Are soil-applied herbicides only translocated in the photosynthetic stream (phloem)?

• A. True
• B. False
• C. Depends on the herbicide type
• D. Only in certain plants

Answer: (B)

Soil-applied herbicides are not solely translocated through the phloem, which is responsible for transporting photosynthates (like sugars) from the leaves to other parts of the plant. Many herbicides can move through both the xylem and phloem systems. The xylem primarily transports water and dissolved nutrients from the roots to the leaves, where they are needed for various metabolic processes. Since many herbicides are taken up by the roots and can translocate through the xylem, they can affect various physiological functions throughout the plant, regardless of whether the plant is actively photosynthesizing.

In addition, the mechanism of translocation can depend on the herbicide's chemical properties, making it possible for different types to move through different plant tissues depending on their mode of action. Thus, the classification of soil-applied herbicides as only moving through the phloem is inaccurate, supporting the assertion that the answer is false.