This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Introduced. Annual or biennial. Propagates by seeds. Time of bloom: Early May to August. Seed time: July to September. Range: Quebec to Ontario and Michigan, southward to Georgia and Kansas. Habitat: Grain and clover fields, meadows, waste places.
An early immigrant from Europe, probably coming with the first seed-wheat. Once in the soil it was safe to stay, for the hard seeds retain their vitality for many years. Root red, thickish, rather deep, fringed with spreading, fibrous rootlets. Stem six to eighteen inches high, slender, branching, finely hairy. Alternate leaves a half-inch to two inches long, linear to lance-shaped, light green, entire, sessile or the lowest with short petioles, hairy on both sides. Flowers sessile or very nearly so in the upper axils; corolla cream-white, funnel-form, five-lobed, about a quarter-inch long, scarcely exceeding the hairy calyx, and having five stamens included in its tube. The spikes at first appear crowded but become distant with the succession of bloom, which is so long that ripe nutlets are dropping from the base while buds are yet developing at the top; the earlier fruits fall before the accompanying crop is ready for harvest. Nutlets about a tenth of an inch long, dull brownish gray, wrinkled, pitted, and hard as stone, whence one of the common names; they are a common impurity of poorly cleaned wheat and rye, and also of timothy and alsike clover. (Fig. 236.)
Fig. 236.-Wheat-thief (Li-thospermum ar-vense). X 1/4.
Sow clean seed. Where the appearance is new and the areas small enough to permit of hand-pulling, that operation pays because it saves the soil from befoulment. Spray infested grain fields with Iron sulfate or Copper sulfate when the first blossoms appear. Burn over stubbles for the purpose of destroying seeds on the surface. Drop winter wheat and rye from the rotation until a cultivated crop has been grown on the land for the purpose of stirring dormant seeds into growth.