CEREAL PESTS WEEDS 459 



surviving shoots should be destroyed by early spring cul- 

 tivation, and the land sown with oats or barley. This 

 process, repeated, will be so effective that any remaining 

 plants can be given special attention. 



Shaving the soil near the surface as often as the green 

 shoots appear is recommended, which method is expen- 

 sive, but if persistently followed is likely to be effective. 

 A tool similar to a broad scraper without a back may be 

 used. Hogs confined on garlic patches will root out and 

 destroy many bulbs. Crop rotations may be so arranged 

 as to have good effect (Dewey, 1897). 



Wild garlic bulblets mature just about when winter 

 wheat and rye are harvested, and are gathered with the 

 grain. They are so nearly the same size as wheat kernels 

 that it is impossible to separate them by screening. How- 

 ever, Duvel (1906) has described a method of drying and 

 then cleaning whereby the percentage of garlic in wheat 

 may be reduced from over 2 per cent to -^ per cent. 



504. Canada thistle (Cirsium arvcnse, Scop.) occurs 

 almost throughout the United States, but is common in 

 the area from the Atlantic Coast to the meridian of 98 

 and south to the Ohio River, and also in the northwestern 

 coast district. It is abundant in eastern Canada, Mani- 

 toba, and British Columbia, and spreading rapidly in Sas- 

 katchewan and Alberta. It is found frequently in grain 

 fields, where it crowds out the cereal plants, and the seeds 

 occur sometimes in the grain. 



The Canada thistle grows from 1 to 3 feet high, and possesses 

 deep running horizontal roots (Fig. 144). Leaves variable in shape, 

 deeply pinnatifid, waved and crested, very prickly in some plants 

 and less so in others, somewhat downy underneath; flower heads 

 numerous, in a large loose corymb at the top of the stem ; flowers 

 varying in color from pale purple to pink and white; plants dioe- 



