538 



FIELD CROPS 



be done. Such weeds as burdock, bull thistle, and mullein 

 may be exterminated by cutting them off below the crown 

 before they produce seed. Breaking up the meadow and 

 practicing a rotation of crops may be the only effective 

 means of eradicating some perennial weeds. The most com- 

 mon weeds of meadows are morning glory or bindweed, milk- 



Fig. 161. The result of spraying grain fields with iron sulphate. The por- 

 tion at the left has been sprayed; the unsprayed portion at the right appears to 

 be a solid mass of mustard. 



weed, dock, sheep sorrel, toadflax, ox-eye daisy, the plan- 

 tains, orange hawkweed, Canada and other thistles, and 

 quack grass. 



710. Weeds in Pastures. In pastures, the methods of 

 eradicating weeds are much the same as in meadows. Per- 

 sistent weeds may make it necessary to break up the pasture 



