Which type of weeds are most effectively controlled by contact herbicides?

Contact herbicides work by affecting only the plant parts they come into direct contact with, making them particularly effective on annual weeds. Annual weeds complete their life cycle in one growing season, which means they are often smaller and more susceptible to rapid defoliation when treated with contact herbicides. Since these weeds do not have established root systems that can absorb systemic herbicides, the impact of a contact herbicide can quickly eliminate the foliage and prevent the plants from maturing.

Biennial and perennial weeds often have more extensive root systems and foliage that can sometimes shield parts of the plant from the herbicide, making contact herbicides less effective on them. Biennial weeds, which have a two-year life cycle, may have more robust structures in the second year, and perennial weeds can regrow from their root systems, allowing them to recover even after being initially targeted by a contact herbicide. Therefore, while contact herbicides can impact all types of weeds, they are best suited for the management of annual weeds due to their life cycle characteristics and the rapid action needed for effective control.