This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Introduced. Perennial. Propagates by seeds.
Time of bloom: July to September.
Seed-time: August to October.
Range: Nova Scotia and Ontario to Minnesota, southward to Georgia and Missouri. Habitat: Roadsides, farmyards, and waste places.
An escape from garden cultivation. The oil distilled from the plant, mixed with that of Fleabane and Pennyroyal and diluted with alcohol, make a "mosquito dope" useful to hunters and fishermen and others who must work where mosquitoes are troublesome. Collectors receive three to five cents a pound for the dried leaves and tops, gathered when in full bloom. (Fig. 344.)
Stem one to three feet high, rather stout, smooth, usually unbranched, except at the flowering top. Leaves alternate, the lower ones sometimes a foot long, deep green, smooth, pinnatifid, the segments narrow, acute, and toothed, the petioles often with toothed margins; upper leaves smaller and less divided. Heads numerous in terminal corymbose clusters, less than a half-inch broad, yellow, the florets usually all tubular or sometimes with an outer row of imperfectly developed rays; these are pistillate, the central florets perfect, all fertile. Achenes angled or ribbed, with a five-toothed crown for pappus.
Fig. 344. - Tansy (Tanacetum vulgare).
Small areas may be grubbed out, or killed with Caustic soda or hot brine. Or the roots may be starved by successive close cutting throughout the growing season.