Methods of Control 385 



clean paper. The sulphur is then placed in wide, 

 deep metal pans at the bottoms of which are first 

 placed chips which have been soaked in kerosene. 

 The pans are solidly placed at equal distances on 

 raised bricks in the center aisle of the house. When 

 all is in readiness fire is set to the chips. When 

 these begin to burn well the sulphur is spread evenly 

 on the burning chips of each pan. As soon as the 

 sulphur ignites, the operator should run out and shut 

 the door of the house as quickly as possible. Sulphur 

 fumes have an irritating and suffocating effect on 

 man. The sulphur fumes should be allowed to act 

 for at least twelve hours before one opens the house. 

 The sulphur fumigation may be started at any con- 

 venient time during the day or night. This treat- 

 ment will destroy red spider and mildew. 



Hydrocyanic-Acid Gas, There seems no doubt 

 that fumigation with hydrocyanic gas offers the 

 cheapest and most efficient method of controlling 

 white flies, aphids, thrips, scales, and mealy bugs. 

 However, this method has not yet gained general 

 popularity because of the deadly nature of the gas 

 and its injury to plants when overdone. The best 

 generators for the gas are one-half or one gallon 

 glazed earthenware jars. When ordering generators 

 it should be indicated that tops are not desired. 



Before fumigating it is essential to see that all 

 broken glass is repaired, and that all cracks are care- 

 fully stopped up. It is very essential that the cubi- 

 cal contents of the greenhouse be accurately deter- 

 mined. To secure the cubical contents of an even 



