Poa Annua Control – How To Get Rid of Annual Bluegrass

Poa Annua Control – How To Get Rid of Annual Bluegrass

Poa annua, or annual bluegrass, is a fast-spreading, grassy weed species that can take over your turf quickly if you don’t get it under control. An infestation of P. annua is very noticeable in a dark green lawn, causing off-color spots, bare patches, and an irregular surface on the lawn. When it comes to weed control, this plant is the bane of many a homeowner’s existence. 

So that begs the question, what is Poa annua, and how do I kill it? This post should help you cool-season turf owners improve your weed control game to get rid of annual bluegrass — and keep it gone.

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What is Poa Annua

A cool-season grassy weed that invades lawns all over the world, Poa annua germinates in late fall — usually in early September, when soil temperatures drop to 70 degrees and below. P. annua lives overwinter in a vegetative state and begins to grow rapidly the following early spring, peaking in June.

As the summer temperatures begin to climb, P. annua, a prolific seed producer, flowers and drops numerous seeds in your lawn before beginning to die off in late summer. But this seed drop guarantees the cycle will begin all over again in late summer or early September, and you’ll be fighting the same weeds come spring. Weed control and prevention is crucial for getting this grassy weed under control in your lawn.

What Does Poa Annua Look Like?

Poa annua grass often grows in clumps. The plant has a lighter shade of lime-green that makes it easy to identify in a darker green, healthy lawn or in turf that’s well maintained. Its white, flowering seed heads make it doubly noticeable in your lawn once it matures. And when the plant begins to die off in late summer or early fall, it leaves ugly bare patches.

P. annua has flat stems, and its leaves are flat, slightly keeled, and have characteristic tramlines. Its characteristic boat-shaped tip is the result of leaves that are abruptly contracted. Transversely wrinkled leaves are a further characteristic of P. annua. The plant grows well in semi-shady areas of the lawn but does best in shady, moist lawns.

This weed grows up to eight inches tall if it isn’t mowed. Its seed heads are one to two centimeters long when flowering, and they’re loosely arranged on spreading branches or delicate paired branches.

Where is Poa Annua Native To?

Poa annua is a cosmopolitan grass found in practically all terrestrial ecosystems, from antarctic regions and temperate areas to relatively undisturbed habitats and urban areas heavily trafficked. It often outcompetes with other plants, from subtropical crops to a healthy lawn in the American suburbs.

This grassy weed has spread well outside its native distribution range, which is primarily the temperate areas of Eurasia. The weed can thrive in a lawn through a dry summer or frozen conditions in almost all areas of the world, and it’s a hardy plant that tolerates trampling and holds up to regular foot traffic.

Image credit: John Gifford

How Does a Grassy Weed Like Poa Annua Grass Spread?

Poa annua, a highly prolific seed producer, spreads its many seeds throughout your lawn in a variety of ways. It’s a weed commonly found in gardens, golf courses, pastures, urban greens, and crop fields at elevations from sea level to around 1,200 feet.

P. annua seeds are often found mixed in with other plant and lawn seed mixes. When these weeds flower, they drop their seeds, and more weeds may come back the next year once the plant germinates again.

Is it Poa Annua or Kentucky Bluegrass?

Both Poa annua and Kentucky bluegrass (KBG) begin to sprout seeds in early spring — usually from May through June — and they’re commonly confused with one another because like the seed of KBG, the P. annua seeds emerge from the top of the plant.

But the most obvious difference between these cool-weather grasses is that P. annua grows out more horizontally, while KBG bunches upwards more vertically. It also has a shallower root system than KGB, which produces more seeds on longer stems. P. annua’s boat-shaped leaf tips also give away its identity.

How To Kill Poa Annua

Some herbicides will selectively kill Poa annua in lawns — but that’s not the only plant they can damage. 

Tenacity Herbicide doesn’t specifically list P. annua on the label, but it will damage the weed grass. Tenacity may also leave bleaching in your lawn during its peak time to shine. 

