The wheat aphid was first detected in south-eastern Australia in June last year, and managing it this year and beyond is the focus of several Grains Research and Development Corporation (GRDC) forums currently being held in South Australia, Victoria and southern New South Wales.
The forums are designed to equip growers and their advisers with the latest RWA research insights and practical management advice ahead of the 2017 cropping season.
One of the world’s leading RWA research authorities, Dr Frank Peairs from Colorado State University in the United States, will deliver key learnings from last year’s incursion, as well as ways to employ a tactical and considered approach to management.
RWA has caused US$850 million in damage since the 1980s, and Colorado was subject to an outbreak in 2003, sparking long-term research in the US.
Dr Peairs said while grain yield loss and insecticide treatments cost growers a total of US $215 million from 1986 to 2001 (and including 2009 when a spike in infestation occurred), damage caused by the pest has been relatively contained since then.
This was due to several reasons, the first being biological control: “Over the years, natural enemies have assumed a much more important role in regulating RWA abundance,” he said.
“Secondly, a number of modifications in cultural practices have been shown to influence RWA abundance. These include crop diversification, control of volunteer cereals and a variety of practices that promote crop health and vigour.
“The development of 10 RWA-resistant wheat cultivars has also assisted (although a new aphid biotype overcame the resistance in some varieties), as has the strategic and targeted use of insecticides, with chlorpyrifos being our most consistent treatment.
“But we must be very careful about dependence on a single chemistry – if the aphid is capable of responding to deployment of resistance cultivars, it has the potential to respond in a similar way to continual selection pressure with the same insecticide.”
Based on the Colorado experience, Dr Peairs said the relationship between wheat or barley yield and RWA infestation level is variable, influenced by variety, location and growth stage.
But he expected yield losses in Australia to be similar to those recorded in Colorado.
“Most studies indicate a reduction in wheat yield of approximately 0.5 per cent for every 1% infested tillers, from tillering through to flowering,” he said.
“Limited data indicates that yield loss in barley is likely to be substantially higher, perhaps 0.8% reduction per 1% infested tillers. This is without consideration of grain quality impacts resulting from RWA infestation.”
GRDC Southern Regional Manager Grower Services Craig Ruchs the forums allowed the research sector, growers and advisers to share their experiences of dealing with RWA for the first time last year.
One of those forums has been held at Riverton in South Australia’s Mid North, close to where RWA was first detected in Australia in May 2016.
“At Riverton, and elsewhere, there has been useful discussion regarding what was observed in-paddock last year and what the expectations are for the season ahead, especially if we experience a more normal rainfall pattern over winter and spring,” Ruchs said.
Dr Peairs and other leading pest management experts have encouraged growers to act now and take a pro-active approach to RWA management in 2017 by eliminating the “green bridge” of grass weeds and volunteer cereals that is providing ideal over-summering conditions (food and habitat) for RWA populations.