WSU Extension

Hortsense

Weeds : Annual bluegrass : Poa annua
(revision date: 4/7/2021)

Family: Poaceae (Graminae)
Cycle: Annual/Perennial
Plant Type: Grass
Use Integrated Pest Management (IPM) for successful weed management.

Biology
Annual bluegrass leaves are folded in the bud and have a distinct midvein. The leaves are about 1/8 inch wide and cupped at the tip like the prow of a canoe. The ligule, occurring at the point where the leaf blade joins the leaf sheath, is small, membranous, and slightly pointed. Auricles are absent. Leaves and stems are smooth. The seeds are borne in a loose, open panicle (a branching seed head roughly triangular in outline). Overall, the plant is light green, with spreading to erect flattened stems growing two to twelve inches long. Annual bluegrass often forms dense clumps. The main vegetative growth period is in fall and winter, with flowering and seed production occurring from March to August. Annual bluegrass often goes dormant in hot weather, resulting in unattractive brown patches in lawns. The common name is somewhat misleading, as there are both annual and perennial varieties of annual bluegrass.
Habitat
Annual bluegrass thrives in lawns, gardens, cultivated crops, roadsides, and other open spaces. It can be especially damaging in lawns, where it grows somewhat faster than other grasses and dies once it reaches maturity, resulting in undesirable brown spots in the lawn. It is commonly discovered as an impurity of lawn grass seed.

Management Options

Non-Chemical Management
  • Maintaining a healthy planting or turf area to provide competition will prevent weed establishment.
  • Cultivation (rototilling or hoeing) will effectively eliminate plants.
  • Hand-pull to eliminate weeds.
  • Careful digging is useful to manage weed populations. However, digging can carry undesirable weed seed to the surface and foster further germination.
Select non-chemical management options as your first choice!

Chemical Management
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

Read the label for application timing of the products listed. Preemergent herbicides can be used to help limit annual bluegrass. These are more effective in eastern Washington. In western Washington, some of the more effective pesticides should be applied by a licensed professional. Glyphosate products should be applied as spot treatments only! NOTE: Some ingredients listed here are only available in combination. Read the label carefully on combination products to make sure the product is suitable for your specific situation.

Landscape areas
  • glyphosate
  • dichlobenil
  • oryzalin
  • products containing benefin
  • trifluralin
  • products containing diquat
  • pendimethalin
Turf areas
  • products containing benefin
  • pendimethalin
  • benefin, trifluralin
Bare ground areas
  • glyphosate
  • dichlobenil
  • products containing diquat
Images
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Caption: Annual bluegrass
Photo by: T. Miller
Caption: Annual bluegrass flowers
Photo by: T. Miller
Caption: Annual bluegrass boat-shaped tip
Photo by: R. Parker
Caption: Annual bluegrass ligule
Photo by: B.M. Johnson
Caption: Annual bluegrass seed head
Photo by: R. Parker
Caption: Annual bluegrass
Photo by: T. Miller
Caption: Annual bluegrass
Photo by: T. Miller