Which herbicide is used before weeds germinate?

The correct choice is a preemergence herbicide because its primary function is to prevent weed seeds from germinating and establishing themselves in the soil. These herbicides create a chemical barrier in the soil during the period before weeds emerge, effectively inhibiting the growth of various weed species at their initial stage. This proactive approach is crucial in turf and ornamental management, as it reduces competition from weeds and allows desirable plants to thrive without the stress of weed competition.

In contrast, postemergence herbicides are applied after weeds have already germinated and become established. They are typically used to manage existing weed problems rather than prevent them. Systemic herbicides work by being absorbed and transported throughout the plant, affecting the entire weed but they are also applied after the weeds have emerged. Contact herbicides kill the parts of the plants they come into direct contact with, but can also only be applied when weeds are visible and actively growing.

Thus, preemergence herbicides are essential for integrated weed management strategies, allowing for the suppression of weeds before they have a chance to compete with turf and other plants.