To treat, or not to treat seed for Russian wheat aphid
Research entomologist Maarten van Helden from the South Australian Research and Development Institute (SARDI), a division of Primary Industries and Regions SA, visited the northern cropping region earlier this year and said it was inevitable Australia’s latest broadacre crop pest would soon be found in all NSW cropping regions and in Queensland.
RWA was first detected in Australia in 2016 and is now present in cropping areas of South Australia, Victoria, Tasmania and southern New South Wales.
“Last October, RWA was confirmed on the Liverpool Plains and at Coonamble in northern NSW and we believe it will continue to spread into the cereal growing regions of Queensland,” Dr van Helden said.
However, he said, monitoring in northern NSW and southern Queensland during 2019 (which was a combined effort of SARDI, NSW Department of Primary Industries and Queensland Department of Agriculture and Fisheries) did not detect any RWA presence on grasses or crops in the region during summer and autumn.
“While RWA is a high priority pest, it is manageable and the best thing growers and advisers can do is regularly monitor crops for signs of the pest,” Dr van Helden said.
“There are very distinct plant symptoms associated with RWA and early detection will give growers time to make informed, timely, cost-effective decisions about the appropriate management strategy for their situation.”
He said while neonicotinoid seed treatments provide effective early season control of RWA, prophylactic use of neonicotinoid seed treatments is discouraged and should be targeted at situations deemed to be of higher risk in areas and years where RWA pressure was high.
“Crops can be infested under warmer conditions in autumn, during the early stages of establishment, from wingless aphids walking off nearby senescing hosts, or winged aphids migrating from further away,” Dr van Helden said.
“Monitoring of early-sown crops for symptoms, including cereals sown as pasture, should occur for the first time four to eight weeks after sowing.
“Stressed areas of the paddock are often the first areas to be infested and hence monitoring may specifically target these areas.
“My advice for growers and advisers is to remain vigilant and monitor paddocks regularly, because we are positive this pest will arrive in northern NSW and Queensland and early detection will give growers time to determine the appropriate action for specific crops.”
Dr van Helden recommends growers and advisers follow the FITE (find, identify, threshold approach and enact) strategy which has been developed as a simple guide to RWA management. This 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.
“Growers are advised to adopt a threshold-based management strategy. Chemical control is warranted if infestations exceed thresholds of 20 per cent of seedlings infested up to the start of tillering and 10 per cent of tillers infested thereafter,” Dr van Helden said,
“Where aphid populations above these thresholds are eliminated before booting, yield loss can be prevented. Yield loss may be minimised through protection of the top three (major yield contributing) leaves.
“Current research investments by the Grains Research and Development Corporation will allow us to develop more regionally specific thresholds as our understanding of potential RWA impact on regional production improves.”
He said growers and advisers should consider the following measures:
- If infestation warrants chemical control growers and advisers should refer to the Australian Pesticides and Veterinary Medicines Authority (APVMA) website for the most recent products under registration or permit. Good spray coverage and consideration of weather conditions (temperature, rainfall) in the 24 hours prior and shortly after chemical application are important.
- If spraying is warranted, use softer chemistry (e.g. pirimicarb) where possible to encourage natural predators and beneficial insects, especially early in the season.
“Current GRDC investments will also increase our understanding of the role that summer hosts play in determining seasonal risk,” Dr van Helden said.
He also said it was critical suspected insect samples are sent to the Queensland DAF in Toowoomba or NSW DPI in Tamworth for formal identification. Growers and advisers in the Northern region are also encouraged to report occurrences of RWA to the Exotic Plant Pest Hotline on 1800 084 881. These reports will aid in improving understanding of RWA range and rate of spread.
For formal identification of RWA, Queensland growers and advisers can send samples to Dr Melina Miles, DAF, PO Box 2282, Toowoomba, Queensland. For details about sample collection contact Melina.Miles@daf.qld.gov.au.
In northern NSW, samples can be sent to entomologist Dr Zorica Duric, NSW DPI, Tamworth Agricultural Institute, 4 Marsden Park Road, Calala, New South Wales 2340. For details about sample collection contact Zorica.Duric@dpi.nsw.gov.au.