Why is it recommended to kill all targeted weeds when using herbicides?

The recommendation to kill all targeted weeds when using herbicides is primarily rooted in the concept of preventing the development of herbicide resistance. When weeds are not completely eliminated, the surviving individuals may possess traits that allow them to tolerate or resist the herbicide used. Over time, these resistant weeds can reproduce and create a population that is increasingly difficult to control with that specific herbicide, leading to a cycle of reliance on stronger or different chemicals, which can have negative environmental impacts and increase management costs.

Ultimately, thorough control of targeted weeds promotes better long-term management strategies, ensuring that the effectiveness of herbicides is maintained and reducing the likelihood of resistant weed populations from emerging in the future. It emphasizes the importance of integrated weed management practices that not only rely on chemical controls but also incorporate cultural, biological, and mechanical methods to sustainably manage weed populations.