CANOLA pathologist Steve Marcroft says rates of aerial blackleg in the oilseed crop have been steadily worsening over the past four years to a stage where yield damage is likely to be worse than from the disease in its soil-borne form.
However, the good news is that he believes a slight tweak in management practices will be able to significantly cut down the threat of the air-borne disease which damages flowers and pods.
“It seems to be that earlier flowering is placing a really high disease pressure on the crop,” Dr Marcroft told the crowd at Southern Farming Systems’ Agri Focus field day near Lake Bolac in Victoria last week.
He said farmers’ major concern with canola over the past 15 years had been in avoiding heat shock or moisture stressed caused by the springs cutting out.
However, this has had the unforeseen result of pushing flowering periods a little too early.
“Canola has been planted earlier and earlier, I think what we are seeing here is that envelope being pushed that bit too far,” Dr Marcroft, who runs a business, Marcroft Pathology, said.
“When you start seeing the crop flowering in July then it just puts the plants under a lot of disease pressure.”
He said research conducted by John Kirkegaard of CSIRO found the optimum time for flowering to start for canola in southern regions, where the vast majority of the crop is grown, is from the last week of July to the third week of August.
“This means farmers do not have to push back planting too significantly to boost their disease resistance.”
Dr Marcroft said the problem of aerial blackleg had been growing over the past few seasons, even though it has only made headlines this year.
“This is not something that has just emerged because of the wet season, we have been noticing the rate of infection rise over probably the past four seasons.”
Dr Marcroft said the level of damage was caused by where the infection occurs.
“It can occur on an isolated flower which then doesn’t pod up or it can go further down the plant, causing more widespread damage.”