How to get rid of annual bluegrass weeds?

Annual Bluegrass Control

Annual bluegrass (Poa annua) is a cool-season, annual grass that spreads by seed. Annual bluegrass has a tufted habit with a bright green leaf color and fine texture. It is native to Europe and is found worldwide.

Annual bluegrass grows with a clumping growth habit.
Millie Davenport, © 2010, HGIC, Clemson Extension

Annual bluegrass has a smooth leaf blade with a boat shaped tip.
Joseph M. DiTomaso, University of California – Davis, Bugwood.org

Annual bluegrass has fuzzy, white seed heads that appear in April.
Millie Davenport, © 2010, HGIC, Clemson Extension

Annual bluegrass has smooth leaves with a boat-shaped tip. It produces greenish white seed heads throughout its life cycle with the majority appearing during the spring months. It can be found growing in a wide variety of conditions, but prefers areas with moist and/or compacted soil.

Before starting a weed control program, homeowners should realize that complete eradication of annual bluegrass (or any weed) from the landscape is not practical. A more realistic approach is to manage (not eradicate) the weed by reducing the infestation to a tolerable level.

Control in Lawns

Maintaining the health and density of the lawn is the best method for preventing a weed problem. Proper mowing height, irrigation, and fertilization of the turfgrass are the best defenses against weeds. For more information on these topics, see the following fact sheets: HGIC 1201, Fertilizing Lawns; HGIC 1205, Mowing Lawns; and HGIC 1207, Watering Lawns.

If annual bluegrass does become a problem in a turfgrass area, it can be dug up easily before it is well established. Large patches may be difficult to dig up, and an herbicide may be required. If an herbicide treatment is chosen, it is best to start treatments in the fall before seeds germinate.

Pre-emergence herbicides should be applied to well-established lawns in late summer or early fall when temperatures drop to a daytime high of 75 °F for four consecutive days. For most products, a second application needs to be applied 8 to 10 weeks later in the fall for continued control.

Because herbicide resistance by annual bluegrass has recently emerged, it is best to rotate among different pre-emergence herbicides for the best weed grass control. Many of the common, pre-emergence herbicides that are available to the homeowner are closely related for how they prevent weed seed germination. Therefore, when applying subsequent herbicides, they must be ones that each have a different mode of action. There are three different mode of action groups of pre-emergent herbicides, which are available in granular form for ease of application. They are all capable of giving good to excellent control of annual bluegrass. The most common products are in group 1, and these include benefin, dithiopyr, oryzalin, pendimethalin, prodiamine, and trifluralin. The second chemically different group includes isoxaben and indaziflam. The third group includes oxadiazon. Table 1 lists granular products within these three mode of action groups. All of the herbicides are labeled for use on centipedegrass, zoysiagrass, bermudagrass, St. Augustinegrass, and turfgrass tall fescue lawns, except for oxadiazon, which cannot be used on centipedegrass.

Note that if any of these weed-grass pre-emergence herbicides are applied in the fall on a tall fescue lawn, these lawns cannot be over-seeded with additional fescue that fall. However, spring over-seeding with tall fescue is possible around March 1st. Read the product label for its duration of control.

Apply each granular product at its label rate for Poa annua control and water in the product after application. Examples of products for use in residential lawns in homeowner sizes are listed in Table 1.

There are pre-emergence herbicides for sale that combine nitrogen-containing fertilizers along with the herbicide. However, the best time to apply the pre-emergence herbicide is not usually the best time to apply the fertilizer. Only those with 0-0-7 fertilizer (7% potash) are listed, as these can be applied at the correct time for best weed prevention.

Table 1. Pre-emergence Herbicides for Control of Annual Bluegrass in Lawns.

CAUTION: Pre-emergence herbicides are not selective and can prevent the development of turfgrass seeds and the development of roots on turfgrass sprigs, sod, and plugs. Read the label for time to wait before seeding a treated area. It is best to wait for six months after starting a new lawn before pre-emergence herbicides are applied.

Atrazine is a very different herbicide that can be applied only to St. Augustinegrass and centipedegrass for both pre- and post-emergence control of annual bluegrass. Apply atrazine in November and again in early January. Atrazine can be applied up to two times per year. It should NOT be applied to newly seeded lawns due to the detrimental effect it has on seed development. Delay atrazine applications to newly sodded and sprigged lawns until they are well established and actively growing. Do not apply atrazine to lawns that are greening up during spring, as severe turfgrass injury may occur. Examples of atrazine products for residential lawns in homeowner sizes are:

  • Hi-Yield Atrazine Weed Killer Concentrate
  • Southern Ag Atrazine St Augustine Weed Killer Concentrate
  • Image for St. Augustinegrass & Centipedegrass with Atrazine Concentrate
  • Spectracide Weed Stop for Lawns – for St. Augustine & Centipede Lawns Ready to Spray (a hose-end spray bottle)

CAUTION: Atrazine can travel through soil and enter ground water; therefore read the label for all environmental precautions. Users are advised not to apply atrazine to sand or loamy sand soils where the water table (groundwater) is close to the surface and where these soils are very permeable, i.e., well-drained. Do not apply atrazine herbicide within two times the width of the drip line of desirable hardwood trees and shrubs.

