Growers planning on planting dual-purpose canola this spring are encouraged to keep a close eye on aphids and viruses over the summer and, if necessary, take appropriate action to limit their spread into autumn-sown canola crops.

Field surveys conducted across southern Victoria in 2016 and 2017 by Agriculture Victoria indicated viruses such as turnip yellows virus (TuYV), cauliflower mosaic virus (CaMV) and turnip mosaic virus (TuMV) were widespread in spring-sown canola.

Of the crops surveyed, averaged across both years:

• 92 per cent of crops surveyed showed an in-crop infection rate of 50 per cent for TuYV;
• 58 per cent of crops surveyed had an in-crop infection rate of eight per cent for CMV; and
• 58 per cent of crops had an in-crop infection rate of three per cent for TuMV.

Green peach aphid is the principal vector of TuYV, while the cabbage aphid and turnip aphid can also transmit viruses at a lower rate.

Agriculture Victoria regional research agronomist Frank Henry says the second year of monitoring presented more evidence to suggest there were aphids travelling from spring-sown canola into newly established autumn-sown crops.

"Turnip yellows virus is considered the most important virus in south-eastern Australia due to its high incidence, wide host range and persistent transmission," Mr Henry says.

"Autumn is the critical period for virus infection because aphids invade crops from weed hosts and self-sown canola, and canola is more susceptible to yield loss at seedling stage.

"Therefore, dual-purpose canola crops growing over the summer period are considered to be a high-risk management option for viruses as they provide a green bridge for infection of autumn crops.

"Although spread of viruses into autumn-sown canola was not detected in 2016, probably due to the dry summer and autumn conditions, risk of transmission would increase under conditions more conducive to aphid survival over summer with rainfall up to decile 8 to 9.

"Risk of transmission also increases when these conditions are combined with autumn temperatures favourable to aphid multiplication, such as those experienced during 2017 when there was a 56 per cent in-crop incidence."

Mr Henry says the incidence of virus in spring-sown canola also presents issues for forage brassicas grown over summer in southern Victoria.

"More evidence is required to quantify what kind of dry matter yield losses are occurring in forage brassicas as a result of virus infection, but we suspect it is having an impact," he says.

More information: Frank Henry, 03 5573 0975, frank.henry@ecodev.vic.gov.au