This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Introduced. Annual. Propagates by seeds. Time of bloom: July to September. Seed-time: August to October. Range: Locally in many parts of the country; most common in Quebec, western New York, and Virginia. Habitat: Fields, roadsides, and waste places.
In Europe this plant is a pest of grain fields. In this country it is much cultivated in flower gardens for its beauty, but has escaped in many localities and, if neglected, may become troublesome.
Stem one to two feet tall, very slender, branched and leafy and softly woolly all over, giving the foliage a grayish green tint; when old it becomes very hard and woody, whence its name of Hurtsickle. Leaves alternate, three to six inches long, those on the upper part of the plant linear and entire, those on the lower part often toothed or pinnatifid. Flower-heads about an inch and a half broad, solitary on long, slender peduncles, usually blue, but may be violet, pink, or white; florets all tubular, those in the center small and slender, perfect, and fertile, those of the outer row much longer, funnel-shaped, showy, and spreading, with deeply notched edges, pistillate but sterile; involucre ovoid, its bracts imbricated in about four unequal series, of a greenish straw-color with darker tips and margins, or fringed with chaffy teeth. Achenes four-sided, somewhat flattened, and tipped with a pappus of rough, rusty brown hairs of unequal length. These seeds have a vitality of several years as shown by the recurrence of seedlings on ground where the plants have been cultivated.
Prevent seed development by cutting or pulling while in early bloom. In this country the weed is seldom abundant in grain fields, but where it does appear many of the seedlings may be raked out with a weeding harrow, without injury to the crop, at the time when the first lower, pinnatifid leaves have grown.