Non-selective herbicides such as glyphosate can be used for spot treatments; however, nearby desirable grasses and plants can be severely injured. Glyphosate is most effective when applied to young weeds in November. Annual bluegrass plants that are found growing in April and May will dieback as temperatures rise, so it is not necessary to treat them at that time. Examples of glyphosate products in homeowner sizes are:

  • Roundup Original Concentrate,
  • Roundup Pro Herbicide,
  • Martin’s Eraser Systemic Weed & Grass Killer,
  • Quick Kill Grass & Weed Killer,
  • Bonide Kleenup Weed & Grass Killer 41% Super Concentrate,
  • Hi-Yield Super Concentrate,
  • Maxide Super Concentrate 41% Weed & Grass Killer,
  • Super Concentrate Killzall Weed & Grass Killer,
  • Tiger Brand Quick Kill Concentrate,
  • Ultra Kill Weed & Grass Killer Concentrate,
  • Gordon’s Groundwork Concentrate 50% Super Weed & Grass Killer,
  • Zep Enforcer Weed Defeat III,
  • Eliminator Weed & Grass Killer Super Concentrate,
  • Monterey Remuda Full Strength 41% Glyphosate,
  • Knock Out Weed & Grass Killer Super Concentrate,
  • Southern States Grass & Weed Killer Concentrate II,
  • Total Kill Pro Weed & Grass Killer Herbicide,
  • Ace Concentrate Weed & Grass Killer.

Note: Once annual bluegrass has been eliminated in turfgrass, bare spots will be left behind. To prevent the invasion of new weeds in these bare spots, plan to fill them in with sod, plugs, or sprigs of the desired turfgrass at the appropriate planting time. In some areas of South Carolina, annual bluegrass is becoming resistant to glyphosate applications. In this case, a burn down application of d-limonene (citrus oil), as in Avenger Weed Killer Concentrate for Organic Gardening, will kill everything where sprayed. However, the warm season turfgrasses will likely regrow from the roots and rhizomes. For more information on renovating a lawn, see HGIC 1204, Lawn Renovation.

Control in Vegetable Gardens

When planning a vegetable garden, it is best to attempt to treat weeds before tilling the soil. Tilling can break up and spread weed seed throughout the garden plot. Some methods used to reduce weeds in the vegetable garden include hand pulling, hoeing, mulching, and applying post-emergence herbicides.

Hand pulling or hoeing weeds is only a practical choice for small garden plots. If hand pulling is chosen, be sure to work when the soil is moist so roots can be removed easily. When cultivating between the rows to control weeds, use care not to damage the roots of crops.

Organic mulch (such as pine needles, old hay, or grass clippings) can be used in the garden to help suppress annual bluegrass development. Before laying the mulch, apply a layer of six to eight wet newspaper sheets to act as a weed barrier. The newspaper layer prevents weed development by blocking light to the weeds underneath, preventing their growth. Best of all, the newspaper should decompose before the following spring. To prevent low oxygen levels in the root zone, keep organic mulch levels at a maximum of 3 inches. For more information on mulching a vegetable garden, see HGIC 1253, Controlling Weeds by Cultivating & Mulching.

Pre-emergence herbicides can be used in the fall garden to prevent weed germination. Trifluralin, also called by the trade name Treflan, can be used on some vegetable crops. It should be applied to prepared soil and incorporated 2 inches deep before planting. NOTE: Trifluralin is not safe to use on every garden plant. See the herbicide label for application timing and safety for each crop species, the proper application rate, and watering-in instructions. Examples of products containing trifluralin for use in home vegetable gardens are:

  • Preen Garden Weed Preventer Granules Containing Treflan
  • Hi-Yield Herbicide Granules
  • Monterey Vegetable & Ornamental Weeder – Weed & Grass Preventer Concentrate
  • Miracle-Gro Garden Weed Preventer Granules

Lastly, a non-selective, post-emergence burn down herbicide can be used to treat the garden plot before planting. Avenger Weed Killer Concentrate for Organic Gradening contains d-Limonene (citrus oil), can be applied to the garden plot up to 3 days prior to planting. Check the label for precautions for individual crops. Burn down sprays are most effective when weeds are actively growing, so do not apply during extreme heat, cold or drought conditions.

Control in Landscape Beds

In landscape beds, annual bluegrass can be hand dug or controlled with an herbicide. As mentioned previously, it is best to prevent the invasion of annual bluegrass by maintaining optimum cultural conditions and using a 3-inch mulch layer to block weed development. Once annual bluegrass has made its way into the landscape bed, an herbicide may be necessary if hand pulling or hoeing is not practical.

Pre-emergence herbicides can be used to prevent weed germination in the fall. Trifluralin, also called by the trade name Treflan, can be applied around certain landscape plants. Read the herbicide label for a full list of plant species that are tolerant, the proper application rate, and watering-in instructions. Examples of products containing trifluralin for use in home landscapes are:

  • Preen Garden Weed Preventer Granules
  • Hi-Yield Herbicide Granules Containing Treflan
  • Monterey Vegetable & Ornamental Weeder – Weed & Grass Preventer Concentrate
  • Miracle-Gro Garden Weed Preventer Granules

Dithiopyr is another excellent pre-emergence herbicide for use around many ornamental landscape plants to prevent weeds. Read the herbicide label for a full list of plant species that are tolerant, the proper application rate, and watering-in instructions. Examples of products containing dithiopyr for use in home landscapes are:

Additionally, combination products that contain isoxaben and trifluralin, such as Snapshot 2.5 TG Granules, can be used safely around many established ornamentals for annual bluegrass control. Read the herbicide label for a full list of plant species that are tolerant, the proper application rate, and watering-in instructions.

