Tall Weed With Black Seeds

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Do you have prostrate weeds with small yellow, clover-like flowers in your garden beds or lawn? This leguminous plant from Europe and temperate Asia, commonly called black medic, is also called yellow trefoil, black clover and hop medic. Read more about this annual weed and how to deal with it in this article… WeedAlert.com features detailed color photos of over 100 weeds allowing turf professionals to search and identify weeds by name, appearance or region. Detailed information about each weed includes description, non-chemical cultural practices in how to control the weed, geographic coverage maps of where they grow and when they are prevalent in the various growing zones, as well as herbicide use and recommended control products. Bahiagrass (Paspalum notatum), also known as highwaygrass, is an aggressive, warm-season perennial grass. Bahiagrass has a mat-forming habit with a light…

Black Medic, Medicago lupulina

A dense infestation of black medic.
Black medic, Medicago lupulina, is a common, prostrate broadleaf weed that is found throughout the US and Southern Canada. Native to Europe and temperate Asia, this member of the legume family (Fabaceae) has a few other common names including yellow trefoil, black clover and hop medic. Its is most often found as a weed in in dry, sunny areas in turf and waste ground, such as along roadsides and railroads, but it can be a nuisance in gardens and fields as well. Black medic can be an indication of low soil nitrogen in lawns as it outcompetes weak grass. Black medic and white clover grow in similar sites and are often found growing together in turf. Although it is classified as a cool season summer annual, in mild winters some plants may survive to act as a perennial. It spreads easily by seed and will form large colonies if left undisturbed.
A young black medic plant.
Black medic produces a long taproot that grows deeply into most soils. Several trailing, slightly hairy stems grow out from the base. The plant grows close to the ground, spreading up to 2 feet, but does not root along the stems. Like other members of the legume family, black medic has a symbiotic relationship with Rhizobium bacteria that form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby.
A black medic seedling (L) and trifoliate leaf (R).
The tiny seedlings resemble other clovers, with elongate, dark green cotyledons and rounded first leaf. All other leaves are trifoliate. The plant’s dark green leaves are similar to clover leaves, with three oval leaftlets. Each ½-¾” long leaflet has a small spur or tooth at the tip, toothed margins, and prominent, parallel veins. The center leaflet protrudes slightly on an extended petiole. This characteristic, along with the small projecting tip at the leaflet apex and toothed margins, help to distinguish black medic from other trifoliate legumes. The leaves are produced alternately along the stems. There is a pair of stipules (small, leaflike appendages) where each petiole joins the main stem.
Black medic flower.
The small, bright yellow flowers are produced from the leaf axils. Each inflorescence is a compact, rounded to slightly elongated cluster of 10-50 tiny flowers. Flowers can be found throughout the growing season, although individual plants stop blooming once seeds are set. Honeybees and other bees visit the flowers. The fruits that form after pollination look like small kidneys arranged in clusters. The coiled seed pods turn black when ripe. Each seed pod contains a single gold or brown seed.
In lawns, black medic can be managed through good turf management practices that encourage a dense stand of turf (high mowing, proper fertilization and irrigation), making it difficult for black medic to persist. As black medic often grows where some soil compaction has occurred, such as along curbs and sidewalks, reducing compaction will also help.
Black medic fruits (L) and ripe seed pods (R).
Black medic produces viable seed under normal mowing conditions which can persist in the soil for years, so it is important to control this weed before flowering and seed set. Individual plants can be hand pulled. Even larger plants are easy to pull out, particularly after rain has softened the soil. However, for large areas or dense infestations, a broadleaf herbicide can be applied to actively growing plants during the seedling to flower growth stage. Chemical controls are best applied from late spring through early summer and again from early through mid-autumn. Read and follow label directions carefully.
– Susan Mahr, University of Wisconsin – Madison

