Poa annua, also known as annual bluegrass, is an invasive weed native to Europe. Distribution to other areas on the globe has allowed Poa annua to become one of the most common species of weed found in California, according to the University of California Integrated Pest Management Program. Poa annua poses a particular threat to golf courses and fairways where solid turf is paramount to successful course management. Killing hardy Poa annua requires a dedicated weed management program.
Apply a pre-emergent herbicide containing Bensulide, oxadiazon and dithiopyr to areas that are affected by Poa annua. Application should be made in the late summer in northern climates and early fall in southern habitats, as Poa annua is a cool-season germinator.
Repeat the application of pre-emergent herbicide 45 to 60 days after the initial application. According to Grounds Maintenance, an industry publication for golf and green professionals, pre-emergent herbicides provide 90 to 95 per cent effectiveness in killing Poa annua prior to germination.
Mow your turf with a lightweight lawnmower and aerate frequently to prevent formation of the compacted and wet soils that favour Poa annua growth.
Use a bagger attachment when mowing the turf to collect clippings, preventing the spread of seed. Further prevention can be achieved by thoroughly rinsing the mower blades after mowing the turf.
Over-seed affected areas with the desired turf, such as bent grass, in late summer or early fall, prior to the emergence of Poa annua. Over-seeding provides a competitive growth area and gives bent grass a chance to choke out Poa annua infestations before they germinate.
Apply a nonselective herbicide containing glyophosate during active growth periods in spring and early summer. Glyphosate should be used only as a spot treatment, and treated areas will require reseeding of the desired turf grass.
Wear gloves when applying herbicides to protect skin from chemical irritation.