What is the difference between contact and systemic herbicides?

What is the difference between contact and systemic herbicides?

• A. Contact herbicides are absorbed by and move within the plant.
• B. Contact herbicides affect only treated areas.
• C. Systemic herbicides affect only leaves.
• D. Systemic herbicides move only in the soil.

Answer: (B)

The main idea is how the herbicide travels after you apply it. Contact herbicides affect only the plant tissue they actually touch and do not move inside the plant, so only the sprayed areas are damaged. Systemic herbicides are absorbed and transported through the plant (via the xylem or phloem) to other tissues, including growing points, roots, or untreated parts, which is why they can kill more than just the sprayed spot. This is why the statement that contact herbicides affect only treated areas is the best description. The other options mix up where movement occurs or what is moved: movement within the plant is characteristic of systemic action, not contact; systemic isn’t limited to leaves; and systemic movement isn’t restricted to soil movement.

The main idea is how the herbicide travels after you apply it. Contact herbicides affect only the plant tissue they actually touch and do not move inside the plant, so only the sprayed areas are damaged. Systemic herbicides are absorbed and transported through the plant (via the xylem or phloem) to other tissues, including growing points, roots, or untreated parts, which is why they can kill more than just the sprayed spot. This is why the statement that contact herbicides affect only treated areas is the best description. The other options mix up where movement occurs or what is moved: movement within the plant is characteristic of systemic action, not contact; systemic isn’t limited to leaves; and systemic movement isn’t restricted to soil movement.