CONTROLLING weeds will help minimise the infestation of Russian wheat aphid for the upcoming cropping season, according to experts speaking at a recent forum in the Mid North.
Growers and advisers from the region – one of the first to find the pest in Australia – heard from international and local scientists about what the future could be like with RWA.
This included a talk on the international experience from Colorado State University entomology professor Frank Peairs.
RWA has been in the United States, and Colorado, since 1986.
Professor Peairs said estimates showed the pest had cost the US state’s growers about $215 million in treatments and yield losses.
But he said the impact had subsided somewhat, with the last major outbreak in 2009.
“The first 15 years were the worst,” Prof Peairs said.
“It’s a sporadic problem, rather than our key wheat pest.”
Prof Peairs said there were several methods Colorado had used for managing the pest, including cultural controls, different plant varieties, biological control and chemicals.
There were 10 resistant wheat varieties available to Colorado growers, based on the presence of the DM4 gene.
“We are starting to see RWA able to overcome this resistance,” he said.
Cultural controls used in Colorado included diversified cropping, timing plantings to avoid peak times, and the push to control volunteer cereal crops or the green bridge.
Visiting French scientist Maarten van Helden, who has been working with SARDI to control the pest, agreed the green bridge was a key issue for the coming season, with conditions right for heavy growth.
He said RWA was most likely to live in barley grass and brome grass, and could not survive without a food source much longer than a week, if paddocks were sprayed before seeding.
In the past season, the wet winter, followed by spring rain, had minimised the impact of RWA.
Dr van Helden said the rain had washed aphids off plants, while some fungus varieties had attacked the aphids.
“Nature solved the problem, but I’m not sure we can always count on nature to do that for us,” he said.
“We have not seen any significant differences between the treated and untreated paddocks for yields.
“If we’d had a normal winter and spring, it may have been different.”
Biological control was another potential long-term solution.
Prof Peairs said, by the mid 1990s, effective natural enemies were a major part of controlling RWA.
“This was entirely due to native natural enemies adapting to the aphids, not the result of introducing new insects,” he said.
AgXtra plant pathologist Belinda Rawnsley conducted a series of trials in SA and Vic, looking at efficacy of different chemicals and spray applications.
The trials, which were conducted in September, found chlorpyrifos had more consistent successful results, but primicarb was “softer” on beneficial insects.
Prof Peairs agreed chlorpyrifos was the “gold standard”, but resistance was a key thing to consider.
Dr van Helden said RWA was present in most of the state’s eastern cropping areas, and, to a much lesser extent, on the Eyre Peninsula.
“You need to try and live with it,” he said.