Herbicide Injury Diagnostic Key

Herbicide Injury Diagnostic Key
T. L. Trower and C. M. Boerboom

The following herbicide injury diagnostic key uses a three-step approach to separate our numerous herbicides into eleven modes of action.  Then, the herbicides within a mode of action can be investigated further to determine if one of them caused the injury.  The first step in the key is to determine when the injury symptoms first became evident; symptoms appearing during or immediately after crop emergence may indicate carry-over or preemergence herbicide injury while symptoms appearing after crop emergence points to a postemergence herbicide.  The second step is to determine if the injury was the result of a herbicide with contact activity or if the herbicide was translocated in the plant.  A contact herbicide affects the leaves that were treated while a translocated herbicide affects new leaves.  The final step in the key is to match the injury symptom to a herbicide mode of action.  The following table lists many of the most common situations that lead to crop injury.

Injury Symptoms Appear:
During or immediately after crop emergence

  • Herbicide carry-over
  • Misapplication- rate too high
  • Shallow seed placement
  • Wrong herbicide rate for soil type
  • Improper interval between herbicide application and planting
  • Excessive rainfall and cold soils
  • Improper herbicide placement or timing

After crop emergence

  • Drift
  • Tank contamination
  • Misapplication- rate too high
  • Incorrect additive/surfactant
  • High temperatures/humidity at application
  • Improper tankmix partner
  • Wrong herbicide

Begin Diagnosis