Big wet ups risk of canola disease
Cool wet conditions have placed canola at higher risk of Sclerotinia stem rot this year and growers are urged to monitor early flowering crops.
Department of Primary Industries and Regional Development plant pathologist Ravjit Khangura said Sclerotinia apothecia, the minute fungal fruiting structures of the disease, and basal stem infections had been reported in the northern and southern regions.
Stuart Slade, who has about 700ha of canola across three properties in Mount Barker, Kojonup and Moodiarrup, has been looking for Sclerotinia for a couple of weeks but is yet to find any.
He finds the fungus about every second year and all his varieties of canola appear equally susceptible.
“A lot of it is paddock history,” he said.
“We do a lot of trash management in burning and trying to smash up that stubble to kill the schlero inside.”
Dr Khangura said the best conditions for Sclerotinia spore release occurred three weeks before flower if more than 40mm of rainfall occurs with greater than 75 per cent humidity.
“For a significant level of stem infection to occur, these favourable conditions should continue at least for the next two to three weeks,” she said.
She said canola that had started flowering or was about to flower was most at risk and may require fungicide treatment.
Mr Slade said he would use a helicopter if he needed to spray his canola. He said the most significant cost was the chemicals, not the application, and the downward draft of the helicopters helped force the fungicide down into the canopy.
Dr Khangura said timing was crucial to an effective response; however the risk reduced if dry weather was forecast throughout flowering.
“If wet and humid conditions prevail a few weeks before flower and the forecast is for continuous showers for the next two to three weeks, growers are advised to spray their crops at 20-50 per cent bloom, if there is a history of Sclerotinia in the paddock and the surrounding paddocks,” she said.
Two spray applications should be considered if growers have high-risk paddocks, such as those with tight rotations, heavy soil types, a dense stand of canola or high rainfall areas where continuous wet conditions were forecast during flowering.
Dr Khangura said the return on investment from a single application of fungicide had varied between $40-$225 per hectare.
“However, late applications past 50 per cent bloom are off-label and not effective in controlling disease in most years,” she said.
Department of Agriculture and Food canola pathologist Dr Ravjit Khangura has undertaken research that shows that the timing of fungicide treatments to control Sclerotinia stem rot in canola is crucial to protecting yields.
Sclerotinia stem rot.