FOR canola growers, blackleg was a concern in 2022 and while it was generally well-managed, apprehension was higher due to the increase in hectares seeded.
However, any lack of effect from fungicides was almost certainly due to heavy spore showers coinciding with seedling emergence and an extended wet spring - rather than reduced sensitivity or resistance.
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A lot of canola had been planted in the Esperance area over the past few seasons, which increased the inoculum level in the system and reduced rotation time between canola crops.
The wet conditions really gave it a good year and those high inoculum loads will remain on the stubble for 2023.
The blackleg pathogen adapts quickly to genetic resistance in canola varieties and rotating varieties from different resistance groups is key to keeping blackleg levels low.
Department of Primary Industries and Regional Development research scientist Andrea Hills said growers in the Esperance port zone like open-pollinated canola for seed production.
"However, there is a high risk of resistance breakdown if the same variety is grown and sown more than three years in a row," Ms Hills said.
"Choosing a variety with major effective gene resistance will also provide good protection against upper canopy infection (UCI) of blackleg, although that will decline over time.
"It is imperative not to plant canola into last year's canola stubble and to provide good distance between each year's plantings of the same variety."
The Grains Research and Development Corporation's Blackleg Management Guide and the BlacklegCM decision tool are essential sources of information for selecting canola cultivars by their resistance grouping and assessing other risk factors.
The Blackleg Management Guide recommends inspecting canola for crown cankers at the end of every season and changing to a variety from a different resistance group if the disease appears to be gaining ground.
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Along with regular crop and variety rotations, time of sowing will support blackleg control.
Early sowing reduces the risk of crown cankers, especially when combined with a fungicide seed treatment.
However, early sowing increases the risk of UCI if the crop starts flowering in June or July.
"UCI is unlikely to cause a yield loss in a crop that flowers from August, so early sowing should be combined with a slow maturing variety to avoid flowering in July," Ms Hills said.
"If UCI occurs, fungicide may not provide an economic benefit where projected yields are less than 2.0 tonnes per hectare.
"Growers in the high-rainfall zones can achieve higher yields and should use the UCI BlacklegCM app to determine if spraying will provide a benefit."
Australia's canola industry has not suffered any major blackleg losses for more than two decades, despite the highly virulent and mutable nature of the pathogen.
Regular variety rotation coupled with integrated disease management and strategic fungicide use have all helped contain the disease, despite an exponential increase in plantings and inoculum loads.
For disease-wary growers in the Albany and Esperance port zones, the guidelines for canola could well be applied to their barley and wheat variety programs for future seasons.
