In many fescue lawns, overseeding is necessary every year or two. Fescue tends to thin out on hard, clay soil and summer heat and drought are no friends to this grass. Bermudagrass is a common weed that can creep into fescue turf and cause an unsightly patch of brown in an otherwise green lawn in the winter. Early August is the time to kill bermudagrass if you intend to plant fescue seed in September.
Bermudagrass is a tough adversary. It travels both under- and above-ground. It stores plenty of energy to resprout after being damaged. For these reasons, it is important to kill bermudagrass completely in a fescue lawn.
The best weed killer to use is glyphosate (Roundup). Spray the bermudagrass patch and wait two weeks. Spray again. In early September, examine the dead patch. You may be surprised to see sprigs of bermudagrass coming up from the soil! It is time then to spray once again to finish off the opponent.
Just seven days later, fescue seed can be planted at the optimum time.