ERADICATION OF WEEDS 



507 



700. spraying. The use of chemicals in destroying weeds 

 in grain fields, and to a lesser extent in meadows, pastures, 

 and lawns, has come into prominence in recent years. If 

 appUed while the plants are young, the chemical spray is 

 effective in killing practically all broad-leaved plants, while 

 it does little injury to the grains and grasses. A single 



Figure. 166. — The result of spraying grain fields with iron sulphate. The portion 

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

 a solid mass of mustard. 



appHcation will kill many annual weeds and young plants 

 of the biennials and perennials, but several applications must 

 be made to kill the older perennials, as only the top growth 

 will be destroyed by the earlier sprayings. The most com- 

 mon chemical which is used is iron sulphate, at the rate of 

 100 pounds to 50 gallons of water. About 50 gallons of the 

 solution are required to spray an acre. The weeds which 

 can be successfully treated with this spray include wild 

 mustard, Frenchweed, peppergrass, shepherd's purse, rag- 

 weed, kinghead, and marsh elder. It is less effective on 



