What characteristic distinguishes residual herbicides from others?

Residual herbicides are characterized by their ability to provide long-term weed control. This is primarily due to their formulation, which allows them to remain active in the soil for an extended period. After application, these herbicides can persist in the environment, continuing to target and inhibit the growth of weeds over time, often for weeks or even months. This long-lasting effect makes them particularly useful in managing weed populations effectively, especially in situations where continuous control is necessary.

The other options, while they may pertain to different types of herbicides or pesticides, do not capture the essence of what defines residual herbicides. For instance, many herbicides can decompose quickly or may have a delayed action in plants, but this doesn't specifically define residual herbicides. Additionally, effectiveness against insects pertains to insecticides rather than herbicides, which focus on plant pests.