CONTENTS. 1 



Page. 



Fumigation of citrus trees B. S. Woglum. . 1 



Historical 1 



Recent renewal of interest in fumigation in California 2 



Extent to which fumigation is practiced in California 3 



The various systems of fumigation 4 



By contract 4 



By associations 5 



By counties 5 



By private individuals 5 



Extent and character of citrus orchards 6 



Insect enemies of citrus fruits 7 



The purple scale (Lepidosaphes beckii Xewm.) 8 



The black scale (Saissetia olese Bern.) 8 



The red scale {Chrysomphalus aurantii Mask..) 9 



The yellow scale ( Chrysomphalus citrinus Coq . ) 10 



The mealy-bug (Pseudococcus citri Risso) 10 



Apparatus 10 



Tents 10 



Poles and derricks 20 



The McFadden machine 21 



Supply cart and supply wagon 22 



Generating vessels 24 



General procedure 24 



Calculating the dosage 27 



Securing the measurements around and over 28 



The old method of procedure 30 



An improved system of fumigation 32 



Leakage of gas 33 



Dosage schedule 34 



Procedure 37 



Advantages under this system 37 



Experience with this system 38 



The chemicals in fumigation 40 



Potassium cyanid (KCN) 40 



Sulphuric acid (H 2 S0 4 ) 41 



Water as a factor in fumigation 44 



The most economical proportion of chemicals to use 47 



The amount of chemicals in very small dosages 48 



Mixing the chemicals 48 



Effect of the presence of sodium chlorid on the amount of gas given off. 49 



Nature of the residue 50 



Dosages for various scale pests 51 



Factors which affect the dosage 52 



The purple scale 53 



The red scale. 57 



The black scale 59 



The yellow scale 60 



Dosages in general fumigation 61 



1 The three papers constituting this bulletin were issued, the first on May 13, 1911, and the last two on 

 May 10, 1911. 



vn 



60477— Bull. 90—12 2 