Glyphosate can be used for spot treatments around ornamental plants. However, glyphosate is a non-selective herbicide that can harm any plant and should be used with caution. Do not allow glyphosate spray mist to contact ornamental foliage or stems, as injury will occur. For examples of glyphosate products in homeowner sizes, please see list in the “Control in Lawns” section. As with all pesticides, read and follow all label instructions and precautions.

Dealing With Annual Bluegrass in Your Lawn

Pretty much everyone is familiar with the most famous member of the Bluegrass family, Kentucky Bluegrass (Poa pratensis). Considered the Cadillac of lawn grasses, Kentucky Bluegrass is the most widely used turf species in the U.S. thanks to its dark-green color, lush texture, and thick spreading growth habit. And like some families, the Poa family has a black sheep. Poa annua, commonly known as Annual Bluegrass, is a bit of a misfit in the Bluegrass family. Unlike its more well-known cousin, Annual Bluegrass is not desirable in lawns. In fact, it’s considered a stubborn weed that can spoil the consistency, color, and uniformity of an otherwise beautiful lawn. While Annual Bluegrass is a difficult weed to control and almost impossible to completely eradicate, it is possible to manage the population down to a tolerable level by following some simple cultural control practices.

What Does it Look Like, and Why is it Such a Problem?

Annual Bluegrass is a clump-forming cool-season annual grass that begins germinating in autumn, goes dormant during winter, and ends its life cycle the following spring. The problems associated with Annual Bluegrass become very apparent as it begins to grow and spread in Kentucky Bluegrass lawns. Color differences are usually the first thing that’s noticed. Unlike the deep, dark-green color of Kentucky Bluegrass, Annual Bluegrass has a much lighter, “green-apple” appearance that stands out. When left unmowed, Annual Bluegrass will grow 6 to 8 inches high, but thrives at shorter lengths. This makes it especially annoying on golf courses where it invades putting greens and disrupts the smooth surface. On top of these problems, Annual Bluegrass has a coarser leaf texture and produces unsightly seedheads. Each plant can develop and drop up to 100 seeds in just a couple months after germinating, giving this prolific seeder its true weed status.

Avoid Compacted Soils

It’s important to understand the conditions that will contribute to Annual Bluegrass growth in order to avoid infestations. First, Annual Bluegrass loves compacted soil. Regular core aerating helps eliminate this condition and improves the overall health and vigor of the lawn. It’s best to core aerate before Annual Bluegrass germinates in the autumn so cool-season lawns can recover as quickly as possible before Annual Bluegrass germination begins.

Avoid Overwatering

Second, Annual Bluegrass thrives in wet soil conditions. I came to understand this all too well during the summers I managed the estate of a high-profile client. At the end of their driveway they had a beautiful water feature that ensured the surrounding soil stayed constantly moist. It was in this area I came to know firsthand the annoyance of Poa annua. This was a unique situation, but in most instances this can be solved by watering deeply and infrequently instead of lightly and frequently. Overwatering is not only wasteful, but it provides Annual Bluegrass with perfect habitat.

Avoid Applying Excessive Fertilizer

Next, avoid applying excessive nitrogen fertilizer during peak Annual Bluegrass germination periods. Annual Bluegrass responds well to high nitrogen applications. These applications only help it spread and better its chances of surviving into winter and spring. Better yet, use a slow-release organic maintenance fertilizer instead of synthetic fertilizers. These organic fertilizers apply nutrients slowly and over time instead of short bursts. They also help improve the amount of organic matter in the soil.

Mow Lawn Higher During Peak Annual Bluegrass Season

Finally, mow your grass a little higher during peak germination times. Leaving grass just a bit longer will help shade and crowd out Annual Bluegrass. On the other hand, mowing your lawn short will stress your grass and encourage Annual Bluegrass growth. Also, while I usually recommend leaving grass clippings on the lawn to act as a natural fertilizer, when Annual Bluegrass is present it’s best to bag grass clippings. Removing grass clippings during Annual Bluegrass outbreaks will help stop the spread of weed seed.

Chemical Control as a Last Resort

Chemical control should be a last option and only for extreme problem areas. Preemergent herbicides offer some prevention, but will not get rid of existing plants. For preemergent herbicides, timing is crucial and depends on climate, temperature, and other factors. Look for a preemergent herbicide containing the active ingredients benefin and trifluralin. This should be applied in autumn generally when the daily high temperature drops to 75 degrees for several days. A second application can be applied 10 to 12 weeks later. For individual plants, a non-selective herbicide containing glyphosate will kill Poa annua, but also any other plant it touches. This option should only be used in pure stands of Annual Bluegrass or when starting over is the best decision. Remember, non-chemical solutions should always be your first choice.

We all have a few interesting characters somewhere in our family tree, and the Bluegrass family is no different. By following these simple practices we can ensure our lawns are not overrun by the weedy pest, Annual Bluegrass.

Saint Augustine Lawn Care

Annual Bluegrass is another ugly and unsightly weed in Saint Augustine grass and all other lawn types as well. Its bright green leaves and clumping characteristics can quickly overtake a lawn transforming what would otherwise be a beautiful lawn into a complete mess of weeds.

Annual Bluegrass will begin germinating underground about a month or more before Winter, and will start emerging from the soil and in our lawns at the beginning of Winter. Annual Bluegrass will continue to germinate, grow stronger, start clumping, and spreading as the winter months continue.

By the time Spring rolls around, the Annual Bluegrass is in full growth, easily outgrowing the Saint Augustine lawn and sitting above it in stark contrast to the lawn around it. This is also the time that Annual Bluegrass will begin going into full seed, making the Annual Bluegrass weed even uglier.