Round-Up, or glyphosate, will also kill P. annua, but since it’s a non-selective herbicide, it’ll also kill any other plants it comes into contact with — including desirable turf species. 

Avenger Herbicide is my personal favorite. It’s also a non-selective herbicide, but it’s an organic weed spray made from citrus oils. A concentrate of 4 parts Avenger to 1 part water will usually kill P. annua in one or two applications. But like Round-Up, Avenger will also kill any other plants that it comes in contact with — including your lawn. 

How To Control Poa Annua

It takes more than a one-and-done approach to control Poa annua in lawns. One of the most aggressive weeds in the Poa species — which includes Poa infirma, P. trivialis, and Poa pratensisP. annua seeds lay dormant in the soil for several years before emerging and becoming new weeds.

Controlling this grassy weed — and other aggressive weeds invading areas of your lawn — requires constant maintenance, including chemical control, natural weed control methods, and lawn-friendly cultural practices.

Your best chance against Poa annua in your lawn is to apply frequent weed control practices and proper maintenance routines.

How to Stop Poa Annua Seeds Before they Start

The most effective way to control P. annua is to apply a pre-emergent herbicide such as Prodiamine (liquid or granular) or Dithiopyr (generic Dimension) to the lawn in late summer, towards the end of August, or when soil temperatures drop to around 70 degrees. For Massachusetts residents, you should apply Prodiamine to your lawn by the third week of August.

With a fall pre-emergent strategy, you will not be overseeding your lawn. That means no core aeration and no spreading of weed seeds. Both Prodiamine and Dimension will help prevent Poa annua seeds from germinating, but it’ll do the same to your new turf.

Overseeding is my favorite lawn care pastime of the cool season, but your best bet for reducing annual bluegrass in your turf over time will be to bypass overseeding and apply a pre-emergent to your lawn to control P. annua seeds instead.

Poa Annua Control – Cultural Practices

A few cultural practices for weed control will go a long way toward reducing the infestation of Poa annua and other grass weeds in your lawn.

Don’t Overwater

Poa annua dies off in the late summer when temperatures are consistently above 80 degrees. Since annual bluegrass is a plant with shallow roots and likes shady areas when it’s hot out, watering your lawn deeply and infrequently will help prevent P. annua and similar weeds from thriving in your turf.

Mow Your Grass Tall

Poa annua is a short annual grass. If you follow best practices for most cool-season turf types and mow your lawn between three to four inches high, you’ll make it more difficult for this plant to survive in your turf.

Poa Annua Pre-Emergent Herbicides

Poa Annua Weed Killer (Non-Selective, Post-Emergent Herbicides)

Poa Annua Frequently Asked Questions (FAQ)

When does Poa annua germinate?

Poa annua germinates in the late summer and early fall when soil temperatures start to fall below 70 degrees.

How do I get rid of Poa Annua?

Since it’s a winter annual grass, the best way to control Poa annua is to apply a pre-emergent to your lawn in late summer or early fall, and again the following spring. This will help prevent the invasive weed from germinating. 

To get rid of and control Poa annua once it’s already established in your lawn, a non-selective herbicide like glyphosate will do the trick. Tenacity Herbicide will damage P. annua, although this isn’t listed on the label of weed grasses it’ll kill.

What’s the difference between Poa annua and Kentucky Bluegrass?

Poa annua and Kentucky bluegrass look very similar when the grasses begin to flower and seed. But while P. annua is an annual cool season plant, KBG a perennial. The seeds that shed from P. annua germinate in late summer or early fall, where the KBG seeds are sterile and do not germinate.

And while Poa annua appears as a lighter shade of green, KBG is known for its deep, dark green that sometimes appears blue.

What is another name for Poa annua?

Poa annua is also known as annual bluegrass, annual meadow grass, or just Poa.

What’s the difference between Poa Annua and Poa trivialis?

