Dr Steve Marcroft says fungicide tolerant blackleg
isolates can cause stem canker and therefore
potentially yield loss.
Southern region canola growers are being advised to read the GRDC’s current Blackleg Management Guide to be aware of all management options available to them in 2016 in order to reduce their reliance on fungicide seed treatment.
In 2015, a survey of 200 paddocks across Australia found that 15 per cent of paddocks screened for fungicide-tolerant blackleg isolates had a high tolerance to fluquinconazole, the active ingredient in seed treatment Jockey®.
It is currently unknown whether the fluquinconazole tolerant isolates have cross tolerance with the other commonly used blackleg fungicides. Jockey®, prothioconazole/tebuconazole foliar fungicide Prosaro® and triazole in-furrow fungicide Impact® In-Furrow are all from the same DMI fungicide group. Work will be undertaken during 2016 to determine if cross tolerance has occurred.
Blackleg is a sexually reproducing pathogen that will overcome cultivar resistance genes. Fungal spores are released from canola stubble and spread extensively via wind and rain splash.
The disease is more severe in areas of intensive canola production, such as South Australia’s lower Eyre Peninsula. Fungicide tolerant blackleg isolates can cause stem canker and therefore potentially yield loss.
Marcroft Grains Pathology principal Dr Steve Marcroft says there are a number of pre-planting measures growers can take to reduce the risk of blackleg and reduce their reliance on fungicide later in the season.
If crop monitoring in the previous year showed signs of blackleg and yield loss, Dr Marcroft says growers should look at their canola varieties’ blackleg rating and consider how close they sow their canola to the previous year’s stubble.
“Planting canola up to 500 metres away from the previous year’s stubble and growing varieties with blackleg resistance ranging from moderately resistant to resistant will reduce the risk of blackleg infection,” Dr Marcroft says.
He says the first indication of fungicide tolerance is likely to be lesions occurring on the cotyledons of seedlings grown from Jockey®-treated seed. If fluquinconazole is effective it should protect cotyledons from blackleg lesions. If fungicide tolerance is present the only in-season control option is Prosaro®, the only registered foliar fungicide.
Last year’s blackleg survey found that 14 per cent of the 50 paddocks surveyed from Victoria had a high tolerance to fungicide, while almost 16 per cent of the 44 samples submitted from South Australia had high tolerance to fungicide.
New South Wales recorded the highest level of fungicide tolerance, with 21 per cent of the 62 samples submitted showing high tolerance to fungicide. Western Australia was the lowest, with about seven per cent of the 42 samples submitted showing high tolerance.
“This was the first large-scale survey carried out on Australian populations to detect fungicide tolerance,” Dr Marcroft says. “Therefore, it is unknown whether this tolerance has increased, decreased or remained the same over years.
“However, since Jockey® has been used as a seed dressing for numerous years it is not surprising that tolerance was detected and is potentially increasing in frequency among canola plantings.”
Dr Steve Marcroft, firstname.lastname@example.org
View and download the GRDC's blackleg management guide
View and download the GRDC's canola GrowNote
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