How do contact herbicides differ from translocated herbicides?

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.

Herbicides are categorized based on how they interact with weeds and other unwanted plants. The primary difference between contact and translocated herbicides lies in their mobility within the plant:

Contact herbicides: These agents, such as sulfuric acid, diquat, and paraquat, kill only the specific plant organs that they physically touch. They do not move through the plant's internal systems to affect other parts.1
Translocated herbicides: These agents, such as amitrole, picloram, and 2,4-D, are absorbed by the plant and transported from the site of application—typically aboveground surfaces or the soil—to other parts of the plant, including the roots. This systemic movement allows them to be effective against organs that were not directly sprayed.1

Understanding these mechanisms is essential for effective weed management, as the choice between a contact or translocated agent depends on whether the goal is to destroy surface growth or to eliminate the entire plant system, including the root structure.1