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: July to September. Seed-time: September to November.
Range: The Plains region west of the Missouri River, to Wyoming, Colorado, and New Mexico.
Habitat: Dry soil; prairies; meadows and pastures, cultivated fields, waste places.
A near relative of the Common Ragweed, but much more pernicious because of its creeping rootstocks. Stems twelve to eighteen inches tall, much branched, and spreading, hoary with white hairs. Leaves alternate, smooth and green above but densely white-woolly beneath, coarsely toothed, long and bipinnate, the lobes narrow and very irregular, separated by narrow, winged segments, the petiole similarly winged. Flowers of two kinds, the sterile ones in narrow terminal racemes, the heads, about one-sixth of an inch long, on very short pedicels; the fertile heads in the axils below, singly or in small clusters; the involucre forms a tiny bur, about a sixth of an inch long, softly hairy, and bearing several small, sharp prickles. These burs are often distributed in the wool of sheep, and the weed is a most vexatious one to owners of flocks. (Fig. 320.)
Fig. 320. - White-leaved Franseria (Franseria discolor).
Like all weeds that keep a reserve supply of food in underground storage, these are very hard to kill. They must be cut close to the ground in early summer, while in their first bloom, and again in September, in order to make certain that no seed shall be matured. If persistently deprived of the sustenance supplied by leaf-growth the rootstocks must finally be starved to death. Large areas are best subdued by deep plowing and exposure of rootstocks in hot weather as recommended for Perennial Ragweed.