Which type of herbicide remains active for long periods in soil or water?

The type of herbicide that remains active for long periods in soil or water is best classified as a residual herbicide. Residual herbicides are designed to persist in the environment, providing prolonged weed control by remaining active in the soil or water after application. This characteristic allows them to inhibit weed germination and growth over extended periods, making them effective for long-term management of unwanted vegetation. They often have specific chemical properties that enable their persistence and effectiveness in a range of environmental conditions.

In contrast, other types of herbicides serve different purposes and exhibit different behaviors in the environment. Nonselective herbicides kill all plant types they contact, making them useful for general weed control but not necessarily designed to remain active for extended periods. Contact herbicides are effective only at the point of contact with plant tissues and do not provide lasting effects. Translocated herbicides move within the plant after application, targeting the root system but do not focus on soil or water persistence. Understanding these distinctions helps in selecting the appropriate herbicide for specific weed management scenarios.