Field Sandbur

Common Sandbur

Cenchrus spinifex

Field sandbur
Field sandbur. Photo courtesy of Dick Culbert. Licensed under CC BY 2.0.
Considered to be a noxious weed in some states, field sandbur is an annual grass known for its sharp, spiny seed pods. It grows best in dry, sandy soils and can reach heights of up to 2 feet.
Field sandbur usually germinate when soil temperature reaches about 52 degrees F and continue to do so throughout the summer and into early Fall. They often grow in a "mat" shape as they mature.
The field sandbur has several stems that tend to grow horizontal at first, producing roots at the first nodes. This causes the "mat" shape. Root systems of these plants are quite shallow, and the foliage remains fairly low to the ground. Leaf blades are flat, twisted or folded and anywhere from 2 to 5 inches long.
Typical shape of a sandbur species
Mat-like growth, typical of a sandbur species. Photo courtesy of Howard F. Schwartz. Licensed under CC BY 3.0.
Flowers of the field sandbur are often partially closed in by the leaf sheath and are arranged in spikes up to 4 inches long. Each spike contains between 3 and 15 loosely-arranged burs, but it's possible for it to have 20 to 30 more compact burs. The burs themselves are spiny and yellowish with up to 15 flat, rigid spines. Each bur contains 2 seeds. Field sandbur plants can produce up to 1,000 seeds in one year.
Seedhead of a sandbur plant
Seedhead of a sandbur plant. Photo courtesy of Forest and Kim Starr. Licensed under CC BY 3.0.
Field sandbur can be an especially large problem in turfgrass and throughout the Southern Great Plains of the US. They tend to compete heavily with local plants for surface moisture and space. The sharp burs that are released in the fall can be very injurious for skin and clothing when contacted directly.
The best way to prevent germination of field sandbur is to ensure a dense stand of healthy plants that are more desireable. Less frequent and higher-volume irrigation helps control the weed, as the moisture penetrates deeper into the soil where the sandbur's roots cannot reach and leaves the surface fairly dry in-between watering. Dormant-season tilling is helpful in controlling the weed as well. Some producers prefer burning as a method of suppression, but it requires a lot of available fuel in order to kill the seeds in the ground.
After a light burn, bared crop fields will allow heavy germination of field sandbur in the case of an infestation. One can then follow this emergence with a heavy dose of postemergence herbicide like glyphosate, nicosulfuron-metsulfuron methyl mix, or imazapic. An effective preemergence herbicide (mostly used in bermudagrass pastures or hayfields) is pendimethalin. Please contact your local weed specialist to learn what is most effective in your area and how to use it best. Always read and follow all label instructions.