Roughstock Bluegrass (Poa trivialis) – Control
Q: A couple of weeks ago, our fescue lawn was diagnosed with having an invasive winter grass called Poa trivialis. The grass has consumed over 60% of my lawn. What would you do?
A: You are not going to like my answer.
Poa trivialis, roughstock bluegrass, and Poa annua, annual bluegrass, are both cool season grasses.
Both die out or go dormant during summer heat.
Poa trivialis is much harder to control because it is perennial.
There is some current research on new herbicides that can suppress roughstock bluegrass but there’s nothing selective enough that will kill it and not your lawn grass.
So killing everything with glyphosate (click for sources) and reseeding is sometimes the only option.
It’s hard to tell you what to do now in late spring. You could kill everything and then reseed with fescue but the fescue won’t survive July heat without strict attention to watering.
Or you could simply mow the bluegrass until fall, pray for a mild summer that doesn’t cause it to go dormant, then kill the existing bluegrass in September and reseed the fescue then.