94 WEEDS OF THE FARM AND GARDEN 



ployed to destroy noxious weeds, especially where iu is 

 difficult to remove them by ordinary cultivation. In the 

 summer fallow the annual weeds will spring up and soon 

 cover the ground. These weeds should be turned under 

 when green, as they will add much to the fertility of the 

 soil. In the case of perennial weeds, it may be necessary 

 to cultivate the field frequently every week, especially in 

 the case of quack grass and horse nettle. It is certain 

 that the summer fallow, with frequent cultivation, will do 

 much to destroy quack grass. 



Destruction of Weeds by Chemicals or Herbicides. 

 For many years, both in this country and in Europe, ex- 

 periments have been made with various substances look- 

 ing toward the destruction of fungi by chemical means. 

 For nearly a century, blue vitriol has been used to de- 

 stroy the spores of smut. It has been known also for 

 many years that certain chemicals, known as herbicides, 

 are valuable for the destruction of weeds. While cer- 

 tain substances, as copper sulphate, for example, are gen- 

 erally recommended for the destruction of fungi, some 

 persons hold that copper, in some of its forms, is injuri- 

 ous to vegetation. 



However this may be, it is also true that copper sul- 

 phate in various forms, chiefly in the preparation known 

 as bordeaux mixture, is one of the most valuable means 

 that the horticulturist has for combating fungous diseases. 

 It is likewise true that copper sulphate, in some of its 

 forms, when used to kill the smut spores in corn, is more 

 or less injurious to the young plantlet. The injury here 

 retards somewhat the development of the oat or wheat 

 plant, but the plant recovers completely later. 



The discovery was made in France about a dozen years 

 ago that copper sulphate destroyed charlock and 

 mustard. The discovery was accidental, but it led M. 

 Aime Girard to experiment with various materials in the 

 same line, and since then many experiments with these 



