Understanding herbicide modes of action
Weed scientists at Kansas State University recently updated a comprehensive publication on herbicide mode of action. This publication, C715 - Herbicide Mode of Action, provides an in-depth description of how herbicides work to control weeds. Interspersed throughout the publication are helpful illustrations, definitions of herbicide terminology, and full color photos depicting various plant responses to herbicide applications (Figure 1).
The way in which a herbicide kills weeds is called its mode of action. Herbicide mode of action is a term that generally describes the plant process (e.g., photosynthesis) or enzyme (e.g., ALS) that is disrupted by the herbicide. Herbicide site of action refers to the specific biochemical or biophysical process in the plant that the herbicide disrupts to interfere with plant growth and development processes. This means that one mode of action may be associated with multiple sites of action. The term “herbicide mode of action” is sometimes used interchangeably with “herbicide site of action” or “herbicide mechanism of action.” Within a mode of action, herbicides may also be grouped by their chemical structures. Herbicides that share similar structures are said to be in the same chemical family.
The publication is divided into the following topic areas:
- Plant characteristics affecting weed control
- Environmental characteristics affecting weed control
- Application variables affecting weed control
- Categorizing herbicides
- Non-herbicide stresses
Understanding how herbicides work provides insight into how to use the chemicals and helps diagnose causes of poor weed control or crop injury.
Herbicide Mode of Action –C715 is available to download for free at: https://bookstore.ksre.ksu.edu/pubs/C715.pdf.
Figure 1. Sample page from the publication, "Herbicide Mode of Action", that discusses herbicide categories. Illustrations and herbicide terminology definitions are helpful resources that complement the text. Source: C715 - Herbicide Mode of Action, K-State Research and Extension.
Sarah Lancaster, Extension Weed Science Specialist
Mithila Jugulam, Weed Physiology
Jeanne Falk Jones, Multi-County Specialist, Colby