Northern and central New South Wales grain growers are being advised to continue monitoring crops for Russian wheat aphid (RWA) but only consider treatment if infestations are approaching potentially damaging levels.
NSW Department of Primary Industries (NSW DPI) research entomologist Zorica Duric said, figures from the Bureau of Meteorology showed 2019 was the warmest year on record followed by severe drought, while this autumn had been wetter than average for much of Victoria and New South Wales, which was likely to have slowed RWA population growth and spread.
Dr Duric, whose research is supported through Grains Research and Development Corporation (GRDC) investment, said RWA had been detected as far north as Tamworth, Currabubula, Breeza and Bundella on the Liverpool Plains last year and Condobolin and Coonabarabran in 2018, but there has been no sign of the aphid this season.
“We haven’t yet found any sign of RWA this winter, which is what we would expect given the conditions,” she said.
“This aphid does not like wet weather so if the forecasts are accurate and we get rain through spring, this may also suppress RWA.
“But even with predictions for a wet spring, growers and their advisers need to be monitoring crops, so any RWA present are detected and growers can make threshold-based decisions for effective management.”
Dr Duric recommends regularly checking barley, wheat, and durum crops for leaf streaking or leaf rolling, particularly in areas that appear visually stressed including along tree lines and heavily trafficked gateways.
“Growers need to make sure they don’t confuse these symptoms with other issues, such as manganese deficiency, herbicide damage and yellow dwarf virus. An effective way to check is to look inside the rolled leaves for the presence of aphids,” she said.
“If growers or advisers are concerned about identification, they can contact me directly or send me images or specimens for confirmation.”
Through research investments by the GRDC, a biological and ecological profile of RWA is being built to provide Australian grain growers with scientifically robust management tactics for the future.
These investments are being led by the research division of the South Australian Department of Primary Industries and Regions, the South Australian Research and Development Institute (SARDI) and delivered in partnership with cesar.
SARDI entomologist Maarten van Helden, who leads the GRDC-invested RWA thresholds-related research, said thresholds based on Australian conditions would be available soon and showed that so far, RWA had less impact than reported in overseas conditions.
“Based on the overseas findings, a spray application is recommended when more than 20 per cent of all seedlings are infested with aphids up to growth stage 32 (early stem elongation) and more than 10 per cent of tillers are infested with aphids from growth stage 32,” he said.
If infestation warrants chemical control, growers and advisers should refer to the Australian Pesticides and Veterinary Medicines Authority (APVMA) website for the most up-to-date list of products under registration or permit.
Good spray coverage and consideration of weather conditions (temperature, rainfall) in the 24 hours prior to and shortly after chemical application are important.
“If spraying is necessary, we do recommend growers use softer chemistry (e.g. pirimicarb) where possible to enhance the survival of natural predators and beneficial insects,” Dr Duric said.
The Tamworth-based researcher is also working on a project examining how RWA survive and reproduce on sorghum, the major summer cereal grown in the northern region. This project is part of the Grains Agronomy and Pathology Partnership (GAPP) between the GRDC and NSW DPI. Further RWA biology research is also underway to assess the host range of cultivated and wild grass species in northern NSW.
“This research aims to help determine how RWA interact with sorghum as well as identify which grass species play a key role in providing green bridge for RWA and could be controlled within paddocks, as part of a management strategy to minimise the impact of the aphid,” Dr Duric said.
Growers and advisers can also access a RWA resource portal which includes updates on current research, the latest RWA management advice and a distribution map, hosted by cesar.
RWA has recently been detected in WA, which is a timely reminder that the aphid is still expanding its range. Occurrences of RWA should be reported to the Exotic Plant Pest Hotline on 1800 084 881 which will assist improve understanding of RWA range and rate of spread.