When are preemergence herbicides typically applied?

Preemergence herbicides are applied before the emergence of weeds, which is why this choice is the correct answer. These herbicides work by creating a chemical barrier in the soil that inhibits the seeds of certain weeds from germinating. Timing is critical; they need to be applied before the weeds begin to sprout, providing an effective means of weed prevention without impacting already established plants or grass.

Applying them after seeds have germinated would not be effective, as the herbicides target the physiological processes of germinating seeds and emerging seedlings. Similarly, applying them when grass is actively growing may risk damaging the turf and detracting from its health and vigor. Finally, while winter months might be a time with fewer weed pressures, they are not the optimal time for application since these products are designed to prevent spring and summer weed growth. Thus, for effective weed management, preemergence herbicides must be utilized before weeds appear.