Across the Southern grain growing
region, it's been common
to wait for opening rain,
spray for weeds, then
put in the crop.
But interim results from trials
at the University of Adelaide's rose
worthy campus are turning
that notion on its head.
One of the key messages for
weed management used to be to delay
sowing, so you have more time
for weeds to come up than you kill
them off and plant a crop,
which hopefully will be nice and
clean.
What we are showing through our
trial work is that these days
it works just in reverse.
When I was a student 20 years
ago, we were learning about daylight
saving, for managing raw grass
and getting that effective
knockdown out and
controlling, controlling the seed
bank, running it down.
So we had a clean crop.
Now, as Gurjeet mentioned before,
times have changed.
We've evolved another not just
herbicide resistance, but we've
changed the ecology of these weeds
and they're germinating
for a longer time throughout the
growing season.
And what we've seen here is that
what didn't work 20 years ago is
actually our best option in this
environment.
Associate Professor Dr. Gurjeet
Gill and agronomist Ben
Fleet are in the final
stages of trials at this South
Australian site.
It's part of a five year GDC
investment looking at weed
management across different
rainfall zones in South
Australia, Victoria and
Western Australia.
We are looking at
improving management of ryegrass
as well as brome grass and other
sites. Not here, obviously,
by using
what what we call cultural or
non-chemical tactics for weed
control in combination
with herbicides
to one,
minimize the impact of weeds
on our crop yields and
to is to enhance
the suppression of weeds.
So we minimizing their seed set.
The Roseworthy the campus
is in a mid-range rainfall
zone.
About an hour north of Adelaide.
We're looking at a very nasty
weed population with multiple
resistance and a huge seed
bank, which is going to set
a challenge for any grower.
In the wheat plots, they trialed
three seeding times in
May and June for
different pre emergent and post
emergent herbicide options
and three seeding rates
from a 100 seeds per square meter
to 300.
The canola crops were sown in
two lots, also
with four herbicide options
and a low and high
density seeding rate.
Here we go, Gurjeet.
This is a high density
with our effective
pre-emergent herbicides draw sown
just before the opening rains.
Yeah, yep, beautiful was the
21st of May.
As you can see, there's not a lot of
ryegrass in that at all.
And then we come down to
low seed density
with no effective frame just to
knock down a line.
And you can see how damaging that
raw grass can be when you let it get
bad enough.
A clear trend has emerged.
A triple threat to suppress
weeds.
Timely sowing early sown
crops into warm soils,
long days
highlight intensity is a
powerful tool in weed management,
so if you have the right break
to the season, make use
of that opportunity to get
a good crop competition and these
days with variable rate technology
and precision farming.
It, in fact, is possible for growers
to only be increasing seed rates in
the weedy patches or weedy areas.
Combine it with timely, early sown
crop.
But the third prong in all
this is still be using good,
effective herbicide options.
And as you can see Gurjeet, we've
gone from that early time of sowing.
And if we go down to a
late time of sowing, this is a month
later.
This is the one with a high end
herbicide control.
And the high seeding rate, but
there's still quite a bit of rye
grass.
You can see coming through.
So it just highlights that you need
all three parts of the package.
Yes, early sowing, good
seed rate and good herbicide option.
Knock it all together and you get a
good result.
And it's not just in the higher
rainfall zone.
The three pronged approach is
working.
Trials in the Mallee and Eyre
Peninsula shows similar results,
with the denser seeding rate.
So higher yield, better grain size
where we're getting more suppression
of weeds through going to those
200 seeds per square meter.
Even in those low rainfall
environments.
With rye grass in particular popping
up throughout the growing season
and becoming more resistant to
herbicide, the two researchers
had theorised that
earlier, denser seeding
would produce better results,
but even they have been surprised.
Well, particularly the sowing time
effect has really surprised us
in how dramatic it is.
When you double your density
from 100 to 200 plants per
square meter.
You can have the seeds set of rye
grass. We're still getting that
coming through consistently
now, but sowing time
responses have surprised us.
Majority of the sites in this
project, we've found that
the delayed seeding was a doubly
whammy of
increased weeds and lower yield.
So that's a pretty good lesson.
One of the big factors in all
of this is the change in
how long weed seeds
remain dormant
in the past.
Almost all your weeds popped
up at much the same time,
but that's no longer the case.
We are seeing a shift in weed
behavior because these tactics
of intensive cropping are selecting
for greater seed dormancy.
And what the what
we are doing through this cropping
system is killing off a lot of the
low dormancy parts of the weed
population and selecting
for the high dormancy.
We see weeds just keep coming
up for a month or six
weeks after the opening of the
season.
The same program also works
in open pollinated and hybrid
canola.
So we come down here Gurjeet.
So we've got with an OP canola
here in our first time of sowing.
We've got the lower
density on this side and a
higher density on this side.
So you can say it's probably
more dense in pods than say this.
What if we have a look
at the rye grass and we swing
through probably around here
somewhere and have a look and
you can see that it's pretty good
compared to the cereals, but.
Good herbicide option.
And then what about here in this
higher seed, right?
It's just the odd one there, but
they're pretty much shrouded out by
the canopy.
Yeah, it's quite impressive podding.
In the timely
sown canola.
They've found the vigour of
hybrid canola could also
pay dividends, particularly
if the crop goes in a bit late.
The difference is this is an open
pollinated type, canola
and that's a hybrid canola there,
so you can see the height
difference. But that's pretty
obvious, just the hybrid vigour, and
they're very similar specs, can all
of it? If we have a look into the
crop, then maybe
there are rye grasses seems to be
doing pretty well.
Yeah, yeah. I mean, how to get
enough light through that canopy?
Mm-Hmm. Mm-Hmm.
What about in the hybrid has that
look?
Yeah. So if we have a look in here
Still rye grass there and it's a lot
smaller.
But the size of ryegrass heads
or ryegrass plant is not even half
of what's in there.
All the data will be collated
after the crops are harvested,
but the researchers are confident
the mid trial results
are pretty clear.
It's no point being in one camp of
all herbicide or all cultural.
You need to take the best of
everything and combine it
to try to get your best of your weed
control.