THE SUNFLOWER FAMILY 165 



Occurrence: Abundant in eastern Canada, Manitoba and 

 British Columbia; rapidly spreading in Saskatchewan and 

 Alberta. 



Injury: A gross feeder and a vigorous grower, which not 

 only crowds out crops but is conspicuous evidence of negligent 

 farming. The seed is frequently found in grass and clover seeds 

 and in seed oats. 



Remedy: Being a deep-rooted perennial, Canada Thistle 

 should be plowed deep in summer, just as the flowers open; or 

 the flowering stems may be mowed down and the land plowed 

 as soon as a new growth appears. As new stems are thrown 

 up they must be cut off with a broad-shared cultivator at intervals 

 through the summer and autumn. Deep plowing late in autumn 

 has been found useful in suppressing thistles in Manitoba. 



The chief safeguard against Canada Thistle and all similar 

 deep-rooted perennials is undoubtedly a regular short rotation 

 of crops with thorough cultivation. A three-year rotation, 

 including two cuttings of early red clover for the first year, 

 followed by deep fall plowing for hoed crops with clean cultivation, 

 and a cereal crop for the third year, will suppress it. 



ALLIED SPECIES: In addition to Canada Thistle, farmers 

 sometimes complain of two other allied species. Bull Thistle or 

 Spear Thistle (Cirsium lanceolatum (L.) Hill.) is a large, coarse 

 biennial, introduced from Europe, 2 to 4 feet high, widely 

 branching, with many large, deep purple flower heads, 1 

 inches high by as much across. The seed (Plate 76, fig. 88) is 

 similar to that of Canada Thistle, but larger, about 1/6 of 

 a?n inch long, plumper in proportion to the length, generally 

 darker at the broader end, grayish brown in colour, marked 

 with faint longitudinal lines. It occurs sometimes in seed 

 grain. The treatment given for Lesser Burdock is effective 

 for this weed. 



Prairie Thistle or Western Bull Thistle (Cirsium undulatum 

 (Nutt.) Spreng.) is a native perennial with running root- 

 stocks and large, white-woolly leaves and stems; flower heads 



