Diagnosing damping off in canola

Damping-off is seedling root and hypocotyl (seedling stem) disease that can be caused by a complex of Rhizoctonia, Fusarium and Pythium fungi.

Rhizoctonia affected seedlings develop red-brown hypocotyl lesions as shown by the middle seedling
Surviving plants are stunted
Dying plants turn yellow red
Seedlings affected with hypocotyl rot have thin wire-like stems with reddish-brown discolouration

What to look for

    Paddock

  • Areas of poor germination and collapsed dying seedlings.
  • More common in dry sown paddocks and those sown at the break of the season followed by poor conditions for germination and growth.
  • Rhizoctonia hypocotyl rot is more common in loose soils in cool dry conditions. Wet heavy soils favour Pythium root rot.
  • Cold damp soils favour Fusarium root rot

    Plant

  • Plants germinate but die after emergence.
  • Seedlings have pinched roots, collapse and die (Pythium, Fusarium, fungi).
  • Rhizoctonia affected seedlings develop red-brown hypocotyl ,lesion, become pinched off and collapse at ground level.
  • Orange-red colour then death of cotyledons and older leaves.
  • Affected plants that survive to the 3-4 leaf stage may remain stunted, and flower and ripen prematurely.

Where did it come from?

  • Damping-off fungi are soil-borne and survive in the soil by forming resistant resting structures when no host is present.
  • These resting structures germinate with the break of the season and the fungi grow through the soil until they find a susceptible host plant. Dry seeds become vulnerable to attack as soon as they begin to germinate.
  • Once in the plant, the fungi multiply causing decay that damages or kills the seedling. They are usually weak pathogens that are only able to infect young succulent tissue.
  • At the two to four leaf stage roots of canola plants become more resistant to further infections. Therefore, most damage occurs when wet and cold weather slows plant growth.
  • Temperature and soil moisture affect disease development. Loose, cold and dry soils favour Rhizoctonia solani, while cold damp soils favour Fusarium spp. and wet, heavy soils favour Pythium spp.

Management strategies

  • Yields are only affected when plant numbers are severely reduced or large patches are formed.
  • Damping-off fungi will germinate with the opening rains of the season. Once they have germinated they are very successfully controlled by soil tillage. If crops are re- sown the sowing tillage will generally control the fungi.
  • Seed fungicide treatments applied at sowing can reduce damping-off damage
Source URL: https://www.agric.wa.gov.au/mycrop/diagnosing-damping-canola
This print version was generated at 10:42am on the 14th of May, 2025.
The original document was last revised at Thu, 16/04/2015 - 1:16pm

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The Chief Executive Officer of the Department of Primary Industries and Regional Development and the State of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.