Elders keeping watch on Russian wheat aphid
Elders agronomists are keeping a keen eye on cereal crops for Russian wheat aphid (RWA) this season, following the first known outbreaks in South Australia’s mid north in 2016.
A common pest of grain crops around the world, RWA can cause losses of up to 50 per cent in wheat and 80 to 90 per cent in barley.
Following the discovery of RWA at Tarlee last year, it was soon found elsewhere in South Australia and across the border in Victoria and southern New South Wales.
While this season’s RWA outbreaks look to be more prevalent in drier regions like the northern Mallee so far, there’s no room for complacency, according to Elders Senior Agronomist, Brian Lynch.
“In the lead-up to this season, we advised our farmer clients to get on the front foot by treating their seed with imidacloprid and these crops are doing well to date,” Mr Lynch said.
“But every paddock I’ve seen that was sown with untreated seed is showing evidence of RWA at some level and that’s in a 100-kilometre radius of Loxton.”
Mr Lynch and his agronomy colleagues at Elders are working closely with entomologists from SARDI, researchers and plant health authorities to understand the pest and find effective strategies to manage it.
“I was fortunate enough to spend some time with one of the world’s authorities on RWA, Professor Frank Peairs from Colorado State University in the US, when he was in Australia in February,” Mr Lynch said.
Professor Peairs has spent decades investigating the biology and management of Russian wheat aphid.
“One of the key take-home messages from Frank’s work is that native spiders and other natural predators of aphids may take some years to adapt their life cycle and effectively use RWA as a food source,” Mr Lynch said.
“While these predators may be able to provide better control of RWA down the track, there’s a lot to learn about the pest under Australian conditions and our management strategies will need to evolve over coming years.
“For example, low rainfall areas like the Mallee which receive up to 250 mm of rain a year might be a sweet spot for RWA where crops are already stressed.
“The wettest September on record in the Mallee last year probably helped mask the damage from RWA, but what happens when we experience a typical Mallee finish?
“In the meantime, we are checking our clients’ crops for the typical symptoms of leaf streaking and rolling, so they can act quickly and apply pirimicarb. This is softer on beneficial insects than chlorpyrifos.”
Mr Lynch said RWA feed on grasses such as barley grass, ryegrass, volunteer cereals and irrigated crops over summer and may harbour in the Adelaide Hills.
“Geography certainly has a role to play, and so too does crop maturity at the time of infestation,” he said.
“For example, I’ve inspected crops from the same seed source, separated by as little as a few kilometres but on different soil types, and there are significant differences in the number of aphids present.
“Some summer species may be vulnerable and from what we’ve seen, the major losses have been in crops affected at early tillering.
“While we still have a lot to learn about RWA, we believe Elders’ best strategy this season is to monitor cereal crops region by region as we move into spring.”
Similar lessons in the south east
There’s a similar picture with Russian wheat aphid in the South Australian south east and western Wimmera, according to Elders senior agronomist based at Naracoorte, Jason McClure.
Cereals sown with imidacloprid-treated seed are doing well while RWA is prevalent in untreated crops.
“In one instance here, a farmer client sowed all of his paddocks with treated seed and no RWA could be found, but in another area where he was bulking up a new variety with untreated seed, it was easy to find RWA there,” Mr McClure said.
“In this region, growing conditions turned cold and wet during July, so RWA numbers slowed down, but the key question now is what happens in spring?
“While imidacloprid has managed any seedling infection so far, we will be monitoring our clients’ crops carefully in coming weeks and recommending treatment with pirimicarb or chlorpyrifos on a case by case basis if RWA reaches threshold levels.”