UNDERSTANDING what role weeds and volunteer cereals – known as the green bridge – play in the survival and spread of Russian wheat aphid is the focus of new research funded by the GRDC.
First identified in SA in 2016, RWA is now present in many cropping areas of this state, Vic, Tas and NSW.
This summer, more than 100 sites throughout the affected states have been set up for field research by scientists to investigate how RWA survives between winter cropping seasons.
This knowledge is pivotal in determining the risk of infestation and potential damage ahead of each new cropping season, as well as aiding RWA management planning and development of cultural controls.
The two-year project is also seeking to determine the regional production risk posed by RWA and the economic thresholds that will guide growers in effective management of RWA, taking into account growing regions, crop varieties and climatic conditions.
The collaborative project, called “Determining regional risks and economic thresholds for RWA in Australia”, is being led by SARDI, in partnership with sustainable agriculture research organisation cesar. The field trials also involve a number of farming systems groups.
cesar’s Elia Pirtle said identifying RWA food sources and favoured weed hosts would be a particular focus of the surveillance.
Dr Pirtle said samples were being taken from paddocks, fence lines and road sides, and relevant information being recorded included crops and grass species present, whether there were irrigated paddocks or waterways nearby, site topography, RWA growth stage, and the presence or absence of parasitoid wasps and beneficial insects in the sample.
“At an irrigated site we visited, there was a lot of healthy-looking barley grass and the site was swarming with aphids,” she said.
“But it was also swarming with beneficials. There was more lady bug larvae than I’ve ever seen in one spot and they were really going to town on the aphids.”
At cesar’s Melbourne research facility, a risk forecasting tool is also being developed to interpret the field data to help growers and their advisers plan RWA management strategies at the start of each season.
“We are creating interactive risk maps using real time data that predict the risk of RWA distribution and abundance into the next season,” cesar’s James Maino said.
“It’s a way of leveraging knowledge about the green bridge into useful tools that will help growers make crop protection decisions before, during, and after the season.
“You will be able to see broad differences between the states and can zoom in further to see what specific risk exists for a particular region, as well as see data generated by the project on absence and presence of RWA detected during our field work.”
In the meantime, growers are encouraged to perform their own RWA surveillance.
Weeds and volunteer cereals harbouring aphids may not necessarily show symptoms of infestation typically found in crops and populations are likely to be smaller at this time of the year, so Dr Pirtle advises growers to closely inspect grasses by unfurling leaves and checking inside partially emerged heads, paying particular attention to annual weedy barley grass.
Growers should also look for signs of predatory insect activity, such as mummified aphid bodies resulting from parasitic wasps laying eggs inside the aphid.
Local growers and advisers are encouraged to report occurrences of RWA to PestFacts at PIRSA.