed weed, the herbicide isn't going to be as effective.
It's important that if you're finding that you have poor control of a weed with a herbicide,
you need to confirm that through testing and there are several testing facilities available
that can do that for you.
Narrator: And what action can you take if you find Glyphosate
resistance?
Michael Widderick: There are a number of different herbicide
options available, but with any weed species, the sooner you can get onto the problem, the
better, so if you have small, unstressed weeds, you're going to get improved control with
most herbicides.
Narrator: When Ground cover spoke with weed researcher
Jeff Werth in 2011 the advise he gave then on Glyphosate resistance in Barnyard grass
still supports the current thinking on rotating chemical use for all summer grasses.
Jeff Werth: Senior Research Scientist Weed Management QDAFF
If there’s an opportunity to use another herbicide group or even a residual herbicide
or something, do that.
So not concentrate on one thing, but just try and be more proactive rather than reactive.
Narrator: For Glyphosate effectiveness to continue,
growers need to adopt an integrated approach, finding problems early, and acting fast to
nip them in the bud.
Michael Widderick: Weed management in general relies on diligence.
This is especially the case when it comes to Glyphosate resistance.
It's important to identify problems as soon as they become a problem in your paddock,
so monitoring is critical.
If you don't currently have a Glyphosate resistance problem on your property, now is the time
to start using alternative tactics, so use different herbicide mode of actions.
Use non-chemical approaches as well, so prevention will ensure that you're able to use Glyphosate
into the future.
If you don't prevent, you will lose this herbicide.
ENDS
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