Poa Annua, or Annual bluegrass, is an annual weed that looks similar to a regular lawn grass for a short while. It has shallow roots, and develops a short seed head early in the season. By the time summer heat hits, the weed dies off, leaving big brown areas in the lawn.
Poa Annua, or Annual Bluegrass
Poa annua is as common a lawn weed as they come. It looks a little like Kentucky bluegrass, except it has a lighter shade of green, shallower roots, and less drought resistance. It dies off when the weather gets hot, leaving big empty patches in your lawn. Keep it out by spreading a crabgrass preventer in late summer, before seeds can sprout in the fall.
Poa annua loves damp, shady areas. Fight the weed by watering deeply and infrequently. Its shallow roots can't reach down to where the moisture is.
Set Your Mower High
Poa annua is short. When you mow your grass at high, between 3-4 inches, you make it hard for annual bluegrass to survive. Lawns with taller grass tend to have very few Poa annua problems.
Use a Pre-Emergent in Late Summer
The Poa annua seed heads that were dropped in the spring are waiting for fall to sprout. You can stop them by spreading a pre-emergent in August or early September. That will stop seeds from sprouting.