Prolonged cool conditions recently have bolstered the progression of blackleg upper canopy infection (UCI) in canola crops across south eastern Australia.
Oilseeds disease expert Steve Marcroft of Marcroft Grains Pathology said the incidence of UCI this year had been widespread.
"Infection has been reported in canola crops from South Australia's Eyre Peninsula right across into Victoria and up through southern New South Wales," Mr Marcroft said.
"While blackleg UCI has become increasingly prevalent over recent years, its presence normally drops away as we move into August and temperatures start to rise.
"But this year the extended cool conditions have favoured the progression of the disease through to the start of flowering."
Many growers have been applying fungicides at around 30 per cent bloom to reduce UCI severity and yield losses.
Field experiments have shown that blackleg UCI, a term describing infection of flowers, peduncles, pods, upper main stem and branches, can cause yield losses of up to 30 percent.
The impact on yield varies depending on the timing of infection and plant part infected.
While the crown canker blackleg is well understood, the factors contributing to UCI and possible control strategies are currently under investigation through Grains Research and Development Corporation (GDRC) research investments.
It is now thought that UCI infections are also systemic, causing damage to the plant's vascular tissue, similar to traditional blackleg crown infections.
The issue for growers is that external symptoms may appear insignificant, but internal vascular damage may cause significant yield losses.
Preliminary results indicate this may be why fungicide applications on crops with few symptoms can still result in economic yield returns.
More information on blackleg UCI is contained in the GRDC Grains Research Update paper at bit.ly/2ZtbUVU.