Bahiagrass

Prepared by Millie Davenport, HGIC Horticulture Extension Agent, Clemson University (New 10/08. Pesticides updated 10/10.)

HGIC 2316

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Bahiagrass (Paspalum notatum), also known as highwaygrass, is an aggressive, warm-season perennial grass. Bahiagrass has a mat-forming habit with a light green color, coarse texture and open canopy. It is native to South America and was introduced into the U.S. in Florida as a forage grass around 1913.

Bahiagrass habit with seed heads.
Bahiagrass habit with seed heads.
Ted Bodner, Southern Weed Science Society, Bugwood.org

Bahiagrass is easily identified by its distinctive “Y-shaped” seed head. It tolerates a wide range of soil conditions and spreads by seeds and rhizomes (a horizontal, modified stem found at or just below ground level). Bahiagrass growth is favored by drought, so it is an indicator plant for droughty soil conditions. The aggressive nature and drought tolerance of bahiagrass make it ideal for erosion control along roadsides and highway rights of way. However, its aggressive nature also makes it difficult to control as a weed in the landscape.

Y-shaped seed heads of Bahiagrass
Y-shaped seed heads of Bahiagrass.
Bert McCarty, Clemson University

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

Control in Lawns

Maintaining the health and density of your lawn is the best method for preventing a weed problem. Proper mowing height, irrigation and fertilization of the turfgrass will be the best defense 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 bahiagrass becomes a problem in a turf area, it can be dug up or an herbicide may be used. If an herbicide treatment is chosen, treatments should be timed appropriately for optimum effectiveness.  Atrazine (Hi-Yield Atrazine, Southern Ag Atrazine, Image for St. Augustinegrass & Centipedegrass with Atrazine, and Spectracide Weed Stop for Lawns Concentrate for St. Augustine & Centipede Lawns) a pre-emergent herbicide that may give fair control of bahiagrass seed but is only safe to use on centipedegrass and St. Augustinegrass. For maximum effectiveness apply atrazine when air temperatures reach 65-70 °F for four consecutive days.

Since bahiagrass is a perennial weed that also reproduces by rhizomes, post-emergent herbicides will also be necessary for improved control. Post-emergent herbicide applications should start in May, when bahiagrass is small and starting to actively grow. See table for safe herbicides according to turf species.

Non-selective herbicides such as glyphosate can be used for spot treatments, however, nearby desirable grasses and plants can be severely injured or killed. Multiple applications of glyphosate will be required to control bahiagrass. Examples of glyphosate products are Roundup Original, Eraser Systemic Weed & Grass Killer, Quick Kill Grass & Weed Killer, Bonide Kleenup Grass & Weed Killer, Hi-Yield Super Concentrate Killzall Weed & Grass, Maxide Super Concentrate 41% Weed & Grass Killer and Southern States Grass & Weed Killer Concentrate. If it is not practical to prevent glyphosate from getting on desired grasses, a selective herbicide should be used. The following information is a guideline for choosing a selective herbicide according to turfgrass type.

For centipedegrass lawns, the use of sethoxydim (Vantage Grass Killer) will suppress bahiagrass. Sethoxydim should be used no sooner than 3 weeks after centipedegrass spring green-up. To more effectively treat the bahiagrass, do not mow 7 days before or after treating with sethoxydim. Reapply sethoxydim 3 weeks after initial application to suppress bahiagrass growth and seed head development.

Imazaquin (Image Nutsedge Killer Herbicide) is a post-emergence herbicide that will aid in the control of and reduce competition from bahiagrass. It may be applied to established bermudagrass, Zoysiagrass, centipedegrass and St, Augustinegrass, but do not apply to tall fescue. Do not apply imazaquin to St. Augustinegrass for other weed control during the winter. Do not apply imazaquin just prior to or during spring transition (green-up of the lawn). Do not use imazaquin in vegetable gardens and do use the grass clippings from treated lawns as mulch in landscape beds or around vegetables, fruit trees or small fruit plants.

Metsulfuron (such as in Manor and Blade) is a product packaged for landscape professionals. Due to the cost of this selective herbicide it may be more economical to hire a landscape professional for weed treatment. Metsulfuron can be used on bermudagrass, St. Augustinegrass, centipedegrass, and zoysiagrass. A non-ionic surfactant (such as Southern Ag Surfactant for Herbicides) is required at 2 teaspoons per gallon of spray mix for best control. Do not overseed for 8 weeks or plant woody ornamentals in treated areas for one year after application of metsulfuron. Do not apply metsulfuron herbicides within two times the width of the drip line of desirable hardwood trees.

