Poa Trivialis: How to Identify, Remove + Control It

Grassy and broadleaf weeds are stumbling blocks to growing a healthy lawn. They compete with turf for water, air, and nutrients and sometimes choke the lawn if not identified and controlled early enough.

Poa trivialis is identifiable by its light green coloration in the fall and spring. The leaves sometimes assume a reddish hue. Its folded buds, smooth leaves, and bumpy stems are the most striking features. Removing this colonizing grass on your lawn requires the use of herbicides such as Roundup.

However, preventing further growth requires you to keep a thick lawn that suppresses Poa trivialis seeds.

Poa trivialis identification?

Poa trivialis is a perennial cool-season weed in the northern lawns. It is also used for overseeding southern lawns. Poa trivialis is from the Poaceae family and was introduced to the north from Europe.

You can identify Poa trivialis:

By color

Rough bluegrass is challenging to identify when young. However, it is noticeable after establishing and declining around summer. Poa trivialis has to light green conspicuous leaf blades among dark green cool-season grasses. The plant becomes dormant and turns brown in late summer, leaving bare brown spots on the lawn. Poa trivialis stems and roots remain active and recover in fall. You can easily mistake Poa trivialis for diseased lawn grass.

Physical characteristics

Poa trivialis has distinct midrib, boat-shaped, hairless leaves, and no auricles. The ligule is membranous and pointed. Poa trivialis has a folded vernation; leaves emerge folded from the bud. The seedhead is a panicle with spikelets with two to three flowers. Poa trivialis doesn’t produce a seedhead when it’s mowed.

 Poa trivialis is often mistaken for Poa annua. Yet, they are different. Poa trivialis leaves are light green and boat-shaped. Also, it is stoloniferous, while Poa annua has a bunch of types of growth habits.

 Poa trivialis spreads by seeds and stolons and gets aggressive in shaded lawns.

Why do I have Poa trivialis on my lawn?

Poor lawn conditions such as low mowing heights, high shade, light, infrequent watering, and compacted soils encourage Poa trivialis seeds to germinate and thrive on the lawn.

Poa trivialis produces numerous seeds in the reproductive window.

Dormant Poa trivialis seeds could be lying unnoticed on the lawn for several years. The seeds germinate in the spring or fall when the soil is cool and moist and spread on the property. Pets, winds, and human feet carry weed seeds from infested lawns to other lawns.

Rough bluegrass seeds are smaller than the seeds of other cool-season grasses. Sometimes they are introduced as a contaminant when overseeding existing grass.

Low mowing height

Weed seeds require sunlight to germinate and spread on the lawn. Mowing grass shorter than 2 inches allows sunlight to penetrate the soil, encouraging the seeds to grow.

It’s also possible the Poa trivialis is growing on your lawn because you mow your grass shorter than 2 inches. 

Watering lightly and more often

Irrigating the lawn lightly and frequently saturates the soil. As a result, the grassroots weaken and become vulnerable to diseases and weeds invasion. Waterlogged soils also wash away nutrients from the soil, making the soil nutrient-scarce for the healthy growth of desirable grass.

Compact soils

Tight soils suffocate the grass by blocking water, air, and nutrients from penetrating the grassroots. Therefore, the soil accumulates toxic gases like Carbon dioxide from the roots.  Lack of air circulation limits the plant cells’ function, and eventually, the grass dies. All weeds are opportunistic, and whenever turf thins and weakens, they invade the lawn quickly.

Push a 6-inch long screwdriver into the lawn soil to check the compactness level. The screwdriver feels challenging to penetrate and comes dry with no soil particles sticking on its sides when inserted in compact soil.

How do I get rid of Poa trivialis?

Removing Poa trivialis from the lawn is challenging. The weed is unnoticeable when young and only identified after establishing and spreading. Since it’s a perennial grass, it regrows after several herbicide treatments. Poa trivialis is impossible to remove from shaded areas with good rainfall because it thrives in full shade.

Getting rid of Poa trivialis from the lawn is done using post-emergent herbicides, followed by turf management to prevent the weed from regrowing.

Apply  Velocity herbicide

It’s challenging to get selective herbicides that kill rough bluegrass from cool-season lawns.  Velocity is the only selective post-emergent herbicide. However, it is limited to golf courses and sod farms.

 Velocity requires multiple applications to kill the weeds. Sometimes it’s not effective because the Poa trivialis will regrow. Furthermore,  Velocity inhibits plant growth if it accidentally spills on desired grass, taking two weeks to recover from the damage.

For more effectiveness, treat Poa trivialis with  Velocity herbicide in spring and mid-summer when the average day temperature exceeds 75oF but less than 95oF to avoid damaging the existing grass.

To remove Poa trivialis faster from the lawn, apply  Velocity herbicide at a rate of 6.0 oz per acre every 14 to 21 days up to four times. For slow removal, apply the herbicide at a rate of 2.0 oz per acre every 7 to 14 days up to four times. Temperatures between the applications should be more than 75oF.

