Root Absorption and Xylem Translocation Overview and Objectives

Plant roots and below ground shoots have few barriers to herbicide absorption; however, interactions with soil particles and soil organic matter have significant impacts on the amount of herbicide available for plant absorption. Plant roots and below ground shoots (hypocotyls or coleoptiles) are lipophilic by nature and do not have thick, waxy cuticles like leaves. Lipophilic and hydrophilic herbicides reach the root surface by bulk transport in soil water; however, there are a few examples of herbicides that reach the root as a vapor. Soil-applied herbicides can translocate to the shoot or remain in the root system. Soil-applied herbicides that translocate to the shoot in the xylem tend to accumulate in mature leaves that transpire the most water. The herbicide’s lipophilic/hydrophilic nature will determine if the herbicide translocates to the shoot. Foliar absorption and translocation of phloem-mobile herbicides will be discussed in a separate lesson. 

At the completion of this lesson, learners will aquire the information necessary to understand the following:

1. How clay content, organic matter and soil pH influence herbicide availability
2. How herbicides move to the root and how chemical characteristics of the herbicide can be used to predict root absorption
3. How chemical characteristics influence herbicide translocation to the shoot
4. Pathways and barriers to herbicide movement from root to shoot