South Perth, Western Australia
May 1, 2008
The Department of
Agriculture and Food blackleg disease model is predicting
that many early sown canola crops this year will escape serious
infection with blackleg – one of the most destructive diseases
of canola.
Department research officer Moin Salam said the blackleg disease
model, known as Blackleg Sporacle, could assist in predicting
the release of blackleg spores from old canola residue, based on
climatic conditions.
Dr Salam, who developed the model, said Sporacle and models like
it were methods producers could use to assess the level of risk
in their crops.
“A disease model like this gives growers confidence to seed
canola in low risk situations without applying fungicide,” Dr
Salam said.
“This year the lack of summer rain and the good April rains have
delayed the priming of canola residue to release Blackleg spores
until after the bulk of the canola crop will have emerged in
most of the wheatbelt.”
He said this meant that seedlings were likely to escape the bulk
of the blackleg spore release when they were most susceptible.
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Department of
Agriculture and Food pathologist Ravjit Khangura |
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Dr Salam said that in the past
early summer rain in some districts had led to the release of
spores at the same time as crop emergence – the most critical
stage for canola to be inflected with the disease.
“Currently the Sporacle model shows that most areas have a low
potential risk for canola crops emerging in early May. The only
areas with a high risk for crop emergence coinciding with
blackleg spore release are the south Stirlings and south of
Scaddan areas,” he said.
“The potential risk for other traditional canola growing areas
will not be high until late May or early June. These would
include the Great Southern and Lake District,” Dr Salam said.
“This year there has been little or no priming of the canola
stubble to release blackleg spores, creating a unique window of
opportunity for growers to seed canola in late April/early May
with low risk of infection during that early susceptible stage
of the crop.”
Department pathologist Ravjit
Khangura (photo) said canola seedlings were more susceptible to
blackleg disease infection at the cotyledon to six leaf stage of
the crop.
“This year’s weather has provided the opportunity for growers to
substantially reduce the risk of blackleg infection by sowing
early and practicing good separation from previous canola
crops,” Dr Khangura said.
“By timing crop emergence to avoid the bulk of the blackleg
spore release from old residues, canola growers can reduce the
impact of the disease on the crop substantially,” she said.
Dr Khangura cautioned that although Sporacle was an aid in
predicting blackleg disease risk based on climatic conditions,
it did not take into account the amount or the age of the
residues in a district.
“Canola residues usually have exhausted their blackleg spore
release after three years if they remain on the surface. In
northern districts, where there have been very few canola crops
grown coupled with dry seasonal conditions in the last two
years, there is a very low risk,” she said.
Dr Khangura said growers still needed to consider their own
situations where the risk was determined by three primary
factors:
• the blackleg rating of the canola variety;
• proximity to previous canola crops; and
• timing of crop emergence.
“If growers address all three of these factors, they will be
well on the way to managing blackleg in canola,” she said.
Growers can check the potential risk for blackleg in their
district by accessing Sporacle on the department’s website at
agric.wa.gov.au/cropdisease and also refer to ‘Managing Blackleg
Bulletin 4571’ for the details on blackleg management in canola. |
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