260 DRY FARMING 



by no means free from their visitations. When any 

 species is found to be increasing the methods of con- 

 trol may take any one or more of three forms : first, the 

 prevention of its reproduction or its spread; second, its 

 destruction by poisoning if it is a "biting" insect; and 

 third, its destruction by chemicals that kill by contact 

 if it belongs to the "sucking" insects. In some cases 

 none of these plans of attack are successful and other 

 means of destruction are necessary. The common insect 

 pests of the West and their control are very ably and 

 plainly discussed by Mr. Griddle in Chapter XIV of 

 "Crop Production in Western Canada", and by other 

 entomologists in bulletins that may be secured free of 

 charge from the Dominion Department of Agriculture at 

 Ottawa or from any of the Provincial Departments. 



211. Plant Diseases. The most common diseases affect- 

 ing grain crops in Western Canada are smut and rust. 

 Flax wilt and certain fungous, bacterial and physio- 

 logical diseases of potatoes and other crops also take an 

 annual toll from the farmer's profit. Rust cannot be 

 controlled but its ravages may be lessened by the use of 

 rust resistant varieties as well as by all those cultural 

 practices that result in earlier maturity. The eradica- 

 tion of secondary hosts of the plant such as the barberry 

 and buckthorn lessens the probability of the appearance 

 of the disease. The grain smuts, except the loose smuts 

 of wheat and barley, can be lessened or entirely pre- 

 vented by the formalin treatment of the seed. The loose 

 smuts referred to can be controlled by the hot water 

 treatment of the seed. The physiological diseases can be 

 largely prevented by the choice of suitable varieties and 

 the use of healthy seed. The bacterial and fungous dis- 

 eases can be controlled only by the use of disease-free 



