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A survey of 140 canola fields (Brassica napus) was conducted in August and September 2009, between the development stages of 10 - 60 percent seed colour change. Fields were surveyed in the four regions of Manitoba (Central, Eastern/Interlake, Southwest, Northwest) at targeted distance of 20 miles between each field. Visual disease assessments were made in each field based on a sample size of 100 plants. Sampling occurred in a W pattern, where 20 plants were collected at each ‘point’ of the W and points were 20 paces apart. The first sampling point was targeted to be 100 paces adjacent to the field entrance and 100 paces into the field.
Canola fields were assessed for the prevalence (percent crops infested) and incidence (percent plants infected per crop) of sclerotinia stem rot (Sclerotinia sclerotiorum), aster yellows (phytoplasma), foot rot (Fusarium spp. and Rhizoctonia sp.), blackleg (Leptosphaeria maculans), fusarium wilt (Fusarium spp.) and clubroot (Plasmodiophora brassicae). For sclerotinia stem rot, each plant was scored for both main stem and upper branch/pod lesions. Blackleg lesions that occurred on the upper portions of the stem were assessed separately from basal stem cankers. The prevalence and percent severity of alternaria pod spot (Alternaria spp.) was also assessed (Conn et al. 1990). In addition to the visual assessment of disease presence and incidence, sixty soil samples were collected representatively throughout the province for clubroot DNA analysis.
Results:
A number of diseases were observed in each of the four regions of Manitoba, but clubroot symptoms were not observed in any of the fields surveyed in 2009. Sclerotinia stem rot and blackleg were the most prevalent diseases throughout the province. Sclerotinia prevalence ranged from 100% in the Eastern/Interlake region to 81.3% in the Southwest region, with a provincial mean of 91.4%. Mean disease incidence ranged from 36.8% in the Eastern/Interlake to 7.2% in the southwest region with a provincial mean of 17.5%
Blackleg basal cankers were observed in 55.7% of the crops surveyed in 2009 with prevalence the highest in the Central and Eastern/Interlake regions at 75.5% and 75.0% respectively and the lowest in the Northwest region at 21.7%. Incidence ranged from 8.0% in the Central region to 1.7% in the Northwest region, with a provincial mean of 4.3%. The mean prevalence of blackleg stem lesions was also55.7 % with disease prevalence highest in the Central region at 75.5% and lowest in the Southwest at 39.6%. Incidence ranged from 7.2% in the Northwest region to 1.0% in the Southwest region, with a provincial mean of 3.5%.
The prevalence of alternaria pod spot in 2009 was 40.0%, with 46.9%, 85.0%, 21.7% and 22.9% prevalence in the Central, Eastern/Interlake, Northwest and Southwest regions respectively.
Aster yellows was observed on average in 15.0% of fields in the province. Fusarium wilt and foot rot were observed at low levels in almost all regions, with provincial mean prevalences of 3.6% and 2.1% respectively.
Preliminary results of 2009 Canola Disease Survey: (Click for detailed chart)
Are you interested in taking part in the 2010 survey?
Send the following information to Debbie Belanger;
Name, Town, Rural Municipality, Phone, E-mail
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