CONTENTS 
Page. 
Introduction 9 
Extent of citrus orchards 10 
Citrus pests K) 
Insect enemies of citrus fruits, and their distribution LO 
Injury resulting to scale-infested trees II 
Method of propagation of the more injurious scale pests L6 
Methods used in the control of scale pests of citrus trees L6 
Fumigation 17 
Sheel 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 eyanid 30 
Sulphuric acid 30 
Proportion of chemicals used by fumigators 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 13 
The length of exposure 44 
Kradieation of the purple scale 46 
Difficulty of destroying the scale on the fruit 46 
( reneral considerations 47 
Leakage of gas during operations 47 
Time of the year for fumigation 48 
Fumigation during the blossoming period 49 
Fumigation while I he fruit is of .-mall size 51 
5 
