Leg-up for canola growers in minimising the risk of blackleg

Author: | Date: 21 Feb 2011

Leg-up for canola growers in minimising the risk of blackleg

Growers are being equipped with an important tool in their quest to minimise the risk of blackleg – the most damaging disease of canola and juncea-canola in Australia.

Industry experts and the Grains Research and Development Corporation (GRDC) have developed a Risk Assessor to help growers make the right choices prior to or at sowing this coming season in order to reduce the risk of blackleg.

Growers are encouraged to use the Risk Assessor to determine if a paddock presents a high risk situation and what practices can be changed to reduce yield loss caused by blackleg.

In some circumstances, the blackleg fungus Leptosphaeria maculans can cause up to 90 per cent yield loss.

Dr Steve Marcroft from Marcroft Grains Pathology at Horsham, Victoria, says the severity of blackleg is influenced by several factors and the effect of these factors varies between regions.

Dr Marcroft, who collaborated with GRDC is developing the Risk Assessor, says
blackleg is challenging to control because the pathogen:

• Survives on stubble, resulting in higher levels of spore release in intensive canola production regions
• Spreads via windborne and rain-splashed spores, resulting in inoculums being spread extensively and quickly
• Grows systemically within the plant, resulting in limited efficacy of foliar applied fungicides
• Reproduces sexually, resulting in diverse pathogen populations that can overcome resistance genes within a few years.

Dr Marcroft says that all blackleg management practices have to be implemented prior to, or at, sowing and that growers should follow three simple steps.

“The first step is to determine if your farm is in a high blackleg risk region. This can be achieved by using the table on the GRDC Blackleg Risk Assessor Fact Sheet,” he advises.

“The second step is to determine each paddock’s blackleg severity. This can be done by assessing the level of disease in a current crop.” The Fact Sheet details how to assess the level of disease.

“If growers have identified that they are in a high risk situation via the first two steps, they are then advised to determine which management practices can be changed to reduce the risk of severe blackleg infection.”

A table within the Fact Sheet helps in the estimation of how each management practice is likely to influence the risk of blackleg causing yield losses.

“By changing particular management strategies, the risk of blackleg in a paddock can be minimised,” says Dr Marcroft.

“For example, if the same cultivar of canola or juncea-canola has been grown for three years, switching to a different cultivar can reduce the risk.”

The Blackleg Risk Assessor Fact Sheet will be available at upcoming GRDC Grains Research Updates and is accessible via www.grdc.com.au/GRDC-FS-BlacklegRiskAssessor. It is also available free (plus postage and handling) through GRDC’s Ground Cover Direct – freecall 1800 110044 or email ground-cover-direct@canprint.com.au.