372 WEED FLORA OF IOWA 



Bull Thistle {Cirsiwm lanceolatum (L.) Hill). 



Description. — Branching biennial, 3-4 ft. high, tomentose, be- 

 coming dark green and villous or hirsute with age, branchlets 

 bearing large heads; leaves lanceolate, decurrent on the stem with 

 prickly wings deeply pinnatifid, the lobes with rigid prickly points, 

 upper face roughened with short hairs, lower face with a cottony 

 tomentum ; heads l%-2 in. high ; bracts of the involucre lanceolate, 

 rigid when young, more flexible with age, long-attenuated, prick- 

 ly, pointed, spreading tips, wholly arachnoid; flower hermaphro- 

 dite ; tube of the corolla 10 lines long ; anther tips acute, filaments 

 pubescent; aehenes smooth, 1% in. long; pappus of numerous 

 plumose bristles. 



Disiribution. — Bull thistle is native and indigenous to Europe. 

 It has long been an inhabitant of the northern states and now ex- 

 tends across the continent. In Iowa it is abundant in every county, 

 frequently found in fields and particularly in pastures and wood- 

 lots. 



Extermination. — This weed should be treated like all other bien- 

 nials. The most important point is to prevent the seeds from 

 forming. For this purpose the plant should be cut off in early 

 spring below the surface of the ground. The seeds germinate in 

 the spring and during the first season produce a flattened mass of 

 leaves. The second season, a flowering stem shoots up rapidly; 

 early in August the flowers begin to appear and these are continued 

 tiU frost. 



The only method of treating is to cut down and remove aU the 

 "roots" as far as it is possible to do so. If this is done frequent- 

 ly and thoroughly the weed can be exterminated. If the patch is 

 a small one, cutting off the parts as soon as they appear above the 

 ground, several times during the season, will certainly destroy 

 this thistle. In larger patches, plow the ground, harrow and re- 

 move the thistle, either burn the material, or put into compost 

 heaps. This should be done five or six times during the season or 

 as often as occasion may require. 



