FARMERS are being encouraged to assess the extent of blackleg disease in canola crops this spring to reduce the risk of disease next year and beyond.
Blackleg is a sexually reproducing pathogen that will overcome cultivar resistance genes and is more severe in areas of intensive canola production.
Oilseeds disease authority Steve Marcroft, Marcroft Grains Pathology, said that to assess disease levels in current crops, samples could be taken any time from the end of flowering to windrowing (swathing).
“Pull 60 randomly chosen stalks out of the ground, cut off the roots with a pair of secateurs and, using reference photos in the GRDC fact sheet, estimate the amount of disease in the stem cross-section,” he said.
“Yield loss commonly occurs when more than 50 per cent of the cross-section of the cut stem is discoloured.”
To support growers in determining current disease levels, the Grains Research and Development Corporation (GRDC) has released the 2017 Spring Blackleg Management Guide Fact Sheet, developed by the National Canola Pathology team.
The guide outlines specific steps to manage blackleg and includes cultivar blackleg ratings and resistance groups for all canola cultivars including new cultivars which will be available in 2018.
The resource can help growers assess if they are in a high-risk situation and guide them to minimise future yield losses.
Dr Marcroft said that if growers identified that they were in a high risk situation, they should use management practices – outlined in the fact sheet – to reduce blackleg severity for coming seasons.
“They should also rotate between cultivars with different resistance genes to reduce the probability of resistance breakdown and reduce disease severity,” he said.
Dr Marcroft said that if growers identified that they were in a low risk situation and had not identified yield loss due to blackleg infection when assessing their crop, they should continue with their current management practices.
As well as advising growers to monitor canola crops in spring to determine yield losses in the current crop, the GRDC 2017 Spring Blackleg Management Guide Fact Sheet advises:
- To never sow your canola crop into the previous year’s canola stubble.
- Sowing at least 500m from the previous year’s stubble will reduce blackleg severity.
- To choose a cultivar with adequate blackleg resistance for your region.
- That relying only on fungicides to control blackleg poses a high risk of fungicide resistance.
That if monitoring has identified yield loss and you have grown the same cultivar for three years or more, to choose a cultivar from a different resistance group.
To further assist growers in determining the level of risk in their area, the GRDC’s National Variety Trials (NVT) Online website provides the latest information from blackleg monitoring sites across Australia.