Virus damage mapped
GroundCover™ Issue: 113 | Author: Sharon Watt
The extent of beet western yellows virus (BWYV), which has decimated canola crops in parts of South Australia, Victoria and New South Wales, has been mapped after extensive testing of samples provided by growers.
The Victorian Department of Environment and Primary Industries (DEPI) laboratory tested thousands of plants resulting in a clear picture of where infection occurred.
By October, 2790 plants had been tested for BWYV and other viruses. Seventy per cent of samples tested were positive for BWYV.
In Western Australia, testing by the Department of Agriculture and Food, WA, virology group produced one positive sample.
A high incidence of BWYV associated with severe crop damage was confirmed earlier this season in canola crops in parts of SA and Victoria and unusually high infections were also found in several canola paddocks in NSW. This followed widespread infestations of green peach aphids (GPA) – the principal vector of BWYV – in canola crops during autumn and early winter 2014.
The GRDC recently announced an emergency funding package of $315,000 in response to the significant outbreak. This funding is being used in several areas, including forensic analysis of canola paddocks, communication to growers and advisers (assisted in SA with an additional $40,000 in emergency funding provided by the SA Grain Industry Trust), and preliminary assessment of virus levels in canola varieties to identify if there are any useful levels of resistance to BWYV for future sowing recommendations.
In the meantime, experts are encouraging growers to visually assess crops for virus symptoms and the presence of GPA, which transmit the virus.
Entomologist Dr Paul Umina, from cesar, says that while widespread frosts in August had slowed GPA activity, more recent warmer weather had hastened population build-up, particularly in moisture-stressed crops.
“We recommend that growers continue to monitor GPA populations closely. Check for the build-up of numbers and any significant numbers of winged aphids in a population, which signals that flights may be about to occur,” says Dr Umina, who is leading GRDC-funded research into insecticide resistance in GPA.
Dr Umina says it is important to distinguish between GPA and other winged forms of aphids before determining whether canola and pulse crops should be sprayed.
“It is pointless or even counterproductive spraying crops if there are local flights of other aphid species, such as winged turnip aphid,” Dr Umina says. To help with identification a pictorial guide is available via the cesar website (cesaraustralia.com/assets/Uploads/wingedaphids.pdf [4.1MB PDF]).
SA Research and Development Institute entomologist Bill Kimber says optimal timing for monitoring for aphids is late morning to early afternoon when temperatures are higher.
“GPA are most commonly found on the undersides of leaves, but also check stems, among buds and flowering heads,” Mr Kimber says. “We recommend visual monitoring, directly searching for aphids on plants. Check at least five points in the crop and inspect 20 plants at each point.”
Insecticides should only be applied if deemed necessary. Unwarranted spraying can increase the risk of insecticide resistance in GPA, as well as harming beneficial insects and honey bees.
Meanwhile, insecticide resistance among GPA populations continues to be mapped across the southern cropping region. Almost 40 populations have now been tested, with resistance to pyrethroids, organophosphates and carbamates found to be widespread.
Dr Paul Umina,
03 9349 4723;
08 8303 9536,
An industry-endorsed Resistance Management Strategy for GPA in Australian grains can be viewed and downloaded at: www.grdc.com.au/GreenPeachAphidResistanceStrategy
GRDC Project Code CES00001, DAN00179, DAW00229, DAS00139
Region South, West, North