CONTENTS. 



Page. 



Introduction 9 



Extent of citrus orchards 10 



Citrus pests 10 



Insect enemies of citrus fruits, and their distribution 10 



Injury resulting to scale-infested trees 14 



Method of ^propagation of the more injurious scale pests 16 



Methods used in the control of scale pests of citrus trees 16 



Fumigation 17 



Sheet tents 17 



Points on procedure 18 



Dosage schedules of the more important writers on fumigation 19 



The present system of scheduling dosage 23 



The initial problem confronting this investigation 24 



Method of computing volume and dosage for tented trees 25 



Methods for obtaining the measurements and dosage of trees 26 



The chemicals required in fumigation 30 



Potassium cyanid 30 



Sulphuric acid 30 



Proportion of chemicals used by f umigators 32 



The amount of sulphuric acid necessary 32 



The effect of too great an excess of acid 34 



Water as a factor in fumigation 34 



The effect of different proportions of water on the temperature of the 



gas 35 



The temperature of the gas where large and small dosages are used 36 



The effect of different proportions of water on the amount of available 



hydrocyanic-acid gas 37 



The correct proportion of water 38 



The most economical proportion of chemicals to use in generating 



hydrocyanic-acid gas 39 



Mixing the chemicals 39 



Purple-scale fumigation 40 



Preliminary experiments for the control of the purple scale 40 



The leakage of gas in fumigating small trees 43 



The length of exposure 44 



Eradication of the purple scale 46 



Difficulty of destroying the scale on the fruit 46 



General considerations 47 



Leakage of gas during operations 47 



Time of the year for fumigation 48 



Fumigation during the blossoming period 49 



Fumigation while the fruit is of small size 51 



5 