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Tall Weed With Black Seeds

Bahiagrass, a coarse-textured warm-season perennial (C-4) which does not form a tight knitted turf. Bahiagrass has a rolled vernation, ligules which are membranous in nature with short hairs on the back of the ligule. Auricles are absent and the sheath is flattened. The leaf blades are coarse, light green in color, pointed at the tip and sometimes have hairs located near the base. The blades are typically folded near the base. Leaf blades are very fibrous and difficult to cut cleanly, causing them to fray and give turf a rough appearance. Bahiagrass has an extensive deep root system and is very drought tolerant. Bahiagrass is often identified by the distinctive “V” shape (see seedhead insert) created by the two slender spiked racemes (sometimes there are three, but not often) with two rows of oval seeds. The tall seed stalks are a problem due to their rapid growth and require constant mowing in fine turf. Bahiagrass produces seedheads from June through November. Bahiagrass reproduces from seed and from short rhizomes and stolons which are so stout they are almost woody. Since old leaf sheaths persist at the base, they tend to have a woody appearance as well. Introduced from Central and South America as a forage grass in the early 1920’s. Fine turf areas, roadsides and pastures are easily invaded by this aggressive plant. Bahiagrass is found along coastal states from southern Virginia to Texas and in California.

Weed Photos: Courtesy of Dr. Lambert McCarty . Clemson University. Clemson, SC.

Herbicide Use

Mid-summer is the optimum time for a post-emergence application of metsulfuron to control bahaigrass which has invaded bermudagrass. For renovation of areas containing bahiagrass, use a glyphosate product.

Bahiagrass

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 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.

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

Bahiagrass has distinctive “Y-shaped” seed heads.
Bert McCarty,©Clemson University

Before starting a weed control program, homeowners should realize that the 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 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.

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.

Turf Tolerance to Post-emergence Herbicides for Bahiagrass Control.

Herbicide Bermudagrass Centipedegrass St. Augustinegrass Tall Fescue Zoysiagrass
sethoxydim NR S NR NR NR
imazaquin S-I I I NR S
metsulfuron S S S-I NR S
atrazine D S S NR NR
S= Safe at labeled rates.
I= Intermediate safety, use at reduced rates. Temporary yellowing of the turfgrass may occur.
NR= Not Registered for use on and/or damages this turfgrass.
D= Dormant. However, with the mild winters of recent years, bermudagrass lawns may not become completely dormant.

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.

Glyphosate: Non-selective herbicides, such as glyphosate, can be used for spot treatments; however, desirable grasses can be severely injured or killed with contact. Multiple applications of glyphosate will be required to control bahiagrass. Examples of glyphosate products in homeowner sizes are:

  • Roundup Original
  • Martin’s Eraser Systemic Weed & Grass Killer
  • Tiger Brand Quick Kill Grass & Weed Killer
  • Ultra Kill Weed & Grass Killer Concentrate
  • Ace Concentrate Weed & Grass Killer
  • Bonide Kleen-up Grass & Weed Killer
  • Gordon’s Groundwork Concentrate 50% Super Weed & Grass Killer
  • Monterey Remuda Full Strength 41% Glyphosate
  • Hi-Yield Super Concentrate Killzall Weed & Grass Killer
  • Southern States Grass & Weed Killer Concentrate
  • Zep Enforcer Weed Defeat III
  • Eliminator Weed & Grass Killer Super Concentrate
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If it is not practical to prevent glyphosate from getting on desired grasses, then a selective herbicide should be used. The following information is a guideline for choosing a selective herbicide according to turfgrass type.

Atrazine: Atrazine is a post-emergence herbicide for bahiagrass control that also has pre-emergence activity to give fair control of bahiagrass seed. It will also give post-emergence control of many broadleaf weeds. However, it is only safe to use on centipedegrass and St. Augustinegrass lawns. For maximum effectiveness, apply atrazine when air temperatures reach 65-70 °F for four consecutive days. Examples of atrazine products in homeowner sizes are:

  • Hi-Yield Atrazine Weed Killer Concentrate
  • Southern Ag Atrazine St Augustine Weed Killer Concentrate

Sethoxydim: For centipedegrass lawns, the use of sethoxydim (BASF Segment II Herbicide) will suppress bahiagrass. Sethoxydim should be applied no sooner than 3 weeks after centipedegrass spring green-up. Wait until lawns are fully greened. For a more effective bahiagrass treatment, 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. Do not make more than two applications per growing season.