Apply Roundup herbicide

Roundup is a non-selective post-emergent herbicide used to control weeds and is acceptable in home lawns and athletics fields. It has glyphosate, a chemical substance that saturates and dries grass, turning them brown and killing them.

Since Roundup is non-selective, it also kills the lawn’s existing grasses if it falls on them. Apply Roundup herbicide in spring or late summer for small yards. Late summer Roundup herbicide applications are reserved for large infested areas.

Roundup herbicide requires multiple applications over the infested areas to kill Poa trivialis.

After applying non-selective herbicides to remove Poa trivialis, overseed with new grass seeds, or install sod to the treated areas.

What kills Poa trivialis?

Post-emergent herbicides are the only chemical solutions that kill Poa trivialis from home lawns. But, they are non-selective and will kill the desired turfgrass on the property.

Tenacity herbicide

Syngenta’s Tenacity weedkiller kills broadleaf weeds and grassy weeds. Tenacity can be used as a pre-emergent to kill weed seeds as they emerge from the soil. It’s also used as a post-emergent herbicide to kill established weeds. 

Tenacity kills weeds like crabgrass, ground ivy, henbit, wild carrots, carpetweed, chickweed, clover, and yellow nutsedge from the lawn.

The active ingredient in Tenacity herbicide is Mesotrione. The roots, shoots, and leaves absorb the herbicide, which blocks enzymes and inhibits photosynthesis. The weeds turn pale and die, leaving grasses. 

Tenacity is best applied in the spring or fall when the air temperature is below 80oF. The product takes between 14 and 21 days to kill the weeds. Treated lawns with tenacity are safe for kids and pets.

Roundup concentrate herbicide

Roundup herbicide is non-selective and contains glyphosate as the active ingredient. It kills more than 200 weeds, including grassy and tough broadleaf herbicides like dandelions, crabgrass, ground ivy, and Poa trivialis.

Roundup is a concentrate and should be mixed with water before spraying on the leaves and stems of the weed—mix 2.5 ounces of the concentrate with 1 gallon of water in a spray bottle. The herbicide contacts the weeds, rots, and kills them within 2 to 4 days. The treated weeds turn brown and die. Reseed the lawn after treating with a roundup to cover the bare spots.

Ortho WeedClear Weed Killer for Lawn Concentrate

Ortho weed killer concentrate controls grassy and broadleaf weeds like dandelions, chickweed, clover, ground ivy, and dollarweed. It doesn’t harm the grass if used as directed.

The concentrate is applied on young actively growing weeds using a sprayer on the unwanted plants and absorbed by the plants’ leaves and stems. Pets and kids can freely use the lawn after treatment with the herbicide. 

Tips to control and prevent bluegrass off your lawn

 Poa trivialis weeds are tough to remove. They regrow several years later, even after multiple herbicide treatments.

Because the weeds prove challenging to identify early and are only noticed after establishing, proper turf care is essential to prevent them from regrowing. Here are the best cultural practices to prevent and control Poa trivialis from setting on the lawn.

Mow lawn higher

Cutting grass shorter than 2 inches allows sunlight to reach Poa trivialis seeds, encouraging them to germinate on the lawn.

On the other hand, cutting the grass higher than 3 inches blocks sunlight and discourages Poa trivialis seeds from growing.

Always mow your grass higher than 3 inches.

Water the lawn deeply and infrequently

Grassroots need sufficient water to grow stronger and extend deeply into the ground. Watering the grass lightly often weakens the roots, making them susceptible to diseases and weeds invasions.

Watering the grass profoundly and infrequently is a reverse mechanism that encourages the grassroots to grow stronger to withstand weeds and disease invasion.

Water the lawn only when the grass needs water. Check for dry footmarks on the grass or when the grass shows signs of stress to know when to water the lawn. Irrigate with 1 inch and above depending on your turfgrass watering needs.

Aerate compact soils

Check if your lawn soil is compact and aerate it. Use a core aerator to remove small plugs of soil to create spaces for the passage of air, water, and nutrients to the grassroots to grow them more robust.

 You can also use a spike aerator to make small spaces for less compact soils. Aerate once per year in heavy clay soils getting high foot traffic. Aerate after three years for loose sandy soils.

Compact soil prevents water, air, and nutrients from reaching the grassroots, weakening and making the grass prone to diseases and weeds.

Fertilize the lawn

Apply nitrogen fertilizers in the fall when the grass is actively growing. Slow-release fertilizers are preferred to fast-release fertilizers as they feed the lawn longer.

Fertilizers add more nutrients to the soil to boost the turf’s health. When grass gets little to no nutrients, it grows weak, unhealthy, and less competitive with weeds and diseases.

References

  1. University of Maryland Extension: Roughstalk Bluegrass.
  2. Purdue University: Control of Poa Annua and Poa trivialis in Lawns.

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