The biology of Canadian weeds. 114. Symphyotrichum pilosum (Willd.) Nesom (Aster pilosus Willd.)

Abstract

Symphyotrichum pilosum (Willd.) Nesom, the white heath aster, is a robust, native North American, polyploid, herbaceous perennial. Until recently the species was treated as part of Aster. Its placement in the segregate genus Symphyotrichum follows the revised generic combinations proposed for North American asters. Occurring throughout eastern North America from Nova Scotia and Maine in the northeast, southward to Georgia, west ward through southern Quebec and Ontario to Wisconsin, Iowa, Kansas, and Arkansas in disturbed areas such as fallow land, roadsides, dumps, quarries, arable fields, railroad beds, and embankments, the species is troublesome in the United States but a weed of minor importance in Canada. Two varieties, var. pilosum and var. pringlei are recognized. The former, the hairy variety, is weedier than the latter, the hairless variety. The species commonly occurs in fields following the first year of abandonment and may dominate in the second, or subsequent years. Control may be achieved through the application of selected herbicides. Also, even a moderate amount of grazing by herbivores such as small rodents and rabbits is sufficient to restrict growth in the species. Mildew is chronic and widespread in natural populations but typically neither kills the plants nor prevents seed production. This contribution summarizes the known biological data for the species. Key words: Symphyotrichum pilosum, Aster pilosus, white heath aster, weed biology, var. pilosum, var. pringlei