What herbicide kills Johnson grass?
Will 2,4-D kill Johnson grass?
If it truly is Johnson grass it is a perennial so a pre-emergent herbicide won't work. Since we lost MSMA as a herbicide, weed grasses are tougher to eradicate, but there are a few options for use during the growing season. Quinclorac is now used and is often mixed with 2,4-D as a broadleaf weed and grass killer.