56 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 



Other conditions exist which take part in prohibiting this greater 

 dosage. If this dosage were used in general orchard work, it is doubt- 

 ful if eradication would occur hi all cases. Tents not properly 

 pulled down on all sides of the tree, a hole in the tent, mistake hi 

 measuring the trees or hi reading the dosage from the schedule, 

 erroneous measuring of chemicals, boiling over of a generator, over- 

 turning of a generator, and numerous other considerations which will 

 sometimes escape even the most careful manipulator, make the differ- 

 ence between eradication and noneradication more variable hi prac- 

 tice than hi theory. If the fumigator is inclined to be a little careless, 

 some of the above errors will frequently creep in. 



Moreover, unless compelled to do so the orchardists hi any one 

 locality would not all use this dosage, while possibly some would not 

 fumigate at all. To go to the extra expense required hi an eradication 

 dosage and then be subject to rehifestation from one's neighbors 

 presents no special attractiveness to the grower. Supposing that 

 the growers hi any one locality were willing to use an eradication 

 dosage, the present number of fumigation outfits is inadequate to 

 meet this requirement within the limited time necessary in order to 

 prevent rehifestation. These practical considerations demonstrate 

 that the eradication of the purple scale from any large district is im- 

 practicable at the present time. 



DIFFICULTY OF DESTROYING THE SCALE OX THE FRUIT. 



There is one more important point which must be considered in 

 connection with fumigation for the purple scale. In experiments 

 to which attention has been called it has been shown that destruction 

 of scale is much more difficult on the fruit than on the leaves and 

 branches. Careful investigation of this point for about two years 

 has also shown that the susceptibility of the scale on some fruit is 

 much greater than on others. Hence, no exact standard of destruc- 

 tion for the scale on fruit is possible. TVhen scales become matured 

 and deposit eggs the dosage required for eradication is very much 

 greater on the fruit than on the leaves and branches. It may require 

 a one-fourth to one-half or hi some cases an even greater increase. 

 A dosage sufficient for eradication of the scale on the fruit is impracti- 

 cal for the very same reasons that make eradication on the leaves 

 and branches commercially impractical. A grower possessing a 

 few trees on which he intends to eradicate the scale at one fumigation 

 should remove all infested fruit before the operation and then use a 

 1§ schedule. It is advisable to remove the old scaly fruit hi any fumi- 

 gation. At picking, fruit badly hifested with scale is usually left on 

 the tree, and frequently from one to a half dozen or more old, scale- 

 infested oranges per tree remain throughout an orchard. Even after 

 a good fumigation one of these old fruits might carry more healthy 



