How do translocated herbicides effectively control weeds regrowing from underground parts?

Translocated herbicides are designed to move throughout the plant after being applied, allowing them to reach various internal structures, including the underground parts that are responsible for regeneration, such as roots and rhizomes. When these herbicides are absorbed, they travel from the site of application (often the foliage) to other areas of the plant, including those underground parts. This movement is critical for effectively controlling perennial weeds that have dormant structures below the soil surface, as it ensures that the herbicide can kill not only the visible parts of the plant but also the regenerative parts that could lead to regrowth.

In contrast, the other choices do not accurately represent the mechanism of translocated herbicides. Focusing only on the foliage would mean the herbicide would not reach the roots, which is essential for controlling persistent weeds that regrow from underground tissues. The requirement for direct contact with soil or that they are only sprayed on the soil surface would not allow the herbicidal action to affect the parts of the plant that regenerate, thus leading to inadequate control.