This same seeding will be planting out thousands of new Annual Bluegrass seeds into our turf for emergence in the following years. So if we have Annual Bluegrass this year, it will be worse next year, worse the year after, and so the lawn weed continues each year getting worse.

So if we have Annual Bluegrass in our Saint Augustine lawns, it must be treated as soon as possible.

Controlling Annual Bluegrass In Saint Augustine Lawns

Annual Bluegrass is actually a very easy weed to eradicate, but only if it’s done at the right time.

Annual Bluegrass weed herbicide is diluted with water in a watering can or spraying bottle as per manufacturers guidelines, and applied to the entire lawn and not just to the area which appears most affected.

Be sure to measure the lawn before treatment to ensure the herbicide correct dosage is applied to the lawn.

Once the Annual Bluegrass weed herbicide is applied to the turf, the lawn is then lightly watered, which takes the herbicide down to the roots of the Annual Bluegrass where it does its work.

We should then begin seeing the Annual Bluegrass die off within 2 weeks.

When To Control Annual Bluegrass

Annual Bluegrass must be treated at the right time of the year, otherwise the herbicide will have no effect whatsoever in eradicatiing the weed.

We have explained that Annual Bluegrass begins germinating underground about a month before winter, and that Annual Bluegrass herbicide acts on the roots of the weed, also underground.

With this in mind, Annual Bluegrass is best and most easily treated in the month prior to winter arriving, pre-emergent and before we can even see the weed. Past this time and we can still control Annual Bluegrass in the first one to two months of winter.

However, the later we go into winter and the more mature the Annual Bluegrass becomes, the more difficulty we will have in controlling it. Treatments done as late as the last month of winter may not even have any effect at all, while Annual Bluegrass treatments at the end of winter simply will not work, the weed will be just too strong and will easily outcompete the herbicide, resulting in no effect whatsoever. Plus the seeding for the following years has already completed.

A Plan To Control Annual Bluegrass

So the questions are… how can we eradicate Annual Bluegrass before we can even see it in our Saint Augustine lawn, and what should we do if we were too late in the season to apply the herbicide?

If we missed the window to treat Annual Bluegrass in early winter or just prior to winter, or even mid-winter, then do not attempt treatments, it will only waste our money.

Mark down in your diary for next year to treat the Annual Bluegrass one month before the next winter is due to set in.

Because if we had Annual Bluegrass in our Saint Augustine lawn this year, its a guarantee it will be worse next year, and so it must be planned for and treated properly.

Once the Annual Bluegrass begins to go into massive seeding towards the end of winter, the best thing we can do here is to mow the lawn with a rotary mower and catch the clippings. A rotary mower uses a sucking action to pull clippings off the turf and into the catcher, and will thus do the same for many, but not all Annual Bluegrass seeds. So we are actually making the problem a little less worse for next year.

Mow more regularly when necessary to ensure that no Annual Bluegrass is left to seed for too long between mowings, otherwise we’ll be allowing more seeds to fall back into the lawn for more weeds next year. Once the catcher is full, be sure to empty into the trash and not into the garden bed, because we don’t want to be moving our Annual Bluegrass problem from our Saint Augustine lawn and into our gardens.

Multiple Annual Bluegrass Treatments

We will notice that not all the Annual Bluegrass will die in the Saint Augustine lawn after a single treatment of Annual Bluegrass weed herbicide.

If this is the case then a second treatment can be undertaken after 3 to 4 weeks if we are still in the safe time period for controlling Annual Bluegrass.

We will also notice that even if we had wonderful success in treating Annual Bluegrass this year, that it will still emerge next year, and the year after. This is because not all weed seeds will germinate in a single year, but will instead stagger their emergence over several years as this gives the weeds their greatest chance for ongoing survival.

So be aware of this fact, and give another simple Annual Bluegrass treatment in the following years if necessary, and we’ll have our problem of Annual Bluegrass in our Saint Augustine lawn completely under control.

Poa Annua Control – Poa Annua Grass Treatment For Lawns

Poa annua grass can cause problems in lawns. Reducing poa annua in lawns can be tricky, but it can be done. With a little knowledge and a little persistence, poa annua control is possible.

What is Poa Annua Grass?

Poa annua grass, also known as annual bluegrass, is a annual weed that is commonly found in lawns, but can be found in gardens as well. It is rather difficult to control because the plant will produce several hundred seeds in one season, and the seeds can lay dormant for several years before sprouting.

The identifying characteristic of poa annua grass is the tall tasseled seed stalk that will typically stand up above the rest of the lawn and becomes visible in late spring or early summer. But, while this seed stalk can be tall, if it is cut short, it can still produce seeds.

Poa annua

grass is typically a problem in the lawn because it dies back in hot weather, which can make unsightly brown spots in the lawn during the height of summer. It also thrives during cool weather, when most lawn grasses are dying back, which means that it invades the lawn at these susceptible times.

Controlling Poa Annua Grass

Poa annua grass germinates in the late fall or early spring, so timing of poa annua control is critical to being able to effectively control it.

Most people choose to control poa annua with a pre-emergent herbicide. This is an herbicide that will prevent the poa annua seeds from germinating. For effective poa annua control, apply a pre-emergent herbicide in early fall and again in early spring. This will keep the poa annua seeds from sprouting. But keep in mind that poa annua seeds are tough and can survive many seasons without germinating. This method will work towards reducing poa annua in the lawn over time. You will need to treat your lawn for many seasons in order to rid it completely of this weed.

