2,4-D not effective on which plant type?

• A. Grasses
• B. Broadleaf plants
• C. Aquatic macrophytes
• D. Algae

Answer: (A)

2,4-D works by mimicking natural growth hormones (auxins) and disrupts growth in broadleaf plants, causing rapid, uncontrolled tissue development that leads to the plant’s demise. Grasses are monocots with different growth regulation and anatomy, which makes them much less sensitive to this mode of action. Because of that difference, 2,4-D does not effectively kill grasses, so the best choice is grasses. (Algae aren’t vascular plants, and aquatic macrophytes that are broadleaf can be affected, but the specific plant type not affected by 2,4-D’s action is grasses.)