This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Native. Annual. Propagates by seeds.
Time of bloom: June to August.
Seed-time: July to September.
Range: Maine and Ontario to the Dakotas, southward to Florida, Texas, and Southern California; most troublesome in the South. Habitat: Sandy soil; shores and waste places.
Usually this grass may be found growing near any place where wool has been stored and cleaned. The burs are said to be more difficult to remove from the fleeces than any others, and a tribulation they must be to the poor beasts in whose hides they rankle.
Fig. 11. - Sand-bur (Cenchrus tribuloides). X 1/4.
Culms ten inches to two feet in length, with many branches, the longer ones spreading and decumbent for part of their length, the shorter ones erect. Sheaths very loose, slightly flattened, smooth but with hairy margins, the ligule conspicuously fringed; blades two to five inches long, smooth, usually flat but sometimes involute. Racemes bearing eight to twenty clusters of two to six flowers, the clusters subtended by ovoid or globular involucres which later enclose the seeds, forming hairy burs about a quarter-inch in diameter, thickly set with stiff, sharp, finely barbed prickles, which are strong enough to penetrate shoe leather. (Fig. 11.)
Small areas about sheep-washing places should be hoe-cut, hand-pulled, or burned over before the burs ripen. A sandy pasture or meadow infested with the weed should be burned over, cultivated, and fertilized before reseeding to better growths. As a waste-land weed, a whole neighborhood should be interested in its extirpation because of its habit of making any passing animal or person its carrier to a new field.