METHODS OF CONTROL 191 



previously contaminated bed. Infected 

 greenhouse soil may be rendered useful 

 and free from disease by either the steam 

 or the formaldehyde methods of steriliza- 

 tion. 



(a) Steam Sterilization. This method 

 is practical in the greenhouse (fig. 45) 

 or on seed beds only where the areas are 

 limited. Its use is possible only where 

 steam is to be had from a boiler capable 

 of producing from 80 to 90 lb. pressure. 

 The method of sterilization is as follows : 

 before planting, prepare the soil in the 

 regular way, adding the necessary amount 

 of manure and fertilizers. At the bottom 

 of the bed or bench, pipes or drain tiles are 

 laid parallel to each other two feet apart. 

 The pipes are perforated with 1-6-inch 

 holes throughout. These pipes or tiles are 

 closed at the farthest end so that the steam 

 may come out through the cracks or holes. 



