How do most foliar-applied herbicides move primarily in the plant?

Herbicides that are applied to the foliage of plants primarily move through the phloem. The phloem is responsible for transporting the products of photosynthesis, primarily sugars, from the leaves to the rest of the plant. When herbicides are absorbed through the leaves, they often navigate through the phloem to reach various growing tissues. This is particularly important for systemic herbicides, which are designed to kill the plant by moving throughout its tissues and disrupting physiological processes such as growth and metabolism.

The roots play a key role in nutrient and water uptake but are not the primary pathway for foliar-applied herbicides, as those herbicides are intended to be absorbed via the leaf surface. The xylem is involved in transporting water and soluble minerals from the roots to the leaves, not in distributing the compounds absorbed through foliar applications. Finally, the cuticle serves as a protective barrier on the leaf surface that can affect herbicide absorption, but it is not a method of movement within the plant.