Agronomy and Horticulture, Department of


Foliar Absorption and Phloem Translocation

Document Type

Learning Object

Date of this Version



Plant and Soil Sciences eLibrary (PASSeL) Lesson


Copyright © 2019 Scott J. Nissen, Tracy M. Sterling, and Deana Namuth. Used by permission.

This project was supported in part by the National Research Initiative Competitive Grants CAP project 2011-68002-30029 from the USDA National Institute of Food and Agriculture, administered by the University of California-Davis and by the National Science Foundation (NSF), Division of Undergraduate Education, National SMETE Digital Library Program, Award #0938034, administered by the University of Nebraska. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the USDA or NSF.



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. Absorption and translocation of xylem mobile herbicides will be 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.