Herbicide injury is often categorized by mode of action, or the general way that an active ingredient kills a plant. Because active ingredients with the same mode of action affect the plant in the same general way, symptoms of herbicides within a mode of action are often similar.  Therefore, mode of action is a useful way to classify symptoms. The first seven modes of action, their effect on plants, and expected symptoms for grasses and broadleaf plants are described in the following pages. When the mode of action has not been classified, it is referred to as an unknown mode of action.

Mode of Action List

  • Lipid Synthesis Inhibitors 
  • Amino Acid Synthesis Inhibitors 
  • Seedling Growth Inhibitors
  • Synthetic Auxins
  • Photosynthesis Inhibitors
  • Cell Membrane Disruptors
  • Pigment Inhibitors
  • Unknown

Symptoms of Injury

Select a symptom below that best fits your plant and continue through the key until you determine which mode of action may be causing the symptoms.