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: June to August.
Seed-time: July to September.
Range: Manitoba to British Columbia, southward to Nebraska, New Mexico, and California. Habitat: Cultivated crops, grain fields, meadows, and waste places.
A very pernicious weed, difficult to suppress because of its extensive system of tough, woody rootstocks which send up many fruiting stalks, causing it to form dense patches, crowding and starving all other growth. It intrudes in most crops and thrives almost anywhere, but seems to have a preference for soil that is alkaline. The whole plant has a rank, unpleasant odor, causing it to be disliked by grazing animals.
Stems six inches to nearly two feet high, erect, diffusely branched and very leafy. Leaves narrowly oblong or obovate, a half-inch to two inches long, somewhat thick and fleshy, rough-hairy, three-nerved, entire and sessile; the lower ones opposite, those near the top alternate. Heads inconspicuous, solitary, axillary, and drooping, the central florets sterile; bracts of the involucre united into a five-lobed cup, surrounding the fertile pistillate florets which are usually four or five in number. Achenes ovoid, flattened, sometimes keeled on one side, varying in color from green to almost black; they have no pappus. (Fig. 316.)
Prevent all seed production by repeated close cuttings throughout the growing season. The rootstocks must be starved to death after the manner of Horse Nettle or Perennial Sow Thistle, by short rotations with cultivated crops well fertilized and so well tilled that no leaf-growth is permitted to store the weed's underground x 1/6 stems with sustenance. Alternate with such crops as clover and rye, which may be cut often for soiling or may be plowed under to furnish green manure for another well-tilled hoed crop.
Fig. 316.-Poverty Weed (Iva axillaris).