The arguments for and against placing a symbol containing a letter to denote the mode of action on herbicide labels in Europe are reviewed. There is no clear view within and between the organizations that may influence the decision. However, it is generally accepted that such an initiative only should be part of an integrated approach to prevent the development of herbicide resistance in weeds.

A classification of herbicides according to their sites of action was developed to help maintain the usefulness of herbicides as a tool in crop production to delay the selection of herbicide-resistant weeds. The classification includes a numbering system for the site of action, the chemical family, and the common name of the herbicide. The United States of America trade name and package mixes also are included.

The classification of herbicides by site of action, published in 1997, has been revised. The classification system uses a numbering system for a herbicide's site of action, chemical family, and common name. Regulatory agencies in the United States and Canada have published labeling guidelines based on the classification to aid in herbicide resistance management.