There’s a lot in common between Poa annua (annual bluegrass) and Poa trivialis (rough bluegrass.) Both plants exhibit clumping growth and a lighter shade of green, but the main difference between the two weeds is that P. annua is an annual grass, while Poa triv is perennial. 

Poa annua also flowers and produces seeds in late summer, whereas Poa triv generally does not. P. annua germinates in the early fall — usually in September — and survives overwinter in a vegetative state, only to emerge and thrive in your lawn the following early spring. 

Both of these grasses require cultural and chemical weed control practices to manage. 

Does Tenacity Kill Poa Annua (Annual Bluegrass)?

The label of Tenacity reads that both bentgrass and Poa annua are “sensitive to Tenacity applications.” We tried two applications of Tenacity with a non-ionic surfactant on P. annua and saw the weed turn white, then brown, and ultimately die. But this isn’t a guarantee that it’ll kill P. annua or similar weed species or prevent its weed seeds from shedding and germinating.

Does Tenacity Work as a Pre-emergent Against Poa Annua (Annual Bluegrass)?

The label of Tenacity reads that when used as a pre-emergent against weed species like Poa annua, it acts as a suppressant. It’s always best to use Prodiamine on your lawn in the late summer, and again the following spring to help prevent the germination of P. annua. But using Tenacity (Mesotrione) at seeding is a good measure to help control Poa annua.

Poa Annua Pre-Emergent Herbicides

Poa Annua Weed Killer (Non-Selective, Post Emergent Herbicides)


Poa Annua Frequently Asked Questions (FAQ)

When does Poa Annua germinate?

Poa annua germinates in the late summer and early fall when soil temperatures start to fall below 70 degrees.

How do I get rid of Poa Annua?

Since it’s a winter annual grass, the best way to control Poa annua is to apply a pre-emergent to your lawn in late summer or early fall, and again the following spring. This will help prevent the invasive weed from germinating. 
To get rid of and control Poa annua once it’s already established in your lawn, a non-selective herbicide like glyphosate will do the trick. Tenacity Herbicide will damage P. annua, although this isn’t listed on the label of weed grasses it’ll kill.

What’s the difference between Poa Annua and Kentucky Bluegrass?

Poa annua and Kentucky bluegrass look very similar when the grasses begin to flower and seed. But while P. annua is an annual cool season plant, KBG a perennial. The seeds that shed from P. annua germinate in late summer or early fall, where the KBG seeds are sterile and do not germinate. And while Poa annua appears as a lighter shade of green, KBG is known for its deep, dark green that sometimes appears blue.

What is another name for Poa Annua?

Poa annua is also known as annual bluegrass, annual meadow grass, or just Poa.

What’s the difference between Pao Annua and Poa Trivialis?

There’s a lot in common between Poa annua (annual bluegrass) and Poa trivialis (rough bluegrass.) Both plants exhibit clumping growth and a lighter shade of green, but the main difference between the two weeds is that P. annua is an annual grass, while Poa triv is perennial. 

Poa annua also flowers and produces seeds in late summer, whereas Poa triv generally does not. P. annua germinates in the early fall — usually in September — and survives overwinter in a vegetative state, only to emerge and thrive in your lawn the following early spring. 

Both of these grasses require cultural and chemical weed control practices to manage. 

Does Tenacity Kill Poa Annua (Annual Bluegrass)?

The label of Tenacity reads that both bentgrass and Poa annua are “sensitive to Tenacity applications.” We tried two applications of Tenacity with a non-ionic surfactant on P. annua and saw the weed turn white, then brown, and ultimately die. But this isn’t a guarantee that it’ll kill P. annua or similar weed species or prevent its weed seeds from shedding and germinating.

Does Tenacity work as a Pre-emergent against Poa Annua (Annual Bluegrass)?

The label of Tenacity reads that when used as a pre-emergent against weed species like Poa annua, it acts as a suppressant. It’s always best to use Prodiamine on your lawn in the late summer, and again the following spring to help prevent the germination of P. annua. But using Tenacity (Mesotrione) at seeding is a good measure to help control Poa annua.

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