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.
What to look for
- 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
- 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.
What else could it be
|Diagnosing blackleg in canola||Sudden seedling death, hypocotyl pinched-off||Blackleg does not affect roots. Lesions with black fruiting bodies present on cotyledon and leaves.|
|Diagnosing false wireworm||Sudden seedling death||If its false wireworm there would be chewing damage on hypocotyl, petioles, leaves|
|Diagnosing vegetable beetle damage||Sudden seedling death||If its vegetable beetle there would be chewing damage on hypocotyl, petioles, leaves|
|Diagnosing group B herbicide damage in canola||Orange-red cotyledons||Damping off symptoms also include distorted growing points, no hypocotyl or root pinching-off and rapid death.|
|Diagnosing waterlogging in canola||Reduced germination, orange-red cotyledons||Damping off symptoms also no hypocotyl or root pinching-off and rapid death.|
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.
- 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
Where to go for expert help
Page last updated: Thursday, 16 April 2015 - 1:16pm