Before applying broadleaf weed control to newly seeded grass, you must wait until the newly sprouted grass has been mowed three times or wait at least 30 days, whichever time frame is longer.
If applied too soon after grass germination, broadleaf weed control will kill or weaken young seedlings.
Remember, the three-mow rule is for new grass only, not for seeding into an established lawn. The rate of growth for established lawns is different than that of seedlings.
Before applying any herbicide, carefully read and follow label instructions.