There are some herbicides that will selectively kill poa annua in lawns, but they can only be applied by certified professionals. Non-selective herbicides or boiling water will also kill poa annua, but these methods will also kill any other plants that they come in contact with, so these methods should only be used in areas where you wish to kill plants on a wholesale basis.

Note: Chemical control should only be used as a last resort, as organic approaches are more environmentally friendly.

Undesirable Bluegrasses: Poa annua & Poa trivialis

Poa trivialis is a light green grass that creates thick mats of stems, choking out areas of lawn. Because of the off color and rapid growth it is aesthetically unappealing, as are the large bare spots it can leave when it goes dormant in summer. The timing and appearance of the die-out can look like a fungal infection, and is often mistakenly treated as such.

This weed grass is actually intentionally used in some applications as a winter overseed (it makes a good winter putting surface for golf greens). Because of rough bluegrass’s intolerance of heat, it is not suitable for use in our area as a turf grass. Unfortunately it is often found unintentionally in shade grass seed mixes. Due to the size of the seeds, Poa trivialis cannot be removed in the screening process that normally removes unwanted seeds and has contaminated a large portion of grass seed shade blends. The seed is also often missed during visual seed quality testing due to its similarity to the seeds of perennial bluegrass. For these reasons it has become a common contaminant in shade grass seed blends and is likely to remain so for the foreseeable future. Even worse, there are not currently any selective herbicidal controls available for rough bluegrass.

Control

There are a few cultural practices that can reduce the chances of weedy bluegrasses becoming established in your lawn, but they will not fix an existing problem. Primarily this means maintaining a thick and healthy lawn that can out-compete these grasses and other weeds. This requires being careful not to mow too short, as taller turf grass shades the soil and prevents weed seed germination (it helps with all weed seeds, not just annual bluegrass). Grass cut too short is also stressed and less able to compete against weeds. It also requires proper watering by watering deeply and infrequently, preferably once weekly; frequent, shallow watering benefits shallow-rooted annual bluegrass while inhibiting the development of deep, healthy roots on fescue and other desirable turf grasses. Low areas that remain wet for extended periods also encourage weed bluegrasses, as does a shady lawn (Both weed bluegrasses are more tolerant of wet soil and shade than desirable lawn grasses.) Finally, proper rates and timing of fertilizer applications will help strengthen your lawn while not overly stimulating undesirable weeds.

While there are no selective herbicide solutions for rough bluegrass, it can be controlled with a non-selective herbicide like glyphosate (Roundup) applied in spring, though this will kill desirable grass also. The resulting bare areas can be reseeded in spring, provided you have adequate irrigation to support young grass plants through summer.

Another option is to use herbicide in the fall, once the rough bluegrass has re-sprouted in the cooler weather. This should be accompanied by an application of a pre-emergent herbicide in late August to prevent any seeds in the soil from sprouting. If you use this method to control rough bluegrass, fall seeding must be skipped as the pre-emergent will also prevent lawn grasses from germinating.

Once you get control of weedy bluegrasses, regular pre-emergent applications are necessary until your lawn is thick and healthy enough to prevent any seeds from germinating and getting established. Because these weeds are so widespread, constant monitoring is required to keep them from becoming a problem again in your lawn.

Putting Poa Annua in its Place

Poa Annua Prevention and Non-Chemical Control

Before moving to chemical controls, there are a few preventative maintenance practices homeowners can implement to allow their lawn to outcompete the annual bluegrass. Due to its shallow rooting system, the weed will thrive in areas of the lawn that are overwatered; therefore, homeowners should attempt to water deeply and infrequently so that the shallow rooting system is unable to obtain the water it needs. It can also be beneficial to raise the mowing height for the lawn, as Poa annua is a shorter plant, which gives the lawn a chance to choke out the weeds. Creating a lawn that is dense and healthy can prevent weed problems from occurring. This includes maintaining a proper mowing, irrigation and fertilization schedule to meet the needs of the turf so that thin or diseased patches that are more susceptible to weeds do not have the chance to develop. Weeds will struggle to compete against a maintained, established lawn. Visit Lawnifi.com to learn more about how Lawnifi™️’s proper fertilization schedule will help your lawn become nourished and strong. Our Fall Fertilizer Box contains one bottle of Boost, Maintain and Recover, which work together to help your lawn get over the stressful heat of the summer as well as prepare for winter dormancy. Lastly, apply a pre-emergent in the late summer or early fall to prevent Poa annua from germinating. As previously mentioned, Poa germinates in the fall when soil temperatures drop below 70 degrees. To learn more, visit our Fall Weed Control: Apply Your Pre-Emergent Now blog.

Annual Bluegrass Control in Residential Turfgrass

  • Cultural Control
  • Chemical Control
  • Managing Herbicide Resistance

Annual bluegrass (Poa annua L.) is a problematic winter annual weed in residential turf. Compared to most turfgrasses, annual bluegrass has a lighter green color, coarser leaf texture and produces unsightly seedheads. Contrary to its name, both annual (live for one season) and perennial (live for many seasons) biotypes of annual bluegrass may be found in turf. Perennial biotypes are more prevalent on closely mowed turf that receives frequent irrigation and high nitrogen fertilization. Perennial biotypes will be more prevalent in shady or highly trafficked areas with compacted soil. While the two biotypes may not be easily distinguished from each other, annual types are more upright in growth and produce more seed than lower-growing perennial types.

