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 as a result of an intensive plant testing effort.
With the geographical spread of the virus now known, grain growers and their agronomists are being advised to cease submitting plant samples for testing.
The Victorian Department of Environment and Primary Industries (DEPI) testing laboratory has tested thousands of plants and results to date have provided a clear picture of where infection has occurred.
A map which outlines testing results can be viewed via the Grains Research and Development Corporation-supported eXtensionAUS agronomic resource hub atwww.extensionaus.com.au/spread-of-beet-western-yellows-virus/.
So far, 346 crop samples have been submitted to DEPI for virus testing and 2790 plants have been tested for BWYV and other viruses. Seventy per cent of samples tested were positive for BWYV.
Experts are now encouraging growers to visually assess crops for virus symptoms and the presence of green peach aphids (GPA) which transmit the virus.
Entomologist Dr Paul Umina, of cesar, says that while widespread frosts in August had slowed GPA activity, more recent warmer weather has hastened population build-up, particularly where crops are moisture-stressed.
“We recommend that growers continue to monitor GPA populations closely. Check for the build-up of numbers and the production of significant numbers of winged aphids in a population, which signals that flights may be about to occur,” said Dr Umina, who is leading GRDC-funded research into insecticide resistance in GPA.
Dr Umina said it was 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 counter-productive spraying crops if there are local flights of other aphid species, such as winged turnip aphid,” Dr Umina said.
To assist in the identification of winged GPA, a pictorial guide is available via the cesar website at http://cesaraustralia.com/assets/Uploads/wingedaphids.pdf.
SA Research and Development Institute (SARDI) 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 aggregating on the undersides of leaves, but also check stems, amongst buds, and flowering heads. Turnip aphid and cabbage aphid are the most common aphids to infest buds and flower heads,” Mr Kimber said.
“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. Aphid populations are often patchy and densities at crop margins may not be representative of the whole paddock.”
Insecticides should only be applied if deemed necessary. Unwarranted spraying can increase the risk of insecticide resistance in GPA, as well as impacting on beneficial insect populations and honeybees.
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. The latest resistance testing results can be viewed via http://cesaraustralia.com/latest-news/all/resistance-gpa.
An industry-endorsed Resistance Management Strategy for GPA in Australian grains has been launched and this can be viewed and downloaded viawww.grdc.com.au/GreenPeachAphidResistanceStrategy.
The GRDC recently announced an emergency funding package of $315,000 in response to the significant outbreak of BWYV in canola crops in the southern region. This funding will be used in a number of 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 different canola varieties to identify if there are any useful levels of resistance to BWYV for future sowing recommendations.
Through GRDC’s existing investments in virology, a number of other activities will be undertaken to assist in further understanding of this BWYV outbreak.
More information on BWYV and GPA is available via: GRDC Hot Topic website, www.grdc.com.au/BWYV and the eXtensionAUS website, www.extensionaus.com.au.
Paul Umina, cesar
03 9349 4723
Bill Kimber, SARDI
08 8303 9536
Frank Henry, DEPI Vic
Sharon Watt, Porter Novelli
Caption: Experts are encouraging growers to visually assess crops for virus symptoms and the presence of green peach aphids (pictured) which transmit the BWYV. Photo: A Weeks
GRDC Project Code
CES00001, DAN00179, DAW00229, DAS00139