Transmitted by green peach aphid (GPA), the combination of virus and aphid feeding has caused considerable damage and crop losses in parts of South Australia and Victoria, and infection has also been detected in southern NSW.

GRDC managing director, John Harvey, says that in the early stages of the outbreak, initial identification of BWYV as well as testing of GPA populations for insecticide resistance was undertaken with support from existing GRDC investments. 

“In recognition of the severity and extent of this outbreak, the GRDC has now provided an additional injection of $315,000 as emergency funding,” Mr Harvey said. This funding will be used to:

Appoint part-time co-ordinators to conduct a forensic analysis of canola paddocks including management practices, aphid activity and weed levels that have contributed to the severity of the outbreak. 

The co-ordinators will also assist with collection of aphid samples for resistance testing in the systematic survey.

This information will be used to ensure best advice is available to limit potential damage in future years. This work will be led by Dr Jenny Davidson and Mr Greg Baker, of the South Australian Research and Development Institute (SARDI).

Co-ordinate communication to growers and advisers nationally to ensure they have the best information available to limit further damage. This will include presenting at regional field days and providing updates for e-newsletters.

The co-ordinator role in SA has also been assisted with an additional $40,000 in emergency funding provided by the South Australian Grain Industry Trust (SAGIT).

Undertake a preliminary assessment of virus levels in canola varieties to identify if there are any useful levels of resistance to BWYV for future sowing recommendations.

Collect aphid populations in the southern region in a targeted manner and test for resistance to key insecticide groups to determine effective options for ongoing aphid control in both canola and pulses.  This work will be led by Dr Paul Umina of cesar.

Mr Harvey said that through GRDC’s existing investments in virology, a number of activities will be undertaken to assist in further understanding of this BWYV outbreak. These activities will include:

Drs Angela Freeman and Mohammad Aftab, from the Department of Environment and Primary Industries Victoria, assessing the severity of BWYV in canola and pulses in spring, undertaking studies on vectors and host range of BWYV and continuing their work with the Department of Agriculture and Food Western Australia (DAFWA) on the development of a predictive model for BWYV in canola and pulses.

Dr Joop van Leur, of NSW Department of Primary Industries, leading a GRDC project to investigate viruses of canola and pulses in northern Australia, including the impact of BWYV in canola and its link to pulse crops such as chickpea.

Meanwhile, the onset of cold and wet weather has caused a general decline in the population and activity of GPA, large infestations of which in autumn and early winter have resulted in extensive crop losses and damage from BWYV. GPA is the principal vector of the virus.

Experts say that although aphid numbers have now decreased, crops could remain susceptible to yield loss from BWYV infection until the mid-podding stage. Greatest yield loss occurs if infection takes place at the rosette stage. Infection after mid-podding usually results in minimum yield loss but oil quality can still be affected.

GRDC Senior Manager Plant Health, Dr Ken Young, encourages growers to continue monitoring for aphids and to consult with their local agronomists in determining the need for treatment.

“Vigilance is critical, especially with a pest like GPA as populations can build rapidly and significant infection and crop damage can soon occur,” Dr Young said.

Growers should be prepared to apply insecticides in late winter or early spring to limit the spread of the virus once aphids start to become more active and begin their spring flights.  However, if a crop is already widely infected with BWYV then insecticides may not be warranted except to prevent direct feeding damage from aphids, which is very unlikely.

BWYV can be transmitted by relatively few aphids feeding on plants, and symptoms may not present themselves for up to five weeks post infection. Severe symptoms are likely to be caused by a combination of virus infection and aphid feeding damage. In addition to canola, pulse crops may also be at risk in spring.

In South Australia, up to 10,000 hectares of canola in the Lower North and Mid North regions has been severely damaged and a number of crops have had to be re-sown.

Virus-like symptoms have also been reported in canola crops in the Upper North, on Eyre Peninsula, upper Yorke Peninsula and in the upper South-East.

In Victoria, BWYV has been found in numerous canola crops in the Wimmera and Mallee, where some reports suggest that more than 50 pc of all canola crops are now infected. Unusually high BWYV autumn infections have also been detected in canola paddocks in New South Wales.

Experts believe the rainfall in February-March created a “green bridge” of weed hosts for BWYV and GPA and warm temperatures into early winter provided ideal conditions for aphid population development, flight activity and widespread colonisation of canola crops.

The presence of insecticide resistance in many GPA populations has compounded the situation. Studies funded by the GRDC have found that the extent of insecticide resistance in GPA across Australia has escalated as a result of heavy reliance on insecticides to manage grain pests, placing strong selection pressure on the insect to develop resistance and leaving growers with limited future control options.  A key part of this funding is to provide further information about which insecticides will be effective in controlling aphids.