What distinguishes preemergence herbicides from postemergence herbicides?

Preemergence herbicides are specifically designed to prevent the germination and growth of weeds before they emerge from the soil. They create a chemical barrier in the soil that inhibits seed germination, making them effective in controlling weed populations by stopping them before they can take root. This is particularly useful for managing annual weeds, as it targets their life cycle before they even begin to grow.

On the other hand, postemergence herbicides are intended for use on weeds that have already emerged. These herbicides work by being absorbed through the foliage of existing weeds to disrupt their growth processes, ultimately leading to their death. Unlike preemergence herbicides, postemergence products are not effective unless the weeds are already visible and growing.

The selected answer highlights this key distinction, underscoring that preemergence focuses on prevention prior to germination while postemergence addresses weeds that have already become established.