Australia - Check cereal crops for Russian wheat aphid

New South Wales grain growers are advised to monitor developing winter cereal crops for Russian wheat aphid (RWA) this season, and to consider treatment only if infestations are approaching potentially damaging levels.

The Grains Research and Development Corporation (GRDC) has released a new RWA factsheet incorporating critical, up-to-date information to assist growers and agronomists identify and manage the crop pest this season.

RWA was first detected in Australia in 2016 is now present in cropping areas of South Australia, Victoria, Tasmania, New South Wales and Western Australia. In eastern Australia it has been found in barley, wheat, durum wheat and barley grass and in 2019 was detected as far north as Tamworth, NSW, with experts warning it’s likely to continue to spread this winter.

NSW Department of Primary Industries (NSW DPI) entomologist Zorica Duric, whose work is supported by GRDC, said given the current environmental conditions it was probable that RWA would be detected in cereal crops further north.

“RWA survival is strongly regulated by environmental conditions. The pest prefers relatively warmer, drier conditions, where summer rainfall is 300–400 millimetres and temperatures do not exceed 37 degrees Celsius,” Dr Duric said.

“The pest was found on the Liverpool Plains and around Tamworth in 2018 and 2019, but in the hot, drought-affected year of 2019-20 there were no suitable host plants during summer, so unsurprisingly we didn’t find any RWA in our winter cereal samples.

“In 2020 we had a cold, wet autumn which was also not favourable for RWA. But so far this year conditions have been reasonably mild, so we are advising growers and advisers to start monitoring crops early for RWA.”

However Dr Duric said for definitive cost-benefit decision making for RWA growers should refer to the RWA threshold calculator which requires a single monitoring of crops at GS30.

Research shows while growers may choose to control earlier in the season cost-benefits could not be estimated as there was insufficient Australian information to determine intervention rules before G30, however overseas data suggested plants could outgrow early damage.

“RWA growth rates are influenced by plant growth stage, with younger plants supporting faster aphid reproduction than older plants,” Dr Duric said.

“Yield impact results from aphids migrating into crops at an early growth stage (during crop establishment) and building to high numbers leading up to head emergence.

“RWA often populates crop edges and stressed areas of the paddocks first, so checking these areas first is advised. Visible symptoms in wheat and barley can include long white, yellowish or sometimes purples stripes. Symptoms does not always mean RWA are present; unroll leaves to inspect and check the species.”

While Dr Duric said RWA was ‘definitely manageable’, early detection and assessment was important.

“Growers and advisers should use the RWA action threshold calculator that has been developed with GRDC investment to guide decision making,” she said.

“This calculator allows those on-farm to consider the thresholds for control, the presence of beneficial insects, crop growth stage and potential yield losses before deciding on the most effective action, if any.”

In summary, Dr Duric is encouraging NSW growers and advisers this season to follow a simple guide for RWA management. It involves:

• Find – look for aphids and the characteristic plant symptoms of infection including leaf streaking or leaf rolling on cereal crops and grasses.

• Identify – positively identify RWA by consulting with an industry specialist.

• Threshold approach – before deciding on your plan of attack consider thresholds for control, the presence of natural aphid enemies in the crop, crop growth stage and potential yield losses.

• Enact – take appropriate action: manage your next steps including encouraging beneficial insects and protecting honeybees before implementing control options.

GRDC has invested in significant research into RWA with research partners, the South Australian Research and Development Institute (the research division of Department of Primary Industries and Regions SA), Cesar Australia and NSW DPI. Information on current research efforts and the latest RWA management advice is available.