INSECTS INJURIOUS TO CITRUS FRUITS 621 



These fungi are generally introduced or distributed in scale- 

 infested trees by tying small pieces of fungus material (2 or 3 inches 

 long) to twigs or branches having the most scale. The fungus 

 material may also be rubbed up in water and the resulting infusion 

 of spores and water sprayed into the trees or mixed with the 

 infusion of spores used for distributing the whitefly-fungi 



Fumigation.* 



By all means the most popular and efficient means of control 

 for citrus fruit insects in California is fumigation with hydrocyanic 

 acid gas. General discussion of the nature of this gas and its 



FIQ. 533. Fumigation of citrus trees. Some steps in preparation. After 

 Woglum, U. S. Dept. of Agr. 



preparation will be found in the chapter on insecticides in this 

 volume. The application of the process to outdoor conditions for 

 use to kill insects on trees is, in itself, a matter of special study. 

 The work in California is usually done by contract by concerns 

 which make that work their business, but the grower should have 

 an idea of the nature of the process in order to be able to tell 

 whether the work is being done properly. 



The fumigating season extends from August to January and 

 the work should be done when the temperature is not either 

 unusually high or unusually low. It is usually done during the 

 night. 



*See R. S. Woglum, Farmers' Bulletin 823, U. S. Dept. of Agr. and 

 bulletins of the California Agr. Expt. Station. 



