48 EXPERIMENT STATION. [Jan. 



CONTROL OF CERTAIN GREENHOUSE 



DISEASES. 



BY G. K. STONE, 



One occasionally finds growers of greenhouse crops spraying 

 for mildews and other diseases, and even contributors to the 

 florists' journals sometimes recommend such treatment, perhaps 

 because they know of no other. One at least of the objections 

 to the practice of extensive spraying is that it is too likely to 

 be considered a universal remedy or panacea for all the diseases 

 plants are heir to. Any one attempting to control the diseases of 

 greenhouse crops by spraying is wasting his time, and has much 

 to learn concerning the fundamental principles of pathology. 

 The most skilled florists and market gardeners discovered the 

 true cause of disease many years ago, not from any particular 

 experiments, but from intelligent reasoning out of the problem. 



No one can long grow crops under glass before realizing that 

 environment is a factor very largely under his control. He also 

 discovers that many, if not all, of the blights with which he has 

 to contend are caused by conditions of environment, and that if 

 these conditions are modified properly the blights are checked. 

 Considerable skill is required to manage the greenhouse in such 

 a way that blights may be controlled, but it has been accom- 

 plished very successfully in many cases. In others, they are 

 controlled to such an extent that only a minimum amount of 

 damage occurs. 



The important factors to which the grower of greenhouse 

 crops must pay attention are heat, light, moisture, circulation 

 of the air, and the chemical and mechanical conditions of the 

 soil, and a knowledge of their effects upon plant development 

 enables him to grow healthy plants. The influence of moisture 

 in the air is alone an important, perhaps the most important, 

 factor in controlling disease, and is very plain in the case of out- 



