80 



CALIFORNIA CITRUS CULTURE. 



IMstnnoe over tree. 



FIG. 54. Schedule No. 1. The first few dosages should be doubled. 

 (U. S. Dept. Agrcl.) 



LENGTH OF EXPOSURE. 



The time required to complete the generation of the gas is not long, 

 but it is advisable to leave the tents upon the trees for at least forty-five 

 minutes after the dosage is placed under the tent. Some prefer thirty 

 minutes, while others insist upon a full hour. 



TIME OF OPERATION. 



For red, purple and yellow scale fumigation work is usually done 

 during the winter or spring months. If black scale is present the time 

 of operation covers the period from the middle of August to the middle 

 of January, depending somewhat upon the individual locality. 



TEMPERATURE. 



To avoid the heat of the sun, fumigation is ordinarily done during the 

 night, when the atmosphere is cool. Cloudy cool days may admit of 