Turf Tolerance to Post-emergence Herbicides for Bahiagrass Control
Herbicide Bermudagrass Centipedegrass St. Augustinegrass Tall Fescue Zoysiagrass
S= Safe at labeled rates.
I= Intermediate safety, use at reduced rates.
NR= Not Registered for use on and/or damages this turfgrass.
sethoxydim NR S NR NR NR
imazaquin S-I I I NR S
metsulfuron S S S-I NR S
MSMA S-I NR NR I S-I

Bahiagrass growing in bermudagrass, zoysiagrass and tall fescue lawns can be spot treated with MSMA (such as in Bonide MSMA Crabgrass Killer, Ferti-lome Improved Bermuda Grass Weeder, Green Light MSMA Crabgrass Killer 2 and Hi-Yield 529 MSMA Weed Killer) for bahiagrass control. However, MSMA products are no longer being manufactured with labels for use on residential lawns. If found, existing stock of these products with labels which allows for use on residential lawns may still be purchased and used according to the label.

Good control can be achieved with spot applications of MSMA applied three times at 7 to 10 day intervals. The addition of a non-ionic surfactant (such as Southern Ag Surfactant for Herbicides at 2 teaspoons per gallon of spray mix) is necessary if formulation does not contain it. Turf may become temporarily discolored after application. NOTE: ‘Meyer’ zoysia is more tolerant of MSMA than ‘Matrella’ and ‘Emerald’.

Once bahiagrass weeds have been eliminated in areas of the turf, bare spots will be left behind. To prevent the invasion of new weeds in these bare spots it is best to fill them with plugs or sprigs of the desired turfgrass.

Control in Vegetable Gardens

It is best to attempt to treat weeds before tilling the soil for a vegetable garden. Tilling can break up and spread weed seed and perennial grass rhizomes throughout the garden plot. Some methods used to remove weeds in the vegetable garden include: hand pulling, mulch and post-emergent herbicides.

Hand pulling bahiagrass 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 of the bahiagrass can be removed easily from the soil.

Organic mulch (such as pine needles, ground leaves, compost, old hay or grass clippings) can be used in the garden to help suppress bahiagrass development. Before laying the mulch apply a layer of 6 to 8 wet newspaper sheets to act as a weed barrier. The newspaper layer will prevent weed development by blocking light to the weeds underneath, preventing their growth. Best of all, the newspaper should decompose before next 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 the vegetable garden see HGIC 1253, Controlling Weeds by Cultivating & Mulching.

Lastly, a post-emergent herbicide can be used to treat the garden plot before planting. Glyphosate  can be applied to the garden plot 3 or more days prior to planting. Examples of glyphosate products are Roundup Original, Eraser Systemic Weed & Grass Killer, Quick Kill Grass & Weed Killer, Bonide Kleenup Grass & Weed Killer, Hi-Yield Super Concentrate Killzall Weed & Grass, Maxide Super Concentrate 41% Weed & Grass Killer and Southern States Grass & Weed Killer Concentrate. Glyphosate is most effective when weeds are actively growing, so do not apply during extreme heat, cold or drought conditions. Multiple applications of a 1.5 to 2.0% glyphosate solution may be necessary for control of perennial weeds like bahiagrass.

Control in Landscape Beds

In landscape beds bahiagrass can be hand dug or controlled with an herbicide. As mentioned previously, it is best to prevent the invasion of bahiagrass by maintaining ideal growing conditions and using a 3-inch mulch layer to block weed development. Bahiagrass is a perennial weed that can emerge from both seeds and rhizomes. Once bahiagrass has made its way into the landscape bed an herbicide may be necessary if hand pulling is not practical.

Glyphosate can be used for spot treatments around ornamental plants. Examples of glyphosate products are Roundup Original, Eraser Systemic Weed & Grass Killer, Quick Kill Grass & Weed Killer, Bonide Kleenup Grass & Weed Killer, Hi-Yield Super Concentrate Killzall Weed & Grass, Maxide Super Concentrate 41% Weed & Grass Killer and Southern States Grass & Weed Killer Concentrate. Glyphosate is a non-selective herbicide that should be used with caution. Do not allow glyphosate spray mist to contact ornamental foliage or stems as severe injury will occur. A cardboard shield may be used to prevent glyphosate spray from drifting to nearby ornamentals.

Sethoxydim (such as in Vantage Grass Killer, Hi-Yield Postemergence Grass Herbicide, Bonide Grass Beater Over-the-Top Grass Killer Concentrate, and Ferti-lome Over-the-Top II Grass Killer Concentrate) is a selective herbicide that can be applied safely in landscape beds containing certain landscape plants; see product label for a listing of tolerant plant materials. Once sethoxydim is determined to be safe to use around ornamental plants, a 2.5% solution should be applied before bahiagrass reaches 4 inches tall.

Glyphosate and sethoxydim are both more effective when weeds are actively growing and should not be applied under drought conditions. As with all pesticides, read and follow all label instructions and precautions.

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This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.