Cenchrus spinifex (Sandbur weed)

Cenchrus spinifex is a perennial grass 13-76 cm tall. It reproduces by seeds. The stems may be erect or growing along the ground. 

It can be easily identified by its flat linear leaves and a seedhead that consists of numerous sharp bristles that attach to people’s clothing and animal fur. 

Sandbur Weed Classification

  • Domain: Eukaryota
  • Kingdom: Plantae
  • Phylum: Tracheophyta
  • Subphylum: Angiospermae
  • Class: Monocotyledonae
  • Order: Poales
  • Family: Poaceae
  • Genus: Cenchrus
  • Species: Cenchrus spinifex
  • Common Names: Stickerbur, Stickerweed, Common sandbur, and Coastal sandbur. 

Nativity and Distribution

Sandbur weed is native to the Southern United States and Central and South America. It is also found in:

  • Other parts of North America
  • Europe
  • South Africa
  • Philippines

Physical Characteristics

Sandbur weed has flat linear leaves and burs with sharp spines
Sandbur weed has flat linear leaves and burs with sharp spines. Image: inaturalist/johnmcintyre
  • Leaves: Linear, flat leaves with prominent veins
  • Fruits: 5-10mm long burs with numerous sharp spines
  • Stems: Erect or slightly arching culms
  • Flowers: Yellowish-green inflorescence attached to terminal panicles
  • Roots: Shallow fibrous root system

Cenchrus spinifex is a perennial grass that can grow erect (up to 76 cm tall) or close to the ground.

It is easily recognizable by its spiky seedhead that consists of 8-40 bristles about 5-10mm long that embed themselves in people’s clothing and shoes and animal fur. 

Stems are round and hollow, slightly glabrous, with distinct nodes, and typically green with a purplish hue.

The leaves are flat, alternate, bluish-green, about 1-7mm wide and 2-20 cm long with prominent veins. They are generally glossy on the upper surface and coarse on the underneath.

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The leaf sheath is enclosed around the stem with overlapping margins. At the point of divergence between the leaf sheath and leaf blade is a small hairy ligule 0.5-1.4mm long. 

The flowers are grouped in spikelets typically in a compound raceme. The elongated spikelets can contain one to several florets.

Each spikelet is surrounded by a round or oval bur enclosed in several prominent bristles. Flowering occurs in late summer to early fall, although this can vary depending on the climate.

Each bur contains 1-3 seeds. The seed is ovoid and flattened on one side, about 1-2mm wide and 2.5mm long and covered by a tuft of bristles at the top.

Reproduction, Dispersal, and Life Cycle

  • Life Cycle: Perennial
  • Seeds: Each plant can produce up to 1,000 seeds
  • Climate: Grows well in tropical and subtropical areas
  • Dispersal: Animals, contaminated clothing and equipment, and water

Cenchrus spinifex behaves as a perennial weed. One isolated plant can produce up to 1,000 seeds which are highly viable. 

The seeds are enclosed in burs that attach to the fur of animals, clothes and shoes of humans, and agricultural equipment for easy dispersing to new locations. They can also float and disperse along streams and irrigation canals or in contaminated produce such as hay. 

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Seeds can germinate up to a depth of 4 inches below the soil surface. Seeds at greater depths can remain viable for at least 5 years. Scarification highly encourages seed germination.

Similar Plants

  • Cenchrus longispinus
  • Cenchrus echinatus
  • Cenchrus tribuloides
  • Cenchrus incertus
  • Cenchrus biflorus

Uses

  1. Early growth is used as forage for livestock.
  2. It is used in stabilizing sandy soils and preventing soil erosion.
  3. The grass is used in restoring dune ecosystems.
  4. The plant is used as a traditional medicine to treat inflammation.

Impact on Farms and Environment

Sandbur weed is commonly found on bare sand grounds, pasture lands, farms, and lawns
Sandbur weed is commonly found on bare sand grounds, pasture lands, farms, and lawns. Image: kew.org

C. spinifex effectively stabilizes sandy soils and can prevent erosion in susceptible ecosystems. However, it is mostly considered invasive and can be found on bare sand grounds, pastures, cultivated fields, roadsides, and lawns.

It can outcompete native plants and alter local ecosystems. Due to its strong adaptability, the weed has been shown to change soil composition in sandy grass ecosystems, altering processes like soil nitrogen cycling. 

In farmlands, the weed tends to emerge with spring grains, reducing crop yield. Large weed invasions may also reduce farming acreage, causing more economic losses for farmers. 

The Sandbur weed’s stiff burs can pose a problem for grazing livestock, especially if ingested as they can cause mouth injuries. Additionally, the spiny burs can attach to their fur, causing distress. 

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The sharp burs are also a nuisance to humans and can cause scratches, skin irritation, and severe discomfort. For pets, it may require time and patience to remove the burs while minimizing animal distress.

Control

  • Mechanical control: Mowing and tillage 
  • Cultural control: Crop competition
  • Chemical control: Herbicides like Prowl H2O and glyphosate

Effective sandbur weed control depends on the region and timing of emergence. Some recommended control strategies may therefore produce contrasting results based on these conditions. 

Repeated mowing as the plant is in bloom can prevent seed setting and further spread. However, mowing alone will not eradicate the weed and may require other strategies like herbicide applications for notable results. 

Tillage is far more effective for established infestations. Ensure it’s done deeper than 4 inches of soil. Care should also be taken to avoid dispersing broken plant fragments to areas where it is not wanted. Cleaning of tools, machinery, and vehicles is highly recommended.

Cultural practices such as crop rotation and cover cropping can also help outcompete Cenchrus spinifex. Planting native grasses and maintaining well-managed pastures can also suppress the growth of sandbur weed. 

Pre-emergent applications of pre-emergent herbicides like Prowl H2O can be used to prevent new seedling flushes. Post-emergent herbicides containing glyphosate, metsulfuron, or a combination of metsulfuron and nicosulfuron are more effective for established pasture infestations.

Make sure to read the herbicide label and follow all the instructions for the best results.