Poa annua, or Annual Bluegrass, is a common winter annual grassy weed found in Oklahoma lawns at this time of year. It mainly germinates in the fall with the first cool rains, and stays fairly small until the following spring. It’s a lighter green color and shallow-rooted compared to the existing turf. It is a prolific seeder, producing hundreds of tiny seeds, which will lead to the next generation of weeds if left un-checked.
The best way to control Poa annua is with the application of a pre-emergent herbicide in the fall, before weed seeds germinate. At LawnAmerica, we use a great new product named Specticle in bermudagrass and zoysiagrass, which does an excellent job of prevention. Later in the fall, we add an additional product names Simazine, which will also control any newly emerged weed plants. In fescue turf however, we cannot apply these fall pre-emergent products, since they would inhibit fescue from germinating in the fall, and they are not even labelled for use in fescue turf. There is one product named Prograss that can be applied in late fall and winter to a fescue lawn and control Poa annua. It’s an expensive treatment, and usually not recommended. We feel that in a thick, healthy fescue turf, the Annual Bluegrass is not that evident in the turf, and does not justify treatments in most cases.
If Poa annua is present now during April and May, it can be spot treated with various post-emergent products such as Monument, Revolver, and Certainty. These will take out the bluegrass without harming the desirable turf. However, as the bermudagrass greens up and the weather turns hotter, this tends to choke out any Poa annua weeds. In wet, shady areas of the lawn, Annual Bluegrass can remain all year as a perennial weed in some areas.