30 FUMIGATION FOE THE CITRUS WHITE ELY. 
MEASURING TBEES. 
Xu-fssity for measurements. — The rule followed by some California 
fumigators in estimating the dosage for scale insects is to give an 
amount which in the manager's judgment is as large as each tree will 
stand without injury to well-matured growth. Tender growth is 
almost invariably injured by a proper dosage, but this loss is not con- 
sidered of consequence. In Florida, however, there is usually little or 
no new growth until toward the close of the season to which fumi- 
gation for the white fly should be limited. It is obviously impos- 
sible, even for an experienced fumigator, without measuring, to 
judge of the size of trees so accurately as to avoid overdoses, on 
the one hand, wasting a small percentage of the chemicals, and, on 
the other hand, underestimates with the consequent lack of effec- 
tiveness. The difference between an effective dosage as a treat- 
ment for the white fly and one which would produce injury to the 
tree is not large in many cases, a and careful estimation of dosage 
seems essential for economy and success in fumigation for this insect. 
Even among fumigators considered most successful in California, there 
is a Ancle diversity of opinion as to the quantity of chemicals required 
for trees of the same size, as shown by the observations of Mr. S. J. 
Hunter, reported by Professor Woodworth, and by the published rec- 
ommendations as to dosage by various writers. The significance of 
this in California is that there is a great difference between efficiency 
against the scale insects treated and danger to the trees; and the prac- 
tice of basing dosage on guesses as to the dimensions, either before or 
after covering, necessarily results in the danger of underestimation of 
the dosage requirement on the one hand and a needless waste of 
chemicals on the other. A study of the table given in the appendix, 
showing the dosage recommended for successful work against the white 
fly with untreated tents, 6 proves the physical impossibility of a fumi- 
gator approximating such dosage without a definite knowledge of the 
size of the space inclosed and of the ratio of the number of cubic feet of 
contents to the square feet of surface through which the gas gradually 
escapes. This can be obtained only by actual measurements. The 
only two dimensions which it is at all practicable to obtain are the 
circumference of the tented tree at the base and the distance over the 
top from ground to ground. The system here recommended will, by 
insuring satisfactory results, prove the most economical for adoption 
« The experimental work conducted in Florida during the winter of 1907-8 has 
shown that the liability of injuring citrus trees from overdosingis frequently depend- 
ent upon the physiological condition of the trees as affected by the nature of the 
soil, the soil moisture, and the chemical fertilizers used in the' grove. 
& Water-shrunk or its equivalent asregards tightness, li should be home in mind 
thai mildew-proofing with tannin, etc., is not supposed to increase t ightness more than 
does the normal shrinking. 
