Contact and translocated products

Agrochemicals have two primary modes of action – either as contact or translocated (or systemic) actions.

Contact herbicides – such as propanil - are applied to foliage and other above-ground parts of a plant. They kill plant tissues at or very close to the application site. Thus, they generally need good coverage of the plant to be effective.

Translocated agrochemcials – such as 2,4-D and cyhalofop butyl - are absorbed by the plant roots or above-ground parts of a plant. Within the plant, the herbicides then move to and kill tissues that may be remote from the point of application but where herbicide action occurs. Thus, it is often less important with systemic of translocated herbicides (relative to contact herbicides) to have full coverage of the plant.

While some agrochemcials are systemic (or translocated), their action may be dependent on entry through a particular part of the plant – e.g., they may need to be taken up through the roots – or they may only be taken up through the leaves.