Annual bluegrass seed germinates in late summer/early fall once soil temperatures fall below 70° F. Seedlings grow and mature in fall, overwinter in a vegetative state and produce seed in spring. Annual bluegrass is a prolific seed producer and individual plants may produce hundreds of viable seed, even when closely mowed. Annual bluegrass flowers over several months in spring and produces seed that may remain dormant in soil for years before germinating. Annual bluegrass grows well under short day lengths and cool conditions, and may out-compete other turf species during late fall and early spring. Annual bluegrass often dies from summer stresses but may survive if irrigated and if pests are adequately controlled, especially for perennial biotypes.

Cultural Control

Several cultural practices can be utilized to control annual bluegrass in residential lawns. Deep and infrequent irrigation encourages turfgrass root development, which may improve the ability of desired grasses to compete with annual bluegrass in mixed stands. Withholding water until desirable turfgrass species exhibit initial drought stress symptoms can help reduce soil moisture for potential annual bluegrass infestations. Overwatering, especially in shady areas, may predispose the site to annual bluegrass invasion.

Practices that promote soil compaction should be avoided to promote turfgrass growth and competition with annual bluegrass populations. Core aerifications should be conducted during active turf growth and favorable periods for quick recovery. Voids left in turf with exposed soil following aerifications may permit annual bluegrass invasion during periods of peak germination. For cool-season grasses, fall aerfications should be timed before annual bluegrass germinates. Warm-season grasses should have enough time to recover from summer aerifications to promote dense, high quality turf prior to annual bluegrass germination in fall.

Nitrogen fertilization should be reduced during peak annual bluegrass germination and periods of vigorous growth. High nitrogen at these times encourages annual bluegrass spread and survival into winter and spring. Fertilizing dormant turfgrasses when annual bluegrass is actively growing may also exacerbate infestations and should be avoided.

Mowing height, frequency and equipment requirements vary among turfgrass species and practitioners should maintain turf under appropriate regimens for successful long-term culture (Table 1). Raising the mowing height during peak annual bluegrass germination may encourage turf competition to reduce potential infestations. Lower mowing heights may predispose turf to stress and reduce competition with annual bluegrass populations. Turfgrass should also be mowed frequently during periods of vigorous growth to prevent scalping. Scalping thins out turf and may enable weeds, such as annual bluegrass, to establish. While returning clippings is recommended to recycle nutrients to the soil, removal of clippings may be useful when annual bluegrass is present and producing seedheads. Removal of clippings at this time will reduce the spread of viable seed.

Chemical Control

Preemergence Control

Preemergence herbicides may prevent annual bluegrass seed germination. However, preemergence herbicides will not eradicate established plants and will not effectively control perennial biotypes of annual bluegrass from spreading vegetatively. Application timing of preemergence herbicides for annual bluegrass control is very important. Herbicides must be applied in late summer/early fall before annual bluegrass germination. A second application can be applied in winter to control later germinating plants. Fall-applied preemergence herbicides should not be used if reseeding or resodding is needed to repair areas of damaged turf within several months after herbicide applications.

Several preemergence herbicides used for summer annual weed control will effectively control annual bluegrass in fall and winter (Table 2). Fall applications of herbicides such as bensulide (Betasan), dithiopyr (Dimension), pendimethalin (Halts, Pendulum, others) and prodiamine (Barricade, others) may effectively control annual bluegrass. For herbicides, rates and application information, refer to the current edition of the Georgia Pest Management Handbook. Many preemergence herbicides are available under a wide variety of trade names and formulations and turf mangers should carefully read label directions before applications.

Atrazine (Bonus, Purge, others) is labeled for centipedegrass, zoysiagrass, St. Augustinegrass and bermudagrass. Atrazine can be applied to actively growing and dormant centipedegrass or St. Augustinegrass but bermudagrass can be injured if treated while actively growing. Simazine (WynStar, others) may be applied to actively growing bermudagrass, centipedegrass, St. Augustinegrass and zoysiagrass lawns. Atrazine and simazine have excellent preemergence activity on annual bluegrass but soil residual is generally shorter (four to six weeks) compared to aforementioned herbicides. Several atrazine and simazine products are not labeled for residential lawns and turf managers should check labels for further information before use.

Most preemergence herbicides will provide similar initial efficacy if applied before annual bluegrass germination and sufficient rain or irrigation is received. Preemergence herbicides require incorporation from irrigation or rainfall so that weeds may absorb the applied material. In order to effectively control annual bluegrass, preemergence herbicides must be concentrated in the upper 0.25 to 0.33 inch of the soil profile. Retention on leaf tissue can be avoided by irrigating turf immediately after application for effective soil incorporation and herbicide activation.

Preemergence herbicide applications on non-irrigated sites have less potential for residual control, compared to irrigated turf, from product loss, poor soil incorporation and failure to activate the herbicide. Practitioners should return clippings on non-irrigated sites to help move potential herbicides remaining on leaf tissue to the soil. If clippings are collected as part of routine maintenance, practitioners should consider returning clippings until at least 1/2 to 1 inch of rainfall is received. Granular products may also be applied to non-irrigated sites for better soil incorporation than liquid formulations. Granular products may be easier to handle and apply with less equipment necessary than sprayable formulations. Granular herbicides should be applied when morning dew is no longer present to avoid interference from leaf tissue.

