No. It doesn't kill weeds ot grass. It only prevents them from germinating from seed.

Can you use preen on grass?

Preen Lawn Weed Control kills 200 weeds and is the perfect choice for taming an especially weedy lawn. This product eliminates lawn weeds such as dandelions, chickweed, clover, and thistle by killing the root! ... Prevents crabgrass and other common grassy weeds. Apply later in spring for season-long control.

Does preen stop grass from growing?

Using Pre-Emergent Weed Killer

Thus, they are of limited effect as a measure to prevent perennial grasses from growing in your garden. Pre-emergents can be used along with other measures to help control grasses and weeds, but they will also prevent desirable seeds from germinating.