JUST after news the fungicide Prosaro had been registered for use on canola for the treatment of blackleg, leading canola pathologists have issued a warning to growers not to rely on the spray too heavily.
Prosaro is the first foliar fungicide to be registered for use in canola, and it has been cautiously welcomed by blackleg experts, but they have warned against an over-reliance on the product.
Steve Marcroft, of Marcroft Grain Pathology, said Prosaro would be welcomed as an option against heavy blackleg infestations, but warned that overuse could lead to resistance issues.
Dr Marcroft said in order to ensure the industry’s long-term access to Prosaro, which can be used up to the 4-6 leaf stage, care must be taken.
As well as considering the return on investment he unnecessary applications could eventually lead to potential resistance issues.
“Growers need to be confident that they will incur significant yield losses before investing in this form of control.”
“If they are growing a cultivar with low blackleg resistance in a high risk situation, applying a foliar fungicide is an additional control option worth considering.”
Dr Marcroft said it can be difficult for growers to determine from a visual assessment as to whether a significant impact on production was likely to result from blackleg.
To assist growers in their assessments and management strategies, the GRDC has just released a new Blackleg Management Guide Fact Sheet.
Key management points include: Monitoring crops to determine yield losses in the current crop Choosing a cultivar with adequate blackleg resistance for your region Never sow a canola crop into last year’s canola stubble Relying only on fungicides to control blackleg poses a high risk of fungicide resistance If monitoring has identified yield loss and the same cultivar has been grown for three years or more, choose a cultivar from a different resistance group.
“It is important for growers to monitor crops each season so they know the extent of blackleg infection and can make more informed management decisions,” Dr Marcroft said.
The risk of blackleg infection in crops and potential for yield losses this year is severe due to the increased area sown to canola in 2011 and another large planting this year due to favourable oilseed prices.
Blackleg is the most severe disease of canola in Australia. Because it survives on canola stubble, last year’s expansive crop has heightened the risk this season.
Dr Marcroft said sowing canola on canola could result in the fungal pathogen overcoming cultivar resistance genes, resulting in many cultivars being destroyed and risking the long-term viability of the canola industry.