Old turf areas eventually are invaded and often dominated by naturalized grasses including bentgrasses, roughstalk bluegrass, annual bluegrass, velvetgrass, tall fescue, quackgrass, and bermudagrass. Managers who desire pure turf stands need to renovate periodically by killing all vegetation and reseeding.
Most attempts at chemical renovation fail outright or provide only short-term control of weedy grasses. For good results, managers must completely kill weeds and prevent re-infestation from seed. To optimize kill of weedy grasses, leave the target turf un-mowed for several weeks as it grows vigorously. In spring, the best time to spray cool-season grasses is at early flowering, to maximize kill of difficult grasses such as velvetgrass, bentgrass, and tall fescue. In fall, spray turf when new growth is at least 3 inches tall. Summer sprays often are ineffective due to poor translocation to crowns and rhizomes. Remember, good foliar kill does not always mean complete plant kill.
On renovation sites replanted with straight perennial ryegrass, a selective preemergence herbicide containing ethofumesate can be applied to control germinating annual bluegrass. Applied properly, ethofumesate gives 90% to 100% control of germinating annual bluegrass with no harmful effects on the developing ryegrass turf.