WEEDS AND THEIR CONTROL 231 



fallow late in the fall with a "duckfoot" cultivator will 

 kill most of the winter annual and biennial weeds that 

 have started. 



When dealing with either biennials or winter annuals 

 it should be kept in mind, (1) that late fall cultivation 



Fig. 81. — Canada Thistle. 



A typical "creeping-rooted" perennial. The Sow Thistle which is some- 

 what similar in habit is more difficult to control in the Red River Valley. 



is essential whether early cultivation has been given or 

 not, and (2) that the use of biennial crops like Winter 

 rye and sweet clover which aid in the control of annual 

 weeds, only foster the development and spread of bien- 

 nial weeds. 



In some seasons some biennial weeds will germinate, 

 and like annuals, produce seed in the same year. Fall 

 cultivation will not control these. The usual cultivation 

 given to control other annual weeds will, however, take 

 care of them. 



181. The Control of Perennial Weeds. — The native 

 quack grass (Agropyron glaucum), is a typical peren- 

 nial wefed in many parts of the West. It is less difficult 



