What is the name of a compound that can move freely within a plant after application?

The term that describes a compound that can move freely within a plant after application is systemic. Systemic herbicides are designed to be absorbed by the plant and then translocated throughout its tissues, allowing them to affect areas beyond where the herbicide was applied. This movement within the plant enables the compound to target root systems and other growth points, making it especially effective against perennial weeds or plants with extensive root structures.

In contrast, contact herbicides affect only the parts of the plant that come into direct contact with the chemical and do not move within the plant. This limits their efficacy, particularly with larger or more established weeds. Residual refers to the duration a compound remains active in the environment or soil, and foliar pertains to applications made directly to the leaves. Neither of these terms captures the ability of a herbicide to move within the plant, making systemic the correct choice.