Diagnosing group C herbicide damage in field peas

This category contains root pre-emergent Group C herbicides such as simazine and metribuzin that are routinely used in lupins, but damage field peas. Cyanazine and metribuzin are registered for pre-emergent weed control in field peas.

Metribuzin damage. Typically scorched ends/edges of older leaves and tendrils
Plants become stunted with scorched brown leaves
Triazines Triazinones

Chemical name

Example trade name Chemcial name Example trade name
Simazine Simazine Metribuzin Sencor
  Geasatop   Lexone
Atrazine Atrazine    
  Bladex 2    
Diuron Diuron    


What to look for


  • Pale and scorched seedlings with worse damage on sandier soils with low organic matter.


  • Seedlings emerge normally but tips, edges of older leaflets and tendrils become bleached, pale brown and shrivelled.
  • Necrosis moves to successively younger leaves, as the plant becomes pale and stunted, until it recovers or dies.

What else could it be

Condition Similarities Differences
Diagnosing seedling root rot in field peas Progressive necrosis and death of older leaves Necrotic discoloured roots
Diagnosing zinc deficiency in field peas Older leaf pale necrosis. Plants are less stunted have more inter-plant variability, and do not die.
Diagnosing potassium deficiency in field peas Older leaf pale necrosis. Pinkish necrotic spots rather than marginal necrosis; affects older plants
Diagnosing soil acidity in field peas Older leaf pale necrosis. Affects leaf patches rather than margins and is worse on usually lighter textured acidic soils. Roots are also stunted.

Where did it come from?

  • These herbicides are more active in moist soil.
  • Situations where the herbicide is close to seed. This includes shallow sowing or heavy rain washing herbicide into furrows in ridged seedbeds.
  • Damage is more common on 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.

Further information

Where to go for expert help

John Moore
+61 (0)8 9892 8476
Page last updated: Wednesday, 13 May 2015 - 2:06pm