Herbicide resistance is the inherited ability of a biotype of a weed to survive an herbicide application to which the original population was susceptible. A biotype is a group of plants within a species that has biological traits (such as resistance to a particular herbicide) not common to the population as a whole. In simple terms, resistance refers to a situation where a given herbicide, applied at the recommended rate and time, once controlled a particular weed population but, after repeated use, that herbicide no longer controls that population. That population is said to be resistant (or resistance has developed in that population).
For a complete explanation of how a population of weeds becomes resistant to an herbicide see Understanding Resistance. Wherever herbicides are used on a consistent basis, it is important to recognize the difference between weed population shifts, and resistance. Both weed population shifts and resistance are undesirable and make weed management difficult. To explore important terminology visit the Herbicide Resistance Terms to Know page. For information on the number of resistant weed species and their worldwide distribution see weedscience.org.
Herbicide resistance is described in detail by breaking the topic into the sections listed below. All content has been expertly reviewed by Drs. Carol Somody and Les Glasgow, Syngenta.
Topics Included in this Module
- Herbicide Resistance Terms to Know — Understand the difference between population shift and resistance as well as other concepts.
- Is Herbicide Resistance to Blame? — Resistance is not the only cause of weed control failure
- Incidence and History of Herbicide Resistance — Resistance to one or more of 25 herbicide families has been observed in the U.S.
- Mechanisms of Herbicide Resistance— How does resistance develop in a population?
- Proactive Herbicide Resistance Management — Methods to help slow or prevent the development of herbicide resistance.
- How to Manage Herbicide Resistance — What you can do if resistance is already a problem
- Herbicide Spraying by the Numbers — Use information on pesticide labels to rotate herbicide “families”
- Resources and Suggested Reading — Additional information about herbicide resistance.
Compiled by Wayne Buhler, PhD