Imazaquin: Image Kills Nutsedge is a homeowner-packaged, post-emergence herbicide product 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 not use the grass clippings from treated lawns as mulch in landscape beds or around vegetables, fruit trees, or small fruit plants. A repeat application may be made for difficult to control weeds after 6 weeks.

Metsulfuron: Quali-Pro MSM Turf Herbicide, Quali-Pro Fahrenheit, and Blindside Herbicide are professional use herbicide products that will control bahiagrass, as well as many broadleaf weeds.

Metsulfuron can be used on bermudagrass, St. Augustinegrass, centipedegrass, and zoysiagrass. The Quali-Pro Fahrenheit also contains dicamba for broadleaf weed control. Blindside Herbicide also contains sulfentrazone for nutsedge control.

A non-ionic surfactant (such as Southern Ag Surfactant for Herbicides, Hi-Yield Spreader Sticker, or Bonide Turbo Spreader Sticker) is required at 2 teaspoons per gallon of spray mix for best control with the metsulfuron products above. Read the metsulfuron product label for more information. Some discoloration of turfgrass may occur after the application of metsulfuron, and increased yellowing and stunting of turfgrass may occur with the addition of the surfactant. A repeat application may be required in 4 to 6 weeks for best control of bahiagrass. Follow label directions for a reduced rate on centipedegrass.

Do not over-seed or re-sod for 8 weeks, or plant woody ornamentals in treated areas for one year after applying metsulfuron. Do not apply metsulfuron herbicides within two times the width of the drip line of desirable hardwood trees. Do not allow spray drift to contact desirable shrubs, and high temperatures at application may increase herbicide drift. Make metsulfuron applications when temperatures are below 85 °F. Allow one week between application of metsulfuron and other lawn pesticide products. Read the product label for other precautions for each turfgrass species.

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.

Cultural Control: Hand pulling bahiagrass may be a practical choice for small garden plots. If hand pulling, be sure to work when the soil is moist so that the bahiagrass roots can easily be removed 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 and prevent 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 deep. For more information on mulching the vegetable garden, see HGIC 1253, Controlling Weeds by Cultivating & Mulching.

Glyphosate: 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. 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 to control perennial weeds like bahiagrass. See product label for mixing directions. For examples of glyphosate products in homeowner sizes, please see the “Control in Lawns” section.

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Sethoxydim: Some products containing sethoxydim may be applied within the vegetable garden after planting. These will control most grass weeds, in addition to bahiagrass. However, do not apply near sweet corn. Examples of products labeled for use within vegetable gardens are:

  • Hi-Yield High Yield Postemergence Grass Herbicide
  • Bonide Grass Beater Over-the-Top Grass Killer II Concentrate
  • Ferti-lome Over-the-Top II Grass Killer Concentrate
  • Monterey Grass Getter
  • Poast Herbicide

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: A non-selective herbicide, such as glyphosate, can be used for spot treatments around ornamental plants but 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. For examples of glyphosate products in homeowner sizes, please see the list above in the “Control in Lawns” section.

Sethoxydim: Sethoxydim is a selective herbicide that can be applied safely in landscape beds containing most landscape plants but check the product label for a listing of tolerant plant materials. Sethoxydim will only control grass weeds; however, do not allow sethoxydim to contact ornamental grasses. A 2.5% solution should be applied before bahiagrass reaches 4 inches tall. Read label directions for mixing. Examples of products containing sethoxydim in homeowner sizes are:

  • Hi-Yield Grass Killer Postemergence Grass Herbicide
  • Bonide Grass Beater Over-the-Top Grass Killer II Concentrate
  • Ferti-lome Over-the-Top II Grass Killer Concentrate
  • BASF Segment II Herbicide
  • Monterey Grass Getter

Glyphosate and sethoxydim are both more effective when weeds are actively growing and will not work well for weed control under drought conditions. As with all pesticides, read and follow all label instructions and precautions.

CAUTION: Atrazine and imazaquin can travel through soil and enter groundwater; please read the label for all environmental precautions. Users are advised not to apply atrazine or imazaquin 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.

Pesticides are updated annually. Last updates were done on 7/22 by Barbara Smith.

Originally published 10/08

If this document didn’t answer your questions, please contact HGIC at [email protected] or 1-888-656-9988.

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

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.

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