Diagnosing group B herbicide damage in field peas

Sulfonlyureas, imidazolamines and sulfonamides are systemic herbicides that are used for pre and/or post emergent grass and/or broadleaf weed control in cereals and are mostly highly toxic to peas. Damage can be caused by soil residue or spray contact. Imazamox and imazathapyr are used for post emergent broadleaf weed control in peas.

 

Affected plants are stunted with reduced root systems
Chlorotic new growth that becomes necrotic
Excessive new shoots form to compensate for growing point death
Sulfonylureas (SU's) Imidazolinones (IMIs)
Chemical name Example trade name Chemical name Example trade name
Trisulfuron Logran Imazapyr Arsenal
Chlorsulfuron Glean Imazapic Flame
Sulfosulfuron Monza Imazamox Raptor
Metsulfuron Hussar Imazethapyr Spinnaker
Iodosulfuron Ally Imazapic+Imazapyr Intervix
Mesosulfuron Atlantis Imazapic+Imazapyr+MCPA On-Duty
Sulfonamides    
Fumetsulam Broadstrike  

 

Metosulam Eclipes    
Furasulam Conclude    
Pyroxulam Crusader    

 

What to look for

    Paddock

  • Residual herbicide damage shows as stunted plants with pale to yellow new leaves.
  • Residual damage is more likely on more alkaline (sulphonylureas) or acidic (imis) soils
  • Spray tank contamination causes similar damage that is more uniformly distributed but varies with spray coverage on overlaps or boom turns.
  • Spray drift damage is usually worse near the source, with similar symptoms

    Plant

  • Soil residual herbicide damaged plants germinate normally but are stunted with pale to yellow new leaves. Red colours may develop on leaf edges/underside, stems and tendrils.
  • Discoloured areas develop brown necrotic spots and the plant slowly dies.
  • Plants are severely stunted with shortened stems, tendrils and petioles.
  • Excessive new shoots form to compensate for growing point death.
  • Seedling lateral roots are severely stunted.
  • Plants sprayed at later growth stages develop similar symptoms to new growth, and may take weeks to die.

What else could it be

Condition Similarities Differences
Diagnosing virus damage in field peas Clorotic young growth Patchy distribution not associated with a soil type or spray application..
Diagnosing glyphosate damage in field peas Chlorotic young growth then death. Plants die within 7-10 days.
Diagnosing manganese deficiency in field peas Chlorotic young growth, necrosis. Leaf interveinal chlorosis and tendrils roll inwards and die back from the ends. Plants do not die.
Diagnosing sulphur deficiency in field peas Chlorotic young growth. Varies with soil type, plants are not stunted and do not die.
Diagnosing iron deficiency in field peas Chlorotic young growth. Varies with soil type, plants are not stunted and do not die.

Where did it come from?

  • Chemical breakdown in soil is inhibited by high pH for sulfonylureas and low pH for imidazolinones.
  • Stressed plants are less able to metabolise herbicides and therefore more susceptible to damage. Stressors include drought, cold, wet weather, waterlogging, deep sowing, frost, nutrient deficiency and soil compaction.

How can it be monitored?

  • It is important to observe withholding periods for these herbicides to avoid damage to following crops.

Further information

Where to go for expert help

John Moore
+61 (0)8 9892 8476
Page last updated: Wednesday, 13 May 2015 - 1:51pm