GCTV Ep#9 Banding Fungicide
Narrator: In trials being conducted across the southern
and western grain regions new ways of using fungicides to control Rhizoctonia are being
developed.
It’s research that’s lead by the South Australian R&D Institute in collaboration
with these other research organisations and chemical companies.
And funded by GRDC and South Australia’s Grains Industry Trust Fund.
This trial site is located in the Murray Mallee.
Alan McKay: Principal Scientist SARDI This particular plot we have barley and the
three rows of this side have had the fungicide applied deep banded below the seed.
These three rows have not been treated with a fungicide and you can see in this area here
we have a patch of Rhizoctonia; it’s severely affecting the plant growth on this side.
The plants on this side are still affected but performing much better.
Narrator: The better performing rows in this plot had
a band of fungicide placed two to three centimeters below the seed.
In other plots fungicide was applied as a split treatment with half the dose placed
below the seeds, the other half on the surface.
Alan McKay: The fungicide at depth is banded through a
liquid fertiliser system and the fungicide at the surface has been sprayed on with a
fan-jet turned at right angles and it’s applied as a band about three centimeters
wide behind the press wheel.
Narrator: As part of the site selection process PreDicta
B, SARDI’s DNA based testing service, was used to confirm the presence of Rhizoctonia
and check for other pathogens.
Even before the seeds were sown the researchers had confirmation Rhizoctonia was a problem
here.
Many growers rely on their own observations for confirmation of the disease’s presence,
interpreting random bare patches as evidence of Rhizoctonia damage.
However the last decade has seen crops sown earlier due to dry growing seasons.
Bare patches are not often presence in these crops because they establish quickly while
the soil is warm.
During winter, when the soil is cold, root development slows and the fungus feeds on
the root system creating unevenness in the crop’s height.
Alan McKay: Yeah I’m sure that most growers and many
agronomists don’t necessarily link this uneven growth in sort of mid to late winter
as being due to Rhizoctonia.
People would normally be looking for these bare patches as a diagnosis or a way to identify
Rhizoctonia in the crop.
Narrator: While uneven height is far more common than
bare patches both symptoms can also be caused by other problems.
There’s only one way to unearth the truth.
Alan McKay: OK Paul we’ll collect one of the treated
plants out of this plot and we’ll go for a plant that looks like it’s not too badly
affected by rhizoctonia.
Narrator: It’s only by carefully uprooting the plant
and examining its root system that the presence of Rhizoctonia can be confidently confirmed.
Alan McKay: The system we use is to use a cut down shovel
put the blade between the rows and push straight down you don’t want to cut too close to
the plant because you’ll cut the roots off.
Push it down 10 to 15 centimeters then lift the plant out of the soil sideways.
If it’s a sandy soil you can gently shake the soil off but its better to actually soak
it off in a bucket of water.
Alan McKay: OK Paul you can see there’s a good root
system on these plants but it’s very hard to tell if there’s any Rhizoctonia on those
so lets wash those and see if we can see how healthy the system is.
Narrator: This sample is from a row where fungicide
was only banded below the seed.
Alan McKay: We can see on this plant all of these crown
roots up here, which we couldn’t see before with the sand, have been taken off with Rhizoctonia.
You can see the tipping quite clearly on these.
And the root system below the seed are in quite good condition and this is where the
fungicide was placed below the seed, about three centimeters below the seed, has protected
the primary root system.
Narrator: Crown roots are the last to develop and allow
a plant to tiller.
The fungus cuts back these crown roots stopping further tillering and so reducing the amount
of grain the plant can set.
These three samples show the impact of fungicide placement starting with an untreated plant.
Alan McKay: There’s no fungicide to protect either the
crown roots or seminal root system.
This plant has a seed treatment, which is the current practice for people trying to
use fungicides to protect plants from Rhizoctonia, so the seminal root system is not too bad
but we’re not getting any protection of the crown roots.
Here we’ve got fungicide banded above and below the seed at seeding and we’ve got
good protection of the seminal roots and we’ve also got good protection of the crown roots.
So it looks like we’re going to be able to generate some useful information that will
help support some banding recommendations for these new fungicides.
Narrator: Reduced tillering, uneven growth and bare
patches were evident across the trial plot.
Alan McKay: What people also haven’t appreciated until
recently is that rhizoctonia although it damages the seedlings and cause dramatic symptoms
in the crop, very early in the crop, most of the multiplication of rhizoctonia these
days is actually in the spring.
So by the time you get to harvest that’s when the fungus has reached its maximum levels
in the soil.
Narrator: Summer weed control research lead by CSIRO
has underpinned this improved understanding of Rhizoctonia build up.
The research has also demonstrated the importance of controlling summer weeds to reduce the
risk of Rhizoctonia.
Alan McKay: Its only been in the last couple of years
that we’ve really understood or appreciated that it’s the cereals and grasses that are
driving the rhizoctonia levels.
Narrator: Other research has also found that crop rotation
has a much bigger impact on Rhizoctonia levels then previously thought.
Alan McKay: Canola in particular is very good at reducing
the rhizoctonia inoculum down to a level that will cause minimal damage to a crop.
So the first wheat crop after canola is generally pretty good, doesn’t have a lot of rhizoctonia
damage in it, but by the time you’ve got to the end of that wheat crop, by harvest
the rhizoctonia levels will be back up to the pre-canola levels.
Narrator: While the Rhizoctonia project has a year to
go the results so far have been promising.
Alan McKay: And over the last two years we’ve averaged
about 6 percent yield increase with fungicides banded below the seed and in the split applications
the responses have been around 12 to 16 percent.
Narrator: And although the fungicides being trialed
are yet to be registered and application rates finalised, the work being done in these trials
will be used by the companies to include banding recommendations on their product labels.
In the meantime there’s a word of caution for those grain growers who believe they overcame
their Rhizoctonia problem years ago.
Alan McKay: I suspect that in many of paddocks that historically
had a problem and that growers consider they have now controlled it, if they have a closer
look at those paddocks they’ll find it’s actually still active in those paddocks.
ENDS
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