172 FARM WEEDS OF CANADA 



when the rape is cut or pastured off, the field may be fall plowed 

 and put into hoed crop the next season, when special attention 

 can be given to any small patches that may appear. Buck- 

 wheat it> sometimes used instead of rape for a smothering crop. 



In the Prairie Provinces Perennial Sow Thistle can be 

 combatted most effectively by a bare summer-fallow, which 

 should be plowed early and cultivated throughout the season 

 as often as is necessary to keep down all leaf growth. When 

 a field is badly infested it may be necessary to plow again in the 

 fall, give thorough surface cultivation until late the following 

 spring, and sow with oats or barley to be cut green for feed. 

 Too much emphasis can not be placed on thorough cultivation, 

 for if this is not given a summer-fallow will merely enable the 

 pest to get a stronger hold. 



ANNUAL SOW THISTLE (Smchwt oleraceus L.) 



Other English names: Hare's Lettuce, Cole wort or Thistle 

 Milkweed, Milk Thistle, Milky Tassel, Swinies, Common Sow 

 Thistle. 



Introduced from Europe. Annual, roots fibrous. Stem 

 nearly simple, 1 to 4 feet high. Leaves deeply cut and toothed 

 with soft spiny teeth; the basal ones pinnatifid, terminated by 

 a large lobe, clasping the stem by their heart-shaped base, ending 

 in sharp points. The flower is pale yellow, about 1/2 to 1 inch 

 in diameter. The scaly bracts surrounding the flower-heads 

 are downy only when young, later becoming hairless. 



The seed (Plate 76, fig. 95) is somewhat similar to that of 

 Perennial Sow Thistle but a little shorter, flattened, pointed 

 at the basal end. The longitudinal ridges are wider apart, 

 much finer, and the whole surface of the seed, the ridges as well 

 as the interspaces, is finely wrinkled transversely. Pappus 

 falls off easily. 



Time of flowering: May to October; seeds ripe by July. 

 Propagation: By seeds, which are distributed by the wind. 



