Problem grass weeds in cool season turf often cannot be controlled except by complete renovation. The following is an article on the subject.
Assessing Turf for Complete Renovation.
Mid-summer is the time to assess turf areas for the need to do a complete renovation. In particular, where problem perennial grasses such as wiregrass, nimblewill, zoysiagrass, bentgrass, orchardgrass, or coarse type tall fescues have become established in desired cool season turf, a complete renovation needs to start in summer with herbicide applications to kill them. Other reasons for a complete renovation include heavy traffic, disease pressure, insect damage, or general loss of stand due to other stresses.
If you have heavy infestations of problem perennial grasses, one option is to apply 2 applications of glyphosate herbicide, three weeks apart. You need to allow sufficient time for any remaining weeds to die after the second application before seeding in late summer; therefore, the first application should go on in late July through early August. For heavy infestations of Zoysiagrass or wiregrass, 3 applications may be needed starting in mid-July. For orchardgrass, bentgrass, coarse tall fescue, or other undesired cool season perennial grasses, turf areas should be irrigated to encourage growth prior to applying glyphosate as it will not work on drought stressed or heat dormant plants. For troublesome perennial weed patches, Basamid soil fumigant may be another option. Basamid is applied as a granule and is watered in. It performs best if it is tilled in or is tarped with plastic. Research has shown good control of nimblewill, bermudagrass, and creeping bentgrass by fumigation with Basamid.
Gordon Johnson, Extension Horticulture Agent, UD, Kent County