376 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 4 



LEAKAGE OF FUMIGATION TENTS 

 By C. W. \\'ooDWORTn 



The purpose of the present paper is the discussion of the significance 

 of the leakage factor in fumigation and the development of a dosage 

 system which shall be based upon the varying conditions of leakage 

 tents found in actual operation in the field. 



Every one unacquainted with the facts regarding the conditions 

 under which fumigation is carried on will be inclined to enquire, " Why 

 have any leakage at all?" No doubt there can be and should be much 

 improvement in this respect but under the best conditions likely to 

 be obtained, this factor will still remain a very important element in 

 calculating the dose to be used. 



The practice of fumigation has been developed without scientific 

 supervision and the dose given to trees of varying sizes was determined 

 by "cut and try" methods and the actual system used as a result of 

 practical experience of hundreds of fumigators developed through a 

 quarter of a century of practical work is entirely at variance with the 

 suggestions of the scientific men who first developed the method. 



Many present, perhaps, do not appreciate that fumigation is not 

 only the most important insecticide operation in Cahf ornia as measured 

 by its cost, but also that it is more important than the combined insec- 

 ticide work of any other state or of any foreign country. 



The development of the process to such proportions, amounting to 

 an outlay of now about $500,000 per year, could only have occurred 

 where the average practice has become approximately correct. 



The first attempt to develop a system for the calculation of the dose 

 consistent with the practice of fumigation was in 1903.^ At that time 

 there was no data in existence for dose calculation corresponding even 

 approximately with the practice, and the scheduling of orchards was 

 exclusively by the judgment of the fumigator, acquired by observing 

 the work of the other fumigators and corrected from time to time by 

 results obtained in fumigation. 



Under such conditions there was bound to be much irregularity in 

 individilal cases even though the average results were certainly very 

 dependable. 



Several thousand m^easurements were made at that time showing 

 that the average dose of four ounces corresponded with an average ten- 

 foot tree; a dose consistently used by no fumigator but nevertheless 

 that established, and firmly established, by practice for the de- 

 struction of the black scale. 



iBulletin No. 152, California Experiment Station. 



