Poa Annua, affectionately known as annual bluegrass, is the major winter and early spring grassy weed in lawns. It is identified by its light green color, boat-shaped leaf tip, and crinkled leaf (due to stretch marks) in the spring. How you control Poa annua depends on how you left your lawn in the fall. Did you overseed your bermudagrass, or not?
NON OVERSEEDED TURF: BERMUDA ALLOWED TO GO DORMANT
In this case, your best bet for eliminating Poa annua is to apply a pre-emergence weed control agent to the lawn in mid-September. This will prevent the Poa from emerging! The Poa that comes up after this (or any existing Poa, for that matter), can be treated post-January with ROUND-UP or FINALE. Spot spray the Poa (and any other winter weeds) with either product. Make sure the bermudagrass is fully dormant (straw-colored, if you are using ROUND-UP). If the lawn is 10% green or more, it may be safer to use FINALE as directed spray. FINALE will not translocate to the rhizomes of bermudagrass as ROUND-UP will. The weeds must not be dry when you apply either of these products. Do not irrigate until two days after spraying. In 7-10 days, the Poa will be dead.
As a lawn owner, you have no real effective options for using a selective herbicide to remove Poa annua from a ryegrass (overseeded) lawn.
Your best bet is to do the following:
‚ Raise the mowing height. Poa annua is less competitive at high mowing heights, and will be somewhat crowded out by the shade of the taller ryegrass. Mow at 2.5 inches when the grass reaches 3 1/4 to 3 2 inches, at the highest.
‚ Bag the clippings. Let the lawnmower catch the grass clippings. This will remove the seed heads to some extent. Do this throughout the flowering period of Poa annua. The seeds will die in the compost.
‚ Adjust your watering schedule carefully to keep the lawn on the dry side. Poa annua does not like dry soil. If you irrigate the lawn right before it wilts, or foot tracks, the Poa will be more stressed than the ryegrass, and thus less competitive.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.