FUMIGATION VERSUS SPRAYING. 68 
The tented tree shown in PlateVI, figure 2, measured 12 feet over 
the top from ground to ground and 59 feel in circumference. 
According to the table given in the appendix a tree of this size 
should be given 26 ounces of potassium cyanid. En covering a tree 
of this size ordinary changing poles could be used instead of the up- 
right shown 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 o'i wear and tear on t he tent . The tree shown at the 
left o\' the tent in Plate VI, figure 2, measured I I feet over the top and 
53 feet in circumference. According to the tables the tree requires 25 J 
ounces o( potassium cyanid, the cost of fumigating therefore being 
practically t ho same as for the first tree mentioned. Each of these 
trees if sprayed would require six or seven gallons of liquid at each 
application. Three applications in a year at the usual cost would be 
from 45 to 63 cents as compared with 50 cents for fumigating. The 
tree shown in Plate 1 measured, when tented. 33 feet over the top and 
38 feet in circumference. A tree of this size requires 1 2 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 cent- 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 applications would be from 22 to 27 cent-. 
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 twoor 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 white fly by the writer and his 
associates covers all phases of t he subject . Due consideration is given 
to all possible sources which give basis for the hope of effecting eco- 
nomical control. The exposed con lition of the pest under considera- 
tion, its vulnerability to attack by natural enemies, the high degree 
of humidity in the citrus-growing region- of the Gulf State- which 
49918 Bull. 76 08 5 
