Britannica Sources used in this answer

Why can repeated use of one herbicide lead to herbicide-resistant weeds?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

weeding — weed Weeds being removed by hand from a parsley patch.

Repeated use of a single herbicide can lead to the development of herbicide-resistant weeds through the process of natural selection. When a specific herbicide is applied consistently, it eliminates susceptible plants, but any individual weeds that possess natural genetic variations allowing them to survive the treatment are left behind.1

These surviving weeds then reproduce, passing their resistant traits to the next generation. Over time, the population of weeds in the area shifts, becoming dominated by these resistant individuals, rendering the herbicide ineffective. Mechanisms of this resistance can include:1

Genetic mutation: Changes that lead to the overexpression of the target enzyme (such as EPSP synthase) or prevent the herbicide from interacting with that enzyme.1
Reduced uptake: Mutations that result in the plant absorbing or retaining less of the herbicide.1

To mitigate this risk, it is essential to practice responsible land management by utilizing multiple, diverse weed-management strategies rather than relying on a single chemical agent.2