True or False: Herbicide group numbers are based on their mode of action.

Herbicide group numbers are indeed based on their mode of action, which is a classification system used to categorize the various herbicides according to how they affect target plants. This system helps in understanding the specific processes that herbicides disrupt in plants, which can include inhibiting photosynthesis, disrupting cell division, or blocking specific enzyme pathways necessary for plant growth.

By grouping herbicides with similar modes of action, it allows for better management strategies, particularly in terms of rotating herbicides to prevent or manage resistance in weed populations. This is crucial for effective weed control and sustainable agricultural practices, ensuring that the same mode of action is not used repeatedly, which could lead to resistance development.

Therefore, the statement that herbicide group numbers are based on their mode of action is true.