Annual bluegrass — a serious spring weed problem in Virginia’s lawns.
Annual bluegrass puts on a showy display of its seedheads every spring just before it dies in our summer heat. What can be done now and in the future to better manage this important lawn pest?
Numerous questions have come into the Virginia Tech Turf Team’s offices in mid-April regarding chemical alternatives to control annual bluegrass (scientific name of Poa annua, often referred to as Poa or Poanna) in homelawns in the spring. You will recognize this plant by its light green color compared to most other turfgrasses, but more specifically by its prolific seedhead formation in mid-spring. Unfortunately, there is really nothing that can be done now other than to mow the turf to reduce seedhead numbers and improve turf uniformity. Most Poa behaves as a true winter annual plant; that is, it germinates in the fall, produces seed in the spring, and dies. Hence, the plant is nearing death very soon, so any attempts at chemical control are pretty much pointless at this time. Poa is an annual problem because of the prolific number of seed that it produces, so you will never eradicate it from your lawn and landscape—you will only be able to manage it.
Though it is not of any help with the weedy mess you might have in your yard now, the best bet to reduce Poa populations for next spring is to plan on making a fall preemergent herbicide application in the first couple of weeks of September. Why not make a note of this on your calendars now so you won’t forget? This control strategy works well on both Poa and a whole host of other winter annual broadleaf weeds (for example chickweed, deadnettle, henbit, geraniums, etc.) IF you DO NOT plan on seeding any desirable turfgrasses next fall. The herbicides available for homelawn use do not differentiate between weed or turf seeds. If you must reseed a cool-season turf, then do everything you can to enhance turf establishment such that the new grass overwhelms the Poa simply due to the competition. Your keys to success in establishment are things such as proper testing and preparation of the soil, appropriate seeding rates, optimal seeding timing, and irrigation management. For those of you growing warm-season turfgrasses, you have the additional option of treating winter weeds with a non-selective herbicide such as glyphosate when the turf is fully dormant, an option not available in cool-season turfgrass stands.
More specific information on turf management is available through the VT Turf and VT Turf Weeds links on this webpage. You can find a wide array of horticulture-related topics through the Virginia Cooperative Extension webpage at http://www.ext.vt.edu. This site contains links to all VCE publications and contact information specific to your locale. Please contact your local Virginia Cooperative Extension office if you require further assistance.