This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Native. Perennial. Propagates by seeds and by rootstocks.
Time of bloom: May to August.
Seed-time: July to October.
Range: Ontario, Manitoba, and Minnesota, to Hudson Bay, westward to British Columbia and Washington, and southward to Missouri, New Mexico, and California.
Habitat: Open prairies; fields, meadows, and pastures.
Its hooked pods make this plant very obnoxious to western wool-growers, and it is a weed that is exceedingly hard to destroy. The rootstocks are long, thick, creeping, stored with sweet juices, whence it is called Sweet-root, a translation of the Greek generic name. These thick, juicy, deep-lying roots enable it to withstand drought and recover from much cutting and grazing. Stems erect, branching, one to three feet high, usually scurfy with fine scales. Leaves long-petioled, odd-pinnate, with eleven to nineteen oblong, pointed leaflets, entire, bristle-tipped, and specked with minute scales or dots, being scurfy when young and dotted when old. Flowers densely crowded on axillary spikes, shorter than the leaves; the corolla, a little less than a half-inch long, yellowish white with narrow standard exceeding the wings and blunt keel. Pods about a half-inch long, two- to six-seeded, brown, bur-like, bristling all over with short, hooked prickles, making fast to almost anything at a touch and widely distributed by animal transportation. (Fig. 173.)
Prevent seed development and distribution by repeated cutting, beginning as soon as the first flowers wither. In order to kill the perennial rootstocks, the land requires to be kept under very thorough cultivation for three successive years, giving the weed "no chance to see daylight" throughout each growing season. Increased returns from the crops will repay extra tillage.