FUMIGATION VEESUS SPKAYING. 63 



The tented tree shown in Plate YI, figure 2, measured 42 feet over 

 the top from ground to ground and 59 feet in circumference. 

 According to the table given in the appendix a tree of this size 

 should be given 26 ounces of potassium cyanid. In covering a tree 

 of this size ordinary changing poles could be used instead of the up- 

 right sho\vn in the illustration. The entire cost of fumigating the 

 tree for the white fly is estimated at 50 cents. This includes 36 cents 

 cost of potassium cyanid, 3 cents cost of acid, 6 cents cost of labor, 

 and 5 cents cost of wear and tear on the tent. The tree shown at the 

 left of the tent in Plate VI, figure 2, measured 44 feet over the top and 

 53 feet in circumference. According to the tables the tree requires 25 J 

 ounces of potassium cyanid, the cost of fumigating therefore being 

 practically the same as for the first tree mentioned. Each of these 

 trees if sprayed would require six or seven gallons of hquid at each 

 apphcation. Three applications in e year at the usual cost would be 

 from 45 to 63 cents as compared with 50 cents for fumigating. The 

 tree shown in Plate I measured, when tented, 33 feet over the top and 

 38 feet in circumference. A tree of this size requires 12 ounces of potas- 

 sium cyanid for effective fumigation. The total cost of one fumiga- 

 tion would be about 27 cents, including 16 cents as cost of potassium 

 cyanid, 6 cents as cost for labor, 1 cent as cost for acid, and 4 cents for 

 wear and tear on the fumigating tent. A tree of this size would 

 require at least 3 gallons of spray at each application, and during the 

 year the cost for three appHcations would be from 22 to 27 cents. * 



These data on the comparative cost of the two methods of control 

 show that the advantage of fumigation over spraying for the first year 

 is a matter of greater efficiency, except when more than three applica- 

 tions of spray are made, when fumigation is also less expensive. 

 Fumigation, however, in an isolated grove or under favorable condi- 

 tions as to location, when properly conducted would not require repeti- 

 tion for two or more years. The best of spraying could not, unless aided 

 by abnormal climatic conditions, so reduce the white fly that the num- 

 ber of applications could be lessened the second year without interfer- 

 ing with the degree of success attainable by the practice. In two years 

 the cost of spraying the trees above referred to would double the cost 

 of one fumigation. In a series of five or more years spraying would 

 doubtless cost fully three times as much as would control by fumiga- 

 tion, the labor involved would be far greater, and the results far less 

 satisfactory. 



FUMIGATION VERSUS NATURAL CONTROL. 



The present investigation of the wliite fly by the AVTiter and his 

 associates covers all phases of the subject. Due consideration is given 

 to all possible sources which give basis for the hope of effecting eco- 

 nomical control. The exposed condition of the pest under considera- 

 tion, its vulnerabihty to attack by natural enemies, the high degree 

 of humidity in the citrus-gTo^^^ng regions of the Gulf States which 

 49918— Bull. 76—08 5 



