Diagnosing group C herbicide damage in canola

A range of group C herbicides are registered for use in triazine tolerant (TT) varieties, but other varieties are susceptible to both pre and post emergent applications.


Leaf necrosis moves from leaf edges to veins

What to look for


  • Pale and/or scorched plants.
  • Direct spray damage is uniformly distributed but varies with spray coverage on overlaps or boom turns
  • Residue affected plants will be worse on soils that are wetter, sandier, lower in organic matter or more alkaline.


  • Plants emerge normally but paleness then death of the oldest leaf occurs. Necrosis on leaves progresses in from the leaf edges to the veins.

What else could it be

Condition Similarities Differences
Diagnosing potassium deficiency in canola Older leaf necrosis from edges Plants have puckered leaves and seedlings rarely show these symptoms. Damage varies according to soil type

Where did it come from?

Wet conditions
Wet conditions
Herbicide treated soil
Herbicide treated soil
Low organic matter
Low organic matter
  • These herbicides are more active in moist soil. More damage is likely after heavy rainfall, particularly in shallow duplex soils that are more easily waterlogged.
  • Situations where the herbicide is close to seed. This includes shallow sowing or heavy rain washing herbicide into furrows in ridged seedbeds.
  • Topsoils with low adsorption capacity such as sands with low organic matter.

How can it be monitored?

  • It is important to observe withholding periods for these herbicides to avoid damage to following crops.
  • Take care when spraying not to spray non-tolerant varieties.

Where to go for expert help

Page last updated: Wednesday, 4 February 2015 - 11:24am