Postemergence Control

Annual bluegrass may be selectively controlled with postemergence herbicides (Table 3). Practitioners managing warm-season grasses have more options for selective postemergence annual bluegrass control than cool-season grasses. Foramsulfuron (Revolver) and trifloxysufluron (Monument) are labeled for bermudagrass and zoyiagrass residential lawns and other sites (see the current edition of the Georgia Pest Management Handbook). Efficacy of these herbicides generally increases under warm temperatures in spring compared to winter and non-ionic surfactants may enhance efficacy.

Atrazine (Bonus S, others) may also be applied to dormant bermudagrass and actively growing centipedegrass, St. Augustinegrass and zoysiagrass for selective postemergence annual bluegrass control (see the current edition of the Georgia Pest Management Handbook). Atrazine may provide erratic control of annual bluegrass but may control other grassy and broadleaf weeds. Actively-growing bermudagrass is sensitive to atrazine and applications are recommended only during the late fall and winter months. Simazine (WynStar, others) may be applied to actively growing bermudagrass, centipedegrass, St. Augustinegrass and zoysiagrass. Simazine provides excellent postemergence control of annual bluegrass during winter and spring months. See product labels for registered areas of atrazine and simazine products before using for postemergence annual bluegrass control.

Sulfosulfuron (Certainty) and metsulfuron (Blade or Manor) may control young annual bluegrass plants but do not control mature populations (see the current edition of the Georgia Pest Management Handbook). These herbicides are labeled for bermudagrass, centipedegrass, St. Augustinegrass and zoysiagrass. Sulfosulfuron can also be applied to bahiagrass and seashore paspalum. Repeat application may be required for complete annual bluegrass control in warm-season grasses.

Dormant bermudagrass may be treated with nonselective herbicides, such as glyphosate (Roundup, Touchdown, others), glufosinate (Finale) and diquat (Reward) (see the current edition of the Georgia Pest Management Handbook). These herbicides will injure or kill existing vegetation, including annual bluegrass, and managers should only spray at peak dormancy when no green turfgrass foliage is observable. Nonselective herbicides should only be applied to completely dormant bermudagrass. Applications during early spring may delay greenup with significant turf injury.

Selective annual bluegrass control options in cool-season lawns are limited. Ethofumesate (Prograss) controls established annual bluegrass in perennial ryegrass, tall fescue and dormant bermudagrass (see the current edition of the Georgia Pest Management Handbook). Two or three ethofumesate applications may be applied in late fall at three- to four-week intervals. Annual bluegrass control may be seen that fall, but control is usually observed the following spring. Annual bluegrass control with ethofumesate may vary greatly over years depending on environmental conditions. Spot treatments of nonselective herbicides are generally the most effective treatment regimen for annual bluegrass control in cool-season grasses.

Managing Herbicide Resistance

Annual bluegrass is a genetically diverse species and various biotypes present in turf may have differential responses to herbicides. Repeated use of one herbicide chemistry may effectively control annual bluegrass but resistance may develop in local populations if herbicides with different modes of action are not incorporated in to management regimens. Herbicide resistance is the survival of a segment of the population of weeds following a herbicide dosage lethal to the normal population. Resistance occurs from repeated use of the same herbicide or mode of action over years and may be a concern with problematic annual weeds, such as annual bluegrass.

Triazine herbicides, atrazine and simazine, have been popular products in residential turf due to the wide spectrum of weeds controlled as pre- or postemergence treatments. Resistance in weed populations has been reported with these herbicides and may contribute to inconsistent efficacy for annual bluegrass control in warm-season turf. Resistance to other chemistries used for annual bluegrass control, such as sulfonylureas and dinitroanilines, has been widely reported in weed populations and rotation of herbicides with different modes of action should be considered when planning annual bluegrass control programs in residential turf.

Table 1. Mowing requirements for residential turfgrasses in Georgia.
Mowing Requirements for Turfgrasses
Species Mower Type Height (inches) Frequency (days)
Bermudagrass
Common
Hybrid
Rotary/reel
Rotary/reel
1 to 2
0.5 to 1.5
5 to 7
3 to 4
Centipedegrass Rotary 1 to 2 5 to 10
Perennial Ryegrass Rotary/reel 0.5 to 2 3 to 7
St. Augustinegrass Rotary 2 to 3 5 to 7
Tall Fescue Rotary 2 to 3 5 to 7
Zoysiagrass Reel 0.5 to 2 3 to 7

Status and Revision History
Published on Mar 09, 2012

Winter Grass (Poa Annua)

“One year of seeds brings seven years of weeds!” – This could not be any truer than when it comes to the fight against Winter Grass in your turf.

If you have an invasion of Winter Grass, you’ll definitely want to treat it before it germinates. If you allow it to drop its seeds, next winter it will be back, twice as badly as it was the previous year. Best plan of attack is to treat it as soon as it appears.

What is Winter Grass?

Winter Grass, or Poa Annua as it is scientifically known, is a low growing turf grass. It has soft, drooping green leaves grown in tufts with triangular shaped seed heads.

Winter Grass is widespread in Australia and spreads throughout the Winter months.

When does it appear?

Winter Grass begins germinating in the soil in May. You will start to see it emerging within your turf in late May and June and continue to spread throughout the Winter months.

How do I get rid of it?

Winter Grass can be removed very easily by hand as it doesn’t have particularly deep roots and it doesn’t have any runners, growing in simple clumps. Removing it by hand can be somewhat tedious so fortunately there are specifically targeted herbicide controls you can use. Targeting it before it emerges during May is the key to preventing it from germinating and going to seed. A pre-emergent like Oxafert can be applied and it will target the Winter Grass before it emerges from the soil.

