What is a contact herbicide?

• A. A herbicide that moves through the vascular system to all plant parts.
• B. A herbicide that damages or kills only portions of the plants it contacts.
• C. A herbicide that kills all plants it contacts.
• D. A herbicide applied to leaves of growing plants.

Answer: (B)

A contact herbicide acts only on the tissue it directly touches. It does not move through the plant’s vascular system, so the injury or kill is limited to the sprayed parts. If you spray a weed’s leaves, only those leaves (and tissues they contact) are damaged, while the rest of the plant, including the roots, may survive and regrow if not contacted.

This is why the description “damages or kills only portions of the plants it contacts” is the best definition. It contrasts with systemic herbicides, which travel inside the plant and kill more parts, even those not directly sprayed. Applying to leaves is a common method, but it doesn’t itself define a herbicide as contact versus systemic; the key idea is the lack of internal movement and localized effect.