SARDI Cereal Aphid Risk Assessment SA project data collected last week has revealed Russian wheat aphid infestations have decreased in all three trial plots at Loxton, Bool Lagoon and Roseworthy.
Barley, wheat and durum wheat varieties were sown from April to July this year and monitored fortnightly for RWA populations and damage.
SARDI entomologist Maarten van Helden said trial sites that had seed treatments applied showed it had been effective at controlling RWA populations and protected against early infestation.
He said aphid migration had not been observed after June and recent widespread rainfall had also affected RWA numbers.
“Last week’s observations showed the number of tillers carrying aphids declined – so that is an indication that the aphids are being washed off,” he said.
“It is unanimous the rainfall had a good effect but it will be another few weeks before we can see if RWA populations were heavily affected.
“We are still finding high numbers in the tightly-rolled leaves where the aphids are hiding.”
Observations highlighted that early-sown cereals had been more affected by RWA infestations.
“Each month about 300 tillers were observed – we found curled leaves and streaking of the leaves, particularly in the earlier sown crops,” Mr van Helden said.
“If the aphids build up in spring, we expect to see a reduction of tillers that have heads with seeds in them.
“Last year in separate observations, yield reduction did not occur because we believe the RWAs were simply washed off.”
At the GRDC update in Spalding last week, SARDI entomologist Greg Baker said winter was a holding time for the pest.
"RWA populations crashed in September because of the high rainfall,” he said.
"Our trials showed no yield difference in sprayed versus unsprayed crops last year, because of the effect of high rainfall."
Insecticide treatments will not be applied to trial sites and crops will be harvested to record damage.
Positive trial results observed
THE Loxton Russian wheat aphid trial site recorded a 25 per cent drop in pest numbers last week, with some crops also producing new and uninfested tillers.
SARDI entomologist Maarten van Helden said RWA populations at Roseworthy were stable after an earlier decline in recent weeks, but not a single RWA was found at Bool Lagoon trial plots in last week’s observations.
“Although the explanation is not clear, the situation at Bool Lagoon and Roseworthy seems to confirm the positive effect of rain,” he said.
Mr van Helden said about 50 parasitised aphids, called ‘mummies’, were collected from the Loxton trial site.
“This is a good sign because mummies are from wasps that lay their eggs inside the RWA, then the aphid is slowly eaten,” he said.