Winter Grass Killer is a selective control that will kill Winter Grass by targeting the roots, so it is extremely important to spray early in its life cycle in May before seed heads appear. Once it goes to seed, they will be present again in your turf the following year and the cycle will continue. Using a combination of a pre-emergent like Oxafert and a selective control like Winter Grass Killer at the correct time of year should ensure it is eradicated from your lawn.

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Poa Annua Weed Control – 18 Recommended Treatment Options

With each plant being able to produce 100 seeds in as little as 8 weeks, poa annua can aggressively infest your turf before you know it.

Once a few plants become established in turf or ornamental areas, poa can spread rapidly and quickly lead to severe infestations. What’s worse is that poa annua is often too much like the surrounding desired turf to remove without harming the rest of lawn.

This article focuses on how to identify poa annua, best practices for managing the weed, the lifecycle and environmental impact of the weed, and 18 recommended treatment options.

Identification:

Poa annua (annual bluegrass) is light green, with flattened stems and boat-shaped leaf tips. It’s fairly weak, has a shallow root system, and grows well in moist areas with full sun. Poa also does well in semi-shaded conditions.

In moderate temperature areas where turf is frequently irrigated, poa annua can persist all year, but it usually dies out in the summer heat. It grows to a height of 6 to 8 inches if left un-mowed and has a flowering structure is 1 to 4 inches in length.

Life Cycle & Environmental Impact:

Poa annua starts germinating in late summer or early fall, as soil temperatures fall below 70° F.

A prolific seed producer, it will continue to germinate throughout winter with several flushes. Each plant can produce 100 seeds in as few as 8 weeks and poa can survive mowing heights of less than 1″ and still reseed days after mowing.

In winter, poa annua is more competitive than many turfgrass species and severe infestations can develop as seeds are spread by mowing, foot traffic, birds, and cultivation. In the cool season, it grows faster than warm-season turf, which can give the lawn an andulating or irregular surface in as little as 2 days after mowing.

Best Practices for Managing Poa Annua

Applying a pre-emergent herbicide is the most effective way to control poa annua and many other annual weeds. Pre-emergent creates a barrier BELOW the surface so sprouting seeds cannot push their way up.

Pre-emergent must be applied over an ENTIRE AREA to prevent seeds from germinating and herbicide MUST be applied BEFORE poa annua germinates to be effective. In many regions, the rule of thumb is to apply pre-emergent by September 15th, but time your application just prior to fall rains and when soil temperatures drop below 70º F.

Remember, pre-emergent does NOT control existing weeds and hand-weeding of poa is futile. New flushes of seedlings will only germinate after older ones are removed.
Selective post-emergent control is difficult – poa annua is too much LIKE the surrounding desired turf to remove without harming the rest of the lawn. Besides, there are more seeds just waiting to germinate, so post-emergent control would be constant.

In addition to properly using pre-emergent, there are a number of cultural practices that can help you avoid infestations:

  • Do not over-fertilize; Phosphorus encourages seedling development.
  • Do not overwater, especially in shady areas.
  • Maintain healthy plants & overseed open spots, as dense plantings make establishment of seedlings difficult.
  • Clean equipment before moving from infested to weed-free areas.
  • Reduce soil compaction.

18 Recommended Treatment Options

Sprayable Formulations

1. PRODIAMINE 65WDG

  • Longest-lasting
  • Lowest application rates means most cost effective – A 5 lb jug treats up to 10 acres
  • Non-Staining
  • Barricade Equivalent

2. SURFLAN

  • Popular for beds
  • Not safe for cool-season turf
  • Great tank-mix with Roundup for pre+post
  • Orange in color
  • 2.5 gallon jug treats 2.5 – 5 acres

3. TIP: Tank Mix with ISOXABEN DF (Gallery)

  • Does NOT control Poa, but mixed w/ Surflan or Prodiamine, it will also prevent a large list of broadleaf weeds
  • 1 lb jar treats 0.75 – 1.5 acres

Granular Formulations

1. OXADIAZON 2G

  • Popular granular formulation
  • Ronstar 2G Equivalent
  • 50 lb bag covers 11,000 – 22,000 sq ft

2. DIMENSION .25G

  • Best known for spring applications, to also control already-emerged crabgrass
  • 40 lb bag covers 9,000 – 17,000 sq ft

3. T/I 2.5G (TRIFLURALIN/ISOXABEN)

  • Controls more Grassy AND Broadleaf weeds than any other pre-emergent herbicide
  • Snapshot Equivalent
  • 50 lb bag covers 10,000 – 21,000 sq ft

PLUS FERTILIZER

TurfGro 12-4-16 w/ Barricade

  • Excellent Fall Fertilizer formula plus pre-emergent weed control in 1 Step
  • 20% Slow Release
  • 50 lb bag covers 8,000 – 12,000 sq ft

SMALL PACKAGING

  • ProDeuce – Prodiamine + Glyphosate for Pre + Post Control in 1 Step.
  • Weed Impede – Small package Surflan
  • Vegetable & Ornamental Weeder – Small Package Treflan

OTHER PRODUCT

  • Oxadiazon 50 WSB
  • Dithiopyr 40 WSB
  • Pendulum (EC & Aquacap)
  • OB 2G / XL 2G
  • Treflan
  • Casoron 4G
  • Corn Gluten/Pre-Merge (Organic)
  • TurfGro 15-3-5 w/ Dimension

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