Annual bluegrass is one of those weeds that you just love to hate. Its clumps pop up during the winter in the home lawn and continue to grow green while the rest of your lawn stays completely dormant. You spray it with a general herbicide and nothing happens. You mow it down repeatedly, but it grows so low it just comes back and continues to produce those little white seedheads. Nothing works. You can’t kill it.
When spring finally arrives, it starts to die leaving yellow patches, and making the lawn look less than perfect. Luckily though, annual bluegrass goes away and isn’t a problem during the summer. Or does it???
Being an annual weed, annual bluegrass, or poa annua, produces seeds in early spring so that it will be back again next year. Those seeds fall off in the yard and remain nestled in the soil and amongst the nice green centipedegrass, zoysiagrass, and bermudagrass lawns until around August. Yes, I said August because that is when the annual bluegrass seeds start to germinate. In the fall, you cannot see the new sprouts of annual bluegrass because most our lawns are still green and growing up until mid November. By November, it is way too late to do anything. The beast called annual bluegrass has taken root and is ready to become center stage.
However, knowing that annual bluegrass germinates in August and early September, that is the critical time to take action toward controlling it. Before the seeds fully germinate and take root, apply a preemergence herbicide to your lawn. Products recommended for controlling crabgrass will also control annual bluegrass: Scott’s Halts Crabgrass Preventer (pendimethalin), Green Light Crabgrass Preventer (benefin and trifluralin), Sta-green Crab-ex Crabgrass Preventer (dithiopyr), Spectracide Weed Stop Crabgrass Preventer (dithiopyr), Vigoro Crabgrass Preventer (dithiopyr) and Prodiamine. Atrazine is also recommended but note that it cannot be used on bermudagrass lawns while the grass is still green and actively growing.
Source: Shane Harris, Regional Extension Agent
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