Green peach aphid and beet western yellows virus in canola
17 July 2014
By Dr Paul Umina, cesar, and Frank Henry and Dr Mohammad Aftab, DEPI Horsham.
Early spread of the green peach aphid (GPA) (Myzus persicae) has severely damaged early sown South Australian canola crops and transmitted beet western yellows virus (BWYV). In Victoria and NSW, high GPA numbers have been reported with BWYV detected in many crops, although crop damage is not as severe as in SA. Crop samples from NSW, SA and Victoria have been sent to DEPI Victoria for testing: see the mapped results
SARDI and DEPI are no longer able to accept samples for testing. Growers are advised to visually assess crops for virus symptoms and aphids. Crops that are already infected do not require spraying. However, if aphids are present it may be beneficial to spray parts of crops not already showing virus symptoms or paddocks without symptoms if there are aphid infestations and BWYV is known to be in the area.
Advice – PestFacts south-eastern Issue No. 6
Experts agree that spraying to control GPA while winter conditions persist is probably not warranted in most areas.
Aphid numbers are decreasing due to the colder weather and they are less mobile reducing the risk of further spread of the virus. However, growers should remain vigilant, monitor for colonising (winged) aphids, and be prepared to apply insecticides in late winter or early spring to limit virus spread into canola and pulse crops. Although unlikely in most regions, if aphids are actively flying at present, chemical control should be considered.
It is important to only use insecticides registered for the crop and situation, and to comply with the label directions. In cases where sprays are needed, the use of ‘softer’ insecticides such as pirimicarb should be considered. Fortunately, many GPA populations in NSW and Victoria (unlike in many other states where resistance is widespread) can still be successfully controlled with pirimicarb. If growers experience control failures involving pirimicarb do not reapply the same chemical. Please note, pirimicarb is more effective if applied when temperatures are above 20°C. Transform® is also registered in canola and field reports suggest very good control of GPA. Paraffinic spray oils can also be used for suppression of GPA.
Monitor aphid populations (and their flights) over the coming weeks using a combination of yellow sticky traps and directly searching for aphids on plants. GPA are typically (but not always) found on the undersides of leaves. On rare occasions in canola, GPA can be found on the flowering spikes in spring; often in mixed populations with cabbage aphids and/or turnip aphids.
Symptoms of BWYV in canola
The symptoms of BWYV in canola, which may not be evident for 2-5 weeks after infection, include yellowing and purpling of leaves starting from the lower leaves, inward cupping and stiffening of leaves, mottling, stunting and premature bolting.
In addition to the virus, it is likely that GPA caused significant damage to many crops as a result of their direct feeding on plants. This virus infects phloem (conductive tissue) resulting in symptoms that resemble nutrient deficiencies, herbicide damage, physiological stress or other disorders.
Canola is most susceptible to BWYV at the rosette stage, when infection can lead to high yield losses. Generally, the yield consequences of BWYV decrease with infection at later stages of crop development. However, canola crops remain susceptible to yield losses from BWYV infection until approximately the mid-podding stage.
Pirimicarb and Sulfoxaflor are currently registered for aphid control in canola crops in this state. Check with your local Department of Agriculture or the Australian Pesticides and Veterinary Medicines Authority (APVMA) for any off-label permits each growing season.
While bees are valuable for pollinating crops they are highly vulnerable to pesticide applications within their forage zone. cesar Pestfacts (13 Aug 2014) has provided a detailed guide to understanding the risks and what you can do to prevent damage to bees. You need to login to view this content.
Green peach aphids and resistance
Recent resistance mapping research lead by cesar has found that GPA populations across Australia have resistance to multiple insecticide groups. High levels of resistance to carbamates (e.g. pirimicarb) and pyrethroids are now widespread across Australia. Moderate levels of resistance to organophosphates have been observed in many populations.
Stay up to date with the latest information via field crop diseases newsletters and social media
Get more information on Diagnosing beet western yellow virus in canola from DAFWA.
DAFWA Aphid management in canola crops has information on aphid identification, predators and management.
Feature article on the recent outbreak in PestFacts south-eastern Issue No. 6, 10th July 2014 Green peach aphids and beet western yellows virus (registration required)
Feature article on the recent outbreak in Crop Watch Vol 11 No 4, July 2014 Green peach aphids and beet western yellows virus (623kb PDF)
GRDC Radio Interview with Dr Paul Umina 16/7/2014 on green peach aphid behaviour and management. Interview commences at 4:24.
GRDC Resistance management for green peach aphids factsheet provides detailed information on chemical resistance and appropriate management strategies.
GRDC Insecticide resistance management and invertebrate pest identification factsheet provides information on green peach aphid and integrated pest management.
GRDC Aphids and viruses in pulse Crops factsheet provides general information on aphids and their management.
We thank Drs Paul Umina and Garry McDonald (PestFacts south-eastern) and Kym Perry and the PestFacts SA & Western Victoria (SARDI) team for preparing much of this article, after wide consultation with:
Brett Atkin – Agronomist, Elders (Victorian Mallee)
Greg Baker – Entomologist, SARDI (Adelaide)
Jenny Davidson – Plant Pathologist, SARDI (Adelaide)
David Eksteen – Agricultural Consulting (NSW Riverina)
Angela Freeman – Senior Research Scientist, VicDEPI (Victorian Wimmera)
Mohammad Aftab – Research Scientist – Virology, VicDEPI (Victorian Wimmera)
Frank Henry – Plant Pathologist, VicDEPI (Victorian Wimmera)
Don McCaffery – Technical Specialist (Pulses & Oilseeds), NSW DPI (NSW Central Tablelands)
Andrew McMahen – Agronomist, Landmark (Victorian Mallee)
Adam Pearce – Agronomist, Clovercrest Consulting (Victorian Wimmera)
Joop van Leur – Plant Pathologist, NSW DPI (NSW North West Slopes & Plains)
Kate Wilson – Agronomist, AgriVision Consultants (Victorian Mallee)
Matthew Whitney – Agronomist, Dodgshun Medlin (Victorian Mallee)