Poa Annua (Annual Bluegrass) is best controlled with a program that combines a pre-emergent herbicide to prevent the weed from sprouting in fall, followed by a post-emergent application to kill any Poa Annua that appears. Below we’ll cover the best products and methods for both these tactics.
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How Do You Stop Annual Bluegrass? Pre-Emergent Schedule
Like the name suggests, Annual Bluegrass is an annual weed. This means that it grows for a season, casts its seeds, and then dies. So, the yearly infestation in your yard comes from seeds, not from established plants. To stop Poa Annua from invading your lawn, use a pre-emergent herbicide. This herbicide will remain in the soil for 6–12 weeks. During this time, it will kill any Poa Annua seeds as they sprout:
- Annual weeds, such as Poa Annua sprout from seed each year.
- Poa Annua commonly sprouts in the fall, as summer temperatures cool.
- Use this pre-emergent in the fall, once soil temperatures come down to 70℉ (21℃) for 2–3 days.
- The best time for fall pre-emergent application is typically early September.
- In some regions, Poa Annua may sprout in spring as well as fall.
- Perform a pre-emergent application in spring, when soil temperatures rise to 55℉ (12℃) for 2–3 days, typically in March.
For additional winter weed control, consider performing 2 applications of pre-emergent in the fall. Apply pre-emergent first in early September, then perform a second application 30 days later. Correct pre-emergent timing is essential to get the most out of your weed-stopping products.
What Herbicide Will Kill Poa Annua? 5 Best Post-Emergent Controls
An effective post-emergent herbicide for Poa Annua is one that kills these grassy weeds without doing harm to your lawn. The methods and products here are effective at killing mature Poa Annua currently invading your yard.
Although Poa Annua is not listed on the Tenacity label, studies conducted by the Universities of Nebraska, Illinois, and Purdue have shown success when using Tenacity to kill Poa Annua. One of the benefits of Tenacity is that it is safe for use even when overseeding lawns in fall, as it will not harm desirable grass seedlings. If you plan to overseed your lawn in fall, use Tenacity to kill any Annual Bluegrass that comes up along with your new grass.
For best results: Apply 3 times beginning in September/October, with 2 weeks between applications.
To control Poa Annua that has sprouted in St. Augustine and Centipede grass lawns, use this weed killer with Atrazine. Herbicides with Atrazine will both kill Poa Annua and work as a pre-emergent herbicide that prevents additional Annual Bluegrass seeds from sprouting. It can be used in spring, summer, or fall to prevent Poa Annua and broadleaf weeds at the same time.
For best results: Apply only to St. Augustine and Centipede grass lawns. Atrazine is harmful to other grass types like Bermuda and Kentucky Bluegrass.
Roundup is a non-selective herbicide, meaning it will kill all plant types, including your desirable turf grass. This makes it better for killing Poa Annua than herbicides with Quinclorac. However, it’s important to note Glyphosate, the active ingredient in Roundup, only attacks actively growing plants. This means you can use Roundup to kill Poa Annua in 2 ways:
- If your lawn grass is actively growing (green), spot-treat Poa Annua clusters by carefully spraying Roundup on Poa Annua only.
- If your lawn grass is dormant (brown), Roundup won’t hurt it. You can spray green tufts of Poa Annua to kill them and any dormant grass exposed to Roundup will not be harmed.
In regions where warm-season grass is invaded by Poa Annua in fall, the invasive Annual Bluegrass often stays green throughout the winter. This is the perfect time to attack the Poa Annua with Roundup.
For best results: Spray Poa Annua in dormant yards, or use cardboard to shield actively growing grass from overspray.
Prograss EC is an industrial herbicide typically used for killing Poa Annua in golf courses and sports field settings. This post-emergent herbicide is absorbed through Poa Annua blades and is effective at killing the pest grass in summer, winter, or spring.
For best results: Apply 3 times in fall, with 2 weeks between applications.
Hand Weeding/Cultural Practice
In small yards, hand weeding Poa Annua is an effective way to remove the weed to the roots without adding any herbicide to soils. This will protect your grass be eliminating chemicals completely. If you have had the opportunity to spread a pre-emergent herbicide, it’s likely that very little Poa Annua will sprout. This makes hand weeding much more manageable.
Annual weeds, like Poa Annua and crabgrass, more easily invade sparse or struggling yards. Cultivate a healthy yard with regular mowing, watering, and fertilization to keep weeds out and reduce Poa Annua invasion.
For best results: Make sure to remove Poa Annua down to the roots when hand weeding, to prevent regrowth.
How Do You Kill Poa Annua Without Killing Grass?
To kill Poa Annua (Annual Bluegrass) while keeping your lawn safe from harm, use the following methods:
- Apply pre-emergent herbicide in early fall (September) to keep Poa Annua from sprouting.
- Use Tenacity herbicide to treat a lawn infested with Poa Annua. This herbicide won’t harm your turf grass.
- Apply an Atrazine-based weed killer to eliminate Poa Annua in St. Augustine or Centipede grass lawns.
- Use Roundup to perform spot treatments of Poa Annua.
- Spray Roundup on green Poa Annua growing among dormant grass (dormant grass won’t be harmed by Roundup).
- Hand weed Poa Annua, removing it down to the roots.
- Practice good cultural practices by watering, fertilizing, and mowing your yard during the growing season. A thick lawn resists invasion by Annual Bluegrass.
When using herbicides to prevent or kill Poa Annua, make sure to review all manufacturer guidelines and apply products at product label rates. When used properly, these methods will stop the Poa Annua plant from taking over your yard and keep your turf grass safe from harm.