19 BULL THISTLE (SPEAR THISTLE) PEST STATUS of WEED Nature Of
In: Van Driesche, R., et al., 2002, Biological Control of Invasive Plants in the Eastern United States, USDA Forest Service Publication FHTET-2002-04, 413 p. 19 BULL THISTLE (SPEAR THISTLE) L.-T. Kok1 and A. Gassmann2 1Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0319, USA; 2CABI Bioscience Centre Switzerland, Delémont, Switzerland trast to those of Canada thistle. Leaves are covered PEST STATUS OF WEED with coarse hairs on the upper surface of the leaf Bull thistle, Cirsium vulgare (Savi) Tenore, is an in- blade, and are woolly below. Long spines extend from vasive thistle from Eurasia, found throughout the the leaf blade at the midrib and at each lobe. The leaf United States and in Canada from Newfoundland to bases extend downward on the stem forming long British Columbia. It is capable of invading fields, pas- wings. tures, wastelands and along roadsides, but will not Biology survive in cultivated fields. Bull thistle is a biennial species that reproduces by Nature of Damage seed. The root system consists of several primary Economic damage. Bull thistle occurs in overgrazed roots each with several smaller lateral roots. It does pastures, where heavy infestations can exclude live- not reproduce by vegetative means. Bull thistle is erect stock from infested areas. It also is common along and bushy in appearance, up to 2 m high, and has roadside and vacant fields. many spreading branches (Fig. 1). Stems are erect, Ecological damage. Although bull thistle is a stout, often branched, and hairy. Leaves are green on problem predominantly in disturbed areas, it also can the upper side, with woolly gray hairs on the under- be found in natural areas.
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