In herbicide terminology, what does it mean for a herbicide to be systemic?

A systemic herbicide is one that is absorbed by the plant and then transported throughout its tissues, including the leaves, stems, and roots. This allows the herbicide to affect the entire plant, making it effective against both aboveground and belowground parts. The mode of action is crucial for controlling perennial weeds and certain annual species because merely affecting the area that the herbicide touches (as would occur with a non-systemic herbicide) may not eliminate the plant entirely. Systemic herbicides can disrupt normal plant functions by targeting essential growth processes, leading to the eventual death of the plant. This broad and penetrating ability to impact the entire plant system is what distinguishes systemic herbicides from those that act only locally or specifically target certain plant parts.