Herbicide Mode of Action Important to Weed Resistance Management

Herbicide mode of action is a key component of weed control.   Image:  Man kneeling in corn field.

More Modes are Merrier for Weed Control

Herbicide resistance has been found in nearly 150 weed species in the United States. Creating a weed-control plan that can handle resistant weeds and avoid further resistance development requires careful herbicide selection. The goal is to maintain diversity in herbicide mode and site of action.

Currently, 102 herbicide active ingredients fall into 10 primary modes of action, as classified by the Weed Science Society of America. Mode of action (sometimes called mechanism of action) refers to how the herbicide affects plant growth. Site of action refers to the specific plant enzyme or biochemical process that is affected by the herbicide. Repeated use of herbicides with the same mode of action causes selection pressure that leads to an increase in herbicide-resistant weed populations, so aim for incorporating products with multiple modes of action.

A herbicide classification chart (PDF) is a helpful tool for planning an effective resistance management program. And best practice is to keep detailed field records of:

  • Scouting dates and weeds present
  • Herbicide names and dates applied
  • Herbicide mode of action and group numbers
  • Weeds not controlled by herbicide applications (and don’t let these weeds go to seed)

When developing a season-long herbicide program, tank mixes or premixes containing herbicides that have two or three modes of action will deliver the most reliable control, while helping to prevent the spread of herbicide-resistant weeds. Avoid using the same single herbicide mode of action more than twice in a season, since it could cause significant selection pressure within weeds.

Many DuPont herbicides offer multiple modes of action in one premix. Here are a few examples:

  • DuPont™ Trivence® herbicide provides three modes of action (Groups 2, 5 and 14) to help tackle the toughest broadleaf weeds, keeping soybean fields clean well after planting and supporting uniform crop emergence.
  • DuPont™ Envive®, Enlite® and Afforia® herbicides feature two modes of action (Groups 2 and 14) for consistent control of challenging weeds in soybeans, including winter annuals, dandelion, lambsquarters and other glyphosate- or ALS-tolerant or resistant weeds.
  • For early weed control in corn, DuPont™ Prequel® herbicide uses two modes of action (Groups 2 and 27) to provide burndown and residual weed control, and improve effectiveness on glyphosate- or ALS-tolerant or resistant weeds.

Finding the best combination of products can be challenging, so it pays to work with a team of experts who know your local conditions, weed pressures and operational goals. They can help you determine the most effective and affordable crop protection program.

The information provided on this website is for reference only. Always refer to the product labels for complete details and directions for use.