What type of herbicide is applied after weeds have already appeared?

The correct choice is postemergence herbicide, which is specifically designed to be applied after weeds have emerged from the soil. This type of herbicide works by targeting the weeds that are actively growing and visible, allowing for more effective control of established weed populations.

Postemergence herbicides can be selective, affecting only certain types of plants while leaving desired crops or turf unharmed, or non-selective, which kill all green plant material they come into contact with. The timing of application is crucial, as these herbicides need to be used when the weeds are still young and actively growing to ensure optimal absorption and effectiveness.

In contrast, preemergence herbicides are used before weed seeds germinate, preventing them from growing at all. Selective herbicides target specific weed types while minimizing damage to other plants, and non-selective herbicides indiscriminately eliminate all vegetation. Understanding the timing and target audience of each herbicide type is key to successful weed management in turf systems.