Diagnosing group I herbicide damage in cereals

Group I herbicides are used for broadleaf summer weed control or selective broadleaf weed control in cereals.

Flag leaf is fused to resemble an onion leaf
Transient limpness in barley from dicamba spray
2,4-D induced stem distortion and awns caught in the leaf sheath
Distorted wheat heads
Chemical name Example trade name Chemical name Example trade name

Phenoxy acid

Pyridines

2,4-D amine

Amicide Advance®

Clopyralid

Lontrel®

2,4-D ester

Estercide Xtra 680®

Triclopyr

Garlon®

MCPA amine

Agritone 750®

Fluroxypyr

Starane®

MCPA ester

LVE MCPA®

Picloram

Tordon®, Grazon®

MCPB

MCPB®

Benzoic acids

2,4-DB

2,4-DB®, Buttress®

Dicamba

Banvel®

 

What to look for

    Paddock

  • Soil type related areas of poor crop germination resulting from Group I herbicide soil residual. This is rare.
  • Uniform areas of distorted plants.

    Plant

  • Foliar symptoms appear within 3 to 4 days of application. Susceptible plants start to twist and appear distorted.
  • Very early sprayed plants have a fused flag leaf that resembles an onion leaf.
  • Dicamba affected plants may briefly be wilted and prostrate.
  • Leaf mottling that is not always obvious.
  • Distorted heads that may have less grain.

What else could it be

Condition Similarities Differences
Diagnosing downy mildew in cereals Head distortion Downy mildew is restricted to wet areas
Diagnosing seed gall nematode Head distortion Seed gall nematode causes seeds to be replaced by small black galls

Where did it come from?

Dry soil
Dry soil
Time of herbicide application
Time of herbicide application
  • Herbicide breakdown in the soil is reduced when the soil is dry.
  • Germination damage is less likely with no-till sowing.
  • Very early spraying (2 to 4 leaf stage depending on variety) causes onion leaf deformation.
  • Spraying during the reproductive stage (approximately from flag leaf emergence to firm dough stage) causes head deformation and grain damage.

Management strategies

Time of herbicide application
Time of herbicide application
  • As a precaution, spray when the risk of drift is low.

See also

Where to go for expert help

Page last updated: Wednesday, 19 August 2015 - 9:07am