394 



WEED FLORA OF IOWA 



Fig. 230-A. Distribution of Sow Thistle. 



clasping base rounded; achenes 3-nerved on each side and 

 margined, smooth. 



Distribution. — Common with the. preceding species, in waste 

 places. 



Extermination. — This annual is not difficult to exterminate by 

 giving thorough cultivation. 



Perennial Sow Thistle {Sonchus arvensis L.). 



Description. — ^A perennial with creeping root-stock, and milky 

 juice; leaves runeinate, pinnatifid and spiny toothed, heart-shaped 

 base ; flowers yellow ; peduncle and involucre bristly ; achenes ob- 

 compressed, wrinkled on the ribs. 



Distribution. — Common from Nova Scotia west to Saskatchewan, 

 North Dakota, Minnesota, occasional in Iowa to New Jersey and 

 New England. 



Extermination. — ^A most difficult weed to exterminate and should 

 be treated like the Canada thistle. Summer fallow with frequent 

 cultivation is the only successful method. Clark and Fletcher of 

 Canada, recommend the following: 



"Small patches may be eradicated by digging out the roots as 

 thoroughly as possible and destroying them. This may have to be 

 done several times during a season. Great care must be taken not 

 to distribute pieces of the rootstocks over the fields by harrows or 

 other implements. To exterminate Perennial Sow Thistle, some 

 ayst,ei!a,must, be adopted which will prevent the development of 

 leaves for a period sufficiently long to kill the roots by smothering 



