Poa annua is a type of bluegrass that is considered an invasive weed species in many turf grasses. It is problematic for a bevy of reasons. The color of the blade is lighter than many other turf grasses making it difficult to blend in. It cannot perform well in summer heat causing die-back, thinning or patchiness. It also throws up tall seed heads in the late spring and early summer. Once the weed is established, it is difficult to eradicate entirely or quickly as ungerminated seeds survive in the soil for up to three years.
Mow your Poa-infected lawn weekly during the late spring and early summer when the seed heads are developing in profusion. Always use a catcher on your lawn mower to prevent the redistribution of seeds onto the thatch where they will germinate and start the plant process anew.
Spray a pre-emergent herbicide product on your Poa in early September before the seeds have a chance to germinate. Make a second application in the spring to catch the seeds as they are germinating. Repeat this treatment process every year until the problem is under control or eliminated. Apply the spray product according to the label directions being sure to wear a face mask to prevent accidental inhalation of the mist or vapors.
Apply a post-emergent herbicide product containing the active ingredient ethofumesate two to three times from September to December each year at four-week intervals. This product must be administered by a lawn care professional and is not sold retail. The limiting effect on the Poa can be seen in the fall after a treatment cycle but will improve even more the spring after treatment begins.