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Annual Bluegrass Control

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

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

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

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.

Annual bluegrass (Poa annua) has a smooth leaf blade with a boat-shaped tip. Joseph M. DiTomaso, University of California - Davis, Bugwood.org

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

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

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

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. In the spring, when the seedheads become visible, mow the lawn frequently at approximately 2 inches high with a bagger on the mower to collect annual bluegrass seeds to help prevent seed spread.

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 alternate between the two different types of 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 have a different mode of action. There are two different mode of action groups of pre-emergent herbicides for residential lawns, 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 (these are called dinitroaniline herbicides), and these include benefin, dithiopyr, oryzalin, pendimethalin, prodiamine, and trifluralin. The second chemically different group (the cellulose biosynthesis inhibitor class of herbicides) includes indaziflam.

Table 1 lists granular products within these two 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 indaziflam, which cannot be used on tall fescue lawns.

It is important to note that annual bluegrass may develop resistance to the herbicides from group 1, and pre-emergence control may become reduced. Therefore, for better pre-emergence control of this grassy weed, alternate applications using products from group 1 and group 2, or at least alternate each year between the two groups of herbicides. Read the product label for how long each herbicide will last in deciding when to make a second fall application.

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, if no spring applications of pre-emergence herbicides are made for summer weed prevention. 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 the best time to apply nitrogen fertilizer on warm season lawns. Only those with 0-0-7 fertilizer (7% potassium, or some percent of only potassium) 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 Residential Lawns.

Active Ingredient Examples of Brands & Products
Group 1 Mode of Action Pre-emergence Herbicides
Benefin Lebanon Balan 2.5G (2.5%) (40#)
Andersons Crabgrass Preventer w/ 2.5% Balan Herbicide (40#)
Dithiopyr Vigoro Crabgrass & Weed Preventer 0.17% Dithiopyr (17#)
Hi-Yield Turf & Ornamental Weed & Grass Stopper containing Dimension Granules (0.125%) (35#)
Sta-Green Crab-Ex Crabgrass & Weed Preventer Granules (0.17%) (15 & 45#)
Bonide DuraTurf Crabgrass & Weed Preventer 0.27% (4# & 9.5#)
GreenLawn Crabgrass Control 0-0-7 (0.17%) (17.5#)
Harrell’s ProFertilizer 0-0-20 with 0.15% Dimension (50#)
Harrell’s ProFertilizer 0-0-7 with 0.125% Dimension (50#)
Anderson’s Professional Turf Products Dimension 0.25G (50#)
Vereens 0-0-7 w/ 0.13% Dithiopyr
Vereens 0-0-7 w/ 0.25% Dithiopyr
Lebanon Pro Fertilizer with Dimension 0.15% 0-0-7 (50#)
Nutrite 0-0-7 Fertilizer with 0.15% Dimension
TriCare GrowStar Turf Fertilizer 0-0-7 with 0.15% Dimension (50#)
Pendimethalin Scotts Halts Crabgrass & Grassy Weed Preventer (1.71%) (10#)
Harrell’s ProFertilizer 0-0-10 with 0.86% Pendimethalin (50#)
Pendulum 2G Granule Herbicide (2%) (20 & 40#)
Lesco Crabgrass Pre-emergent Plus Potash (0-0-7) (0.86%) (50#)
Prodiamine Anderson’s Professional Turf Products Fertilizer w/ Barricade Herbicide 0-0-7 (0.426%) (50#)
Anderson’s Professional Turf Products 0.48% Barricade (50#)
Howard Johnson Crabgrass Control 0-0-7 w/ 0.37% Prodiamine (50#)
Lebanon Pro Fertilizer (0-0-7) with Prodiamine (0.38%) (50#)
Pro-Mate Barricade 0.22% plus 0-0-7 (50#)
Harrell’s ProFertilizer 0-0-7 with 0.30% Barricade (50#)
Harrell’s ProFertilizer 0-0-7 with 0.45% Barricade (50#)
TriCare GrowStar Turf Fertilizer 0-0-7 with 0.37% Prodiamine (50#)
Benefin & Trifluralin Hi-Yield Crabgrass Control Granules w/ 1.33% Benefin & 0.67% Trifluralin (9#)
Anderson Turf Products Crabgrass Preventer w/ 2% Team Herbicide Granules (1.33% and 0.67%) (50#)
Lebanon Team 2G w/ 1.33% Benefin & 0.67% Trifluralin (50#)
Benefin & Oryzalin Green Light Amaze Grass & Weed Preventer w/ 1% Benefin & 1% Oryzalin (4 & 10#)
Surflan XL 2G w/ 1% Benefin & 1% Oryzalin (50#)
Group 2 Mode of Action Pre-emergence Herbicides
Indaziflam Bayer Specticle (50# bag)
Note: For best weed prevention, alternate the use of pre-emergence herbicides between those listed in the two groups to prevent herbicide resistant annual bluegrass from developing.

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

CAUTION: Atrazine can travel through soil and enter groundwater; 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.

Imazaquin (Image Kills Nutsedge) will give good post-emergence control of annual bluegrass in well-established bermudagrass, centipedegrass, zoysiagrass, and St Augustinegrass lawns. Complete control may require 2 spray applications. Best weed control is made during the fall while weeds are small. Water the spray product into the soil within 1 to 7 days for better control. Do not spray imazaquin on St Augustine lawns for winter weed control. Please read the product label for mixing, use, and other restrictions.

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 Kill-Zall Aquatic Herbicide,
  • 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 Concentrate,
  • 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, compost, bark mulch, or old hay) can be used in the garden to help suppress annual bluegrass development. Before laying the mulch, apply a layer of six to eight newspaper sheets to act as a weed barrier, and then wet the newspapers. The newspaper layer prevents weed development by blocking light to the weeds underneath and 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 deep. 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 Containing Treflan
  • 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 Ubefore planting. Avenger Weed Killer Concentrate for Organic Gardening contains d-Limonene (citrus oil) and 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. Poor control may occur 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
  • Snapshot 2.5 TG Granules (also contains isoxaben for additional broadleaf weed prevention)

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:

  • Hi-Yield Turf & Ornamental Weed & Grass Stopper containing Dimension Granules (0.125%) (35#)
  • Sta-Green Crab-Ex Crabgrass & Weed Preventer Granules (0.25%) (10#)
  • Bonide Crabgrass & Weed Preventer for Lawns & Landscape Beds Granules (0.27%) (9.5#)
  • Lebanon Pro Dimension 0.15% FG Turf & Ornamental Herbicide 0-0-7 (50#)

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 the list in the “Control in Lawns” section. As with all pesticides, read and follow all label instructions and precautions.

Original Author(s)

Millie Davenport, Director of Home and Garden Information Center, Horticulture Program Team, Clemson University

Revisions by:

Joey Williamson, PhD, HGIC Horticulture Extension Agent, Clemson University

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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