Foliar Absorption and Phloem Translocation Overview and Objectives

Herbicides must be absorbed into plants in order to be effective. Herbicide absorption can occur through leaves, roots or both. The process by which herbicides kill weeds, called mode of action, requires herbicide absorption and may also require herbicide movement or translocation within the plant. Translocation means that the herbicide moves from the site of absorption to some other plant part. Foliar-applied herbicides that have the necessary characteristics to move in the phloem will translocate to areas of the plant that are actively growing; however, not all foliar-applied herbicides move from the leaves that intercepted the spray solution. Herbicides that are absorbed but not translocated are called contact herbicides, while herbicides that translocate to shoot or root meristems are called systemic herbicides. This lesson is divided into two major sections; absorption and translocation.  Root absorption and translocation of xylem-mobile herbicides is discussed in another lesson. 

At the completion of this lesson, learners will have acquired the information necessary to describe the following:

1. Major barriers to foliar absorption of herbicides.
2. Basic pathways of herbicide movement in plants following foliar absorption.
3. Environmental conditions that can influence herbicide absorption and performance.
4. Adjuvants and their role in herbicide performance
5. Herbicide characteristics that affect foliar absorption and translocation.