Australian researchers have embarked on a mission to better understand the role of weeds and volunteer cereals, known as the green bridge, in promoting the survival and spread of the nation’s newest broadacre crop pest, Russian wheat aphid.
As part of new Grains Research and Development Corporation research, scientists are conducting active field research at more than 100 surveillance sites throughout Victoria, NSW, South Australia and Tasmania this summer to investigate how RWA survives between winter cropping seasons.
Elia Pirtle from research body Cesar said identifying RWA food sources and favoured weed hosts would be a particular focus of this summer’s green bridge surveillance.
This knowledge is considered 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.
First identified in South Australia in 2016, RWA is now present in many cropping regions across the country.
The two-year GRDC RWA research investment, led by the South Australian Research and Development Institute, 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.
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 recently, there was a lot of healthy-looking barley grass and the site was swarming with aphids,’’ Dr Pirtle said.
‘‘But it was also swarming with beneficials — there was more ladybug larvae than I’ve ever seen in one spot and they were really going to town on the aphids.’’
In the meantime, growers are being encouraged to perform their own RWA surveillance during the coming months.
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.