PRINCIPLES OF WEED CONTROL 



349 



spread by means of tillage implements which merely transfer them 

 from place to place. The more quack grass is cultivated the more 

 it may be spread. 



Principles of Weed Control.— It is important to study the life of 

 a weed if you wish to eradicate it. Learn its habits and then you 

 can control it. It is easy to detect a weed that stores nourishment 



Fig 



246. — Base of Johnson grass showing the joints on the underground stems or "roots,' 1 

 from which numerous grass stems arise. This makes it a serious weed. 



in the underground parts. One can find the mass of stored material 

 by pulling it up. Then you know it is not an annual. 



If weeds have abundant rootstocks, as quack grass and Canada 

 thistle, you cannot hope to find all of these numerous growths 

 ramifying the soil. The control methods recommended in each 

 case are to smother the plant. 



Remember that plants cannot live if they do not have leaves 

 exposed to the air during a part of the growing season. In chicken 

 yards and pig pens where the leaves are continually eaten off the 



