Grass is one of the strangest plants we grow. Technically, grass is a weed.
Certain species have become cherished groundcovers, while others are an eyesore. One of the most frustrating among these unwanted grasses is Poa annua.
Some common names are:
- Annual bluegrass
- Annual meadow grass
- Poa
What makes this species so frustrating is that it’s an annual that’s quick to seed- even if you cut the stalks.
How To Get Rid Of Poa Annua
It’s impossible to rid your lawn or garden of this grass completely.
But you can keep it under control with a multi-step program.
Of course, first, confirm your invader is Poa annua.
Selective herbicides (and even many non-selective) might not work if you make a misdiagnosis.
Identifying Annual Bluegrass
Several types of grass can be pesky visitors to your lawn or garden.
Not all areas are distinguishable as crabgrass.
For example, annual bluegrass resembles creeping bentgrass.
Thus, it is important to get identification before treating your lawn.
Annual bluegrass most often germinates in the fall or sometimes in early spring.
At first, the bright green leaf blades may appear as healthy new turf.
However, the difference becomes more visible as it grows.
The leaves are short with a blunt, boat-shaped tip and appear soft and smooth with a drooping nature and fine serration along the edges.
The stems are 6″ to 10″ inches tall with 2″ to 3″ inch triangular panicles.
It only takes 6 weeks to flower, and it dies shortly afterward.
This short lifespan is offset because annual bluegrass can drop ripened seeds 8 months out of the year.
However, it can remain in flower all year in warmer climates.
Also, annual bluegrass seeds can remain dormant in the soil for several years before germinating. Hence, it’s almost impossible to get rid of it once it’s in your yard.
Fun fact: Poa annua and Agrostis stolonifera (creeping bentgrass are both parts of putting greens on golf courses.
Sizing Up The Situation
Have a look around your property to assess where annual bluegrass will most likely appear.
Then, you will see where to focus your treatments, including:
- Shaded areas
- Moist or compact soil conditions
By cutting the grass down to 1″ inch, it’s often easier to spot patches of Poa annua.
Take note that this plant has a clumping habit, often making it more visible among shorter grass.
Using A Pre-Emergent
Pre-emergent herbicides work by targeting the seeds of weeds and plants before they can germinate.
As a result, you have to be careful not to use them while spreading new turf seeds.
Annual bluegrass often germinates in late summer, after your desired grasses have grown and established themselves.
Of course, pre-emergent herbicides are most often used in early spring.
They will last as long as 4 to 6 months (depending on the product).
Here are the steps to follow when using pre-emergent herbicides:
- Check the label of your pre-emergent to ensure the herbicide is compatible with your lawn’s grass type and effective against Poa Annua.
- Remember, the weed’s seeds activate in cooler weather.
- Apply the pre-emergent herbicide when temperatures drop below 70° degrees Fahrenheit for more than two days in a row.
- Apply before the first frost.
- Apply a second treatment 6 to 8 weeks after the first to ensure the most effective coverage.
This application can help reduce missed spots and extend the herbicide’s effective lifespan.
Remember, pre-emergent herbicides only work on germinating seeds.
Use a post-emergent formula to tackle existing annual bluegrass.
Using A Post-Emergent
Attacking germinating seeds won’t prevent established grass from seeding.
Even mowing off the stalk won’t stop this.
Post-emergent herbicides are a great tool in your arsenal to deal with existing bluegrass.
As with pre-emergent formulas, post-emergent herbicides may be either selective or non-selective.
Always check the label to ensure a product will do what you need it to do for your particular lawn.
It generally takes 2 to 4 weeks for the herbicide to do its job.
Both contact and systemic formulas will kill down to the roots but are ineffective against seeds.
Spot Treatments
Finally, spot treatments are a great way to help keep your lawn looking good and reduce an annual bluegrass outbreak at the same time.
Use a non-selective, post-emergent herbicide such as Roundup once you verify it’s compatible with your lawn.
When temperatures go above 86° degrees Fahrenheit, bluegrass will turn brown and die.
It is ideal for working your way through the lawn during this time, digging up these weeds by their roots.
This is an excellent way to avoid using chemicals but won’t protect your lawn from any existing seed.
Poa annua has a much easier time claiming barren land than competing with a well-established lawn.
By keeping your lawn thick, healthy, and well-roomed, you can keep weed outbreaks to a minimum.