Diagnosing Group I herbicide damage in canola

Group I herbicides are used for broadleaf summer weed control or selective broadleaf weed control in cereals. Damage can be caused by soil residues or spray contact.

Sprayed plants have thickened crowns, stems and petioles and twisted, distorted petioles and leaves
Twisted stems and curled, split pods from spray drift after flowering
Stem kinking and thickening in early (above) and late growth
Roots may develop nodules that can resemble club root
Phenoxy acid Pyridines Benzoic acids
Chemical name Example trade name Chemical name Example trade name Chemical name Example trade name
2,4-D amine

Amicide Advance®





2,4-D ester

Estercide Xtra 680®



MCPA ester










2,4-DB®, Buttress®



What to look for


  • Severely distorted plants
  • Direct spray damage is uniformly distributed but varies with spray coverage on overlaps or boom turns.
  • Spray drift damage is usually worse near the source, but ester vapour drift can cause widespread damage that can be apparently random due to swirling wind effects.


  • Rarely, herbicide residue damage causes poor emergence.
  • Sprayed plants have thickened crown, stem and petiole and twisted, distorted petioles and leaves.
  • Downward bending of the crown, stem and petioles.
  • Crown swelling may become enlarged and cracked reducing sugar and nutrient flow to the plant, and pale new leaves.
  • After stem emergence, stems bend then grow up causing a kink,
  • Herbicide drift after stem elongation causes twisting of stems and pods. Pods may abort or curl and split.

What else could it be

Condition Similarities Differences
Diagnosing turnip mosaic virus in canola Puckered generally light green leaves Turnip mosaic virus occurs as scattered affected plants or in small patches, rather than a directly sprayed or spray drift pattern.
Diagnosing clubroot in canola White nodules on roots Club root nodules turn brown and mushy, and the plant is wilted rather than distorted.
Diagnosing blackleg in canola Cracked stem canker at ground level Black leg cankers are dark inside and the plant usually lodges and dies.

Where did it come from?

Time of herbicide application
Time of herbicide application
Dry soil
Dry soil
  • The risk of spray drift is greater when there is a temperature inversion or windy conditions.
  • Germination damage is less likely with no-till sowing.
  • Herbicide breakdown in the soil is reduced when the soil is dry
  • Vapour drift of ester formulations can go for kilometres in warm conditions.
Page last updated: Monday, 15 June 2015 - 3:17pm