It was here at Tarlee in South Australia that Russian Wheat Aphid was first identified in
Australia in 2016.
Although the aphid might have been in the country much longer, no one knows.
Originating in the former Soviet state of Georgia the aphid first spread to South Africa
and North America about 40 years ago.
Since 2016 the aphids have been found through out Australia's southeastern states and are
moving north.
But the big question for the grains industry is will the Russian Wheat Aphid cause significant
yield loss, is it in fact a economic pest?
So that's one of the reasons why we do these trials, to establish thresholds to see one
aphid will not do damage, what about 100?
What about, I don't know how many aphids!
When do we expect that we will have yield loss in which case the pest has to be managed
by the farmer.
SARDI, the research division of Primary Industries and Regions South Australia with investment
from the Grains Research and Development Corporation, established trial sites and the project is
now in its second year.
So we've got trials going anywhere from Minnipa to Griffith down to Tasmania.
So we have a range of rainfall, we have a range of temperature and yeah we hope to get
good information about the regional risk of Russian Wheat Aphids.
At each site data on aphid movement and numbers is being collected.
So we have two trials that we're running.
The first one is where we're looking at whether the Russian Wheat Aphid is migrating into
the trial plots and we have treated seed with untreated seed of two varieties being Scepter
and Spartacus to determine whether or not they are causing economic damage.
Russian Wheat Aphids migrate into young crops in Autumn.
By spring they are ready to migrate again this time from the maturing crop to find younger
plants.
A pan trap is used to throughout the cropping cycle to capture winged forms of the Aphid.
One of these actually has wing buds as well.
In its next developmental stage it will actually take flight
After harvest the aphids over summering in volunteer cereals or other suitable grasses
and weeds.
Melbourne research facility cesar is investigating the green bridge aspect of the RWA thresholds
project.
While annual migrations of the Russian Wheat Aphid have been monitored by SARDI since the
aphid's presence was first identified.
In 2016 the field population was quite high however we didn't see the expected flight
migrations that we would expect to see however in 2017 we got quite high migrations but very
low field Aphid populations.
In 2018 we didn't see the migrations that we expected and so far this year we haven't
seen any migrations at all.
The second trial is focussed on Russian Wheat Aphid thresholds, and uses the same barley
& wheat plots as well as a durum wheat, and each commodity is treated three ways.
One of these treatments is a seed treatment; the second treatment is a Chlorpyrifos insecticide
spray at growth stage 40; and the third treatment is an untreated control and from this we hope
to determine thresholds, management options, as well the incidence of extreme pressure
and Russian Wheat Aphid damage.
You have to be aware that different varieties will probably have a different sensitivity
to Russian Wheat Aphids and even inside the wheats and inside the barleys we strongly
suspect that there are differences in susceptibility as they are differently adapted to different
growing conditions so there's still a lot unknown on varietal sensitivity to Russian
Wheat Aphids and we've done quite a few screenings in the green house looking at symptoms and
aphids but only on young plants and actually these trials are interesting because we will
bring them through to the harvest and we will look at not symptoms, symptoms is not damage,
what we need to know is their yield loss, that's damage.
Aphid counts are made every two weeks until Growth Stage 40, just before flowering, from
that point on Russian Wheat Aphids are unlikely to move into a crop.
To determine thresholds 25 tillers are selected at random from each plot, the aphids counted,
and the tillers left in those same plots.
So that we can actually state that the Russian Wheat Aphids have not been removed from the
plot and that the same population has always been present on the plot at the same date.
And then we take those numbers back to the lab where we put them onto the large data
set and then we actually start doing some population dynamic work looking at how the
aphid numbers have built up from last week or last fortnight as well as the symptomatic
expressions whether they have built up or stabilised or gone down.
In last year's untreated Loxton trial plots almost 30% of tillers had aphids.
In the USA aphids on 10% of tillers or greater is considered the threshold to trigger a spray
application.
The reason aphid numbers were allowed to build up in the Loxton plots was so yield-loss could
be recorded and according to Maarten van Helden the results were surprising.
So the plants in spite of this heavy aphid attack were still able to grow and produce
normally.
The only areas where we did have yield loss were areas where there was also drought stress.
The drought stress will stress the plants and that makes them more attractive to Russian
Wheat Aphids so they build up to higher numbers if you combine the two its probable that you
will have some yield loss.
Until the threshold research is finalised growers are urged to maintain the industry's
recommended Russian Wheat Aphid management strategy known as F-I-T-E.
Meantime the research has confirmed seed treatments will keep aphids off cereals during the first
6 weeks of growth but questions whether the cost to treat seed is warranted.
I think with the results we get from these trials we can now be quiet confident to say
in many situations there is no risk of Russian Wheat Aphids being building up to a damaging
population.
So it is a potential pest but to be a real pest it has to build up to high numbers and
the situation doesn't seem very favourable for Russian Wheat Aphids in the Australian
climatic conditions.