FARMERS are being told to hold their fire in terms of insecticide applications to control the newly discovered pest Russian Wheat Aphid (RWA).
RWA was discovered in South Australia in early winter and has since spread through parts of Victoria, as far east as Dingee, south of Echuca.
The news of the aphid’s presence has spooked growers who have been told of its ability to wipe out cereal crops in favourable conditions.
However, biosecurity officials across the nation are calling for calm, saying such scenarios are extremely unlikely.
Luise Sigel, grain pathology officer with Agriculture Victoria, told the audience at last week’s Birchip Cropping Group (BCG) expo not to apply a prophylactic insecticide, saying it was better to wait to confirm the pest was present in problem numbers first.
Entomologists say farmers putting out insecticides with the two active ingredients granted emergency permits for use to control RWA, pirimicarb and chlorpyrifos, risk killing off predatory species that will control the aphid along with the pest itself.
If too many of a predatory species are killed off, farmers risk seeing the insecticide application actually make the aphid problem worse.
“Aphids, whether they are an exotic species or not, are basically a sack full of food for predator species and will be controlled by them in the vast majority of cases,” said visiting US entomologist Jonathan Lundgren, speaking at last week’s Victorian No Till Farmers Association annual conference in Bendigo.
Dr Lundgren said the only time farmers needed to use insecticides was when an uneven spread of insect species populations emerged.
“That could be when you see a large build-up of problem species and few beneficials, so farmers should get out and have a look what is in their fields before making a decision on spraying.”
In Australia, species such as ladybirds, brown lacewings and hoverflies are all regarded as predators of aphids.
Dr Lundgren, who has courted controversy due to his criticisms of his former employee, the US Department of Agriculture, over its stance on pesticide use, said the problem of overuse of crop pesticides was not limited to control of aphids.
“For every species of insect pest we find 1700 beneficial species,” he said.
“We have largely eliminated biodiversity in our modern cropping systems and we now replace the function of the biodiversity with chemicals and the biotic resistances that used to be there are gone.”
Dr Lundgren said he questioned whether the insecticide applications were necessary, particularly if efforts were being made to boost beneficial species numbers through integrated pest management (IPM) techniques.
“It is easier to maintain simplified, in terms of biodiversity, agricultural eco-systems through the use of pesticides, but there are spin-off effects.”
He said insecticide use had a negative impact on pollinators, such as bees, which are critical for crops such as canola.
“I just don’t see that the return on investment is there.”
Dr Lundgren said his research had found that even when pest species were found, farmers needed to assess whether the insects were primary pests, those capable of major damage.
“In a field I looked at we found 107 pest species, which sounds bad, but then at a second look we found only 7 per cent of them were primary pests and none of them were found at economically damaging levels, so you need to look at the big picture.”
