30 FUMIGATION FOR THE CITRUS WHITE FLY. 



MEASURING TREES. 



Necessity for measurernents. — The rule followed by some California 

 fiimigators 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 wliite fly and one which would produce injury to the 

 tree is not large in many cases," and careful estimation of dosage 

 seems essential for economy and success in fumigation for this insect. 

 Even among f umigators considered most successful in California, there 

 is a wide 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,'' 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 wliich 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 Avill, by 

 insuring satisfactory results, prove the most economical for adoption 



a The experimental work conducted in Florida during the winter of 1907^8 has 

 shown that the liability of injuring citrus trees from overdosing is 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. 



b Water-shrunk or its equivalent as regards tightness. It should be borne in mind 

 that mildew-proofing with tannin, etc., is not supposed to increase tightness more than 

 does the normal shrinking. 



