Broad disease constraint resources are outlined in the Agronomists Toolkit. Specific disease categories are listed below:

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Downy mildew

Constraint - Downy mildew

Description

  • A fungal disease that affects foliage of canola and is both seed and soil borne 

  • It is favoured by cool wet conditions when leaves are in contact with the soil or other leaves

  • Rarely found beyond the rosette stage

Symptoms

  • Yellow areas on the upper leaf surface of young seedlings are the first symptoms

  • A white powdery fungal growth can be seen on the underside of the leaf beneath these spots

  • Individual spots join to form large irregularly shaped blotches that die and cause a large part of the leaf to dry out, with the upper surface becoming yellow-red

  • Infected cotyledons die prematurely

  • Severely affected plants may be stunted

Damage

  • Downy mildew does not usually affect yield so control measures are not generally warranted unless plant densities are severely reduced on a regular basis

Management

Crop rotation, using clean seed, and the control of cruciferous weeds between canola crops can reduce disease severity. In areas where downy mildew is a severe problem fungicides containing copper as the active ingredient are registered for use in Australia.

 

Links and Resources

DAFWA - Diagnosing downy mildew in Canola

Introduction, what to look for in paddock and plant, where did it come from, and management strategies. Page last updated 2014.

DEPI VIC - Canola diseases. Downy mildew

The section on downy mildew contains introduction, symptoms, disease cycle, and management. Published 2008, page last updated 2009, reviewed 2010.

DEPI VIC - Identification and management of field crop diseases in Victoria. Downy mildew

Page 146. Table 11.1 gives a key for canola diseases at different stages of plant growth. Downy mildew is referenced. Page 153. Contains information on introduction, symptoms, disease cycle, and management. Published 2012.

GRDC - Best Practice Management Guide. Downy mildew

Page 65. Introduction, symptoms, disease cycle, and management.  Page 59. Table of common disease of canola. Published 2009.