Which of the following herbicides is a contact herbicide?
Show Hint
Diphenyl ether herbicides like oxyfluorfen are contact, light-dependent (photodynamic) herbicides.
They work by inhibiting the protoporphyrinogen oxidase (PPO) enzyme, leading to rapid membrane lipid peroxidation upon light exposure.
Step 1: Understanding the Concept:
Herbicides are classified as systemic (translocated within the plant) or contact (causing injury only to tissues they physically touch).
Contact herbicides require thorough spray coverage to achieve effective weed control. Step 3: Detailed Explanation:
- Atrazine (A) and Pyrazon (B): These are systemic herbicides that are absorbed by roots and translocated to other plant parts.
- Oxyfluorfen (D): This is a diphenyl ether herbicide that acts primarily as a selective contact herbicide. It requires light to produce reactive oxygen species that disrupt cell membranes, leading to rapid cell death and desiccation of contacted foliage.
- Nitrofen (C): Although also a diphenyl ether, it has been banned globally for many years, and oxyfluorfen remains the classic representative contact herbicide of this class in modern agronomy. Step 4: Final Answer:
The contact herbicide is Oxyfluorfen, which corresponds to option (D).
