Are you 100% sure you have annual bluegrass? Or could it be rough bluegrass? Annual bluegrass is a common winter annual weed that is very difficult to control as there are limited herbicides that can be POST applied in cool season grasses. Rough bluegrass is very similar to annual bluegrass but it is a perennial weed that reproduces from vegetative tissues instead of seeds. Therefore, our PRE applications will decrease annual bluegrass populations but not rough bluegrass populations.
See photos here