What is the primary action of contact herbicides?

Contact herbicides primarily function by directly affecting the plant tissues they come into contact with, leading to immediate cellular damage and plant death. These herbicides do not move through the plant systemically, meaning they do not travel to other tissues beyond the point of application. Instead, their effectiveness relies on thorough coverage and contact with the desired weeds. When applied correctly, contact herbicides quickly disrupt cellular processes and lead to visible injury or death in the target plants.

In contrast, other options involve different mechanisms. Systemic movement through plants pertains to systemic herbicides, which are absorbed by the plant and transported to various tissues to kill the plant from within. Inhibition of germination refers to herbicides that prevent seeds from sprouting, while enhancement of root growth does not relate to herbicide function but rather to fertilizers or plant growth regulators.