4 FUMIGATION INVESTIGATIONS IN CALIFOENIA. 



the moister coastal strip; for difTerent seasons of the year; and for the 

 difTerent growing conditions of the tree, as whether in fresh leafage, or 

 in bloom, or with different stages of the developing fruit. 



(2) Physiological effect on the tree and fruit. There is some evi- 

 dence to show that the gas may have a stimulating effect on the tree. 



(3) Mechanical equipment. An important economical considera- 

 tion in gassing is the employment of the most suitable tent cloths, and 

 their treatment to give durability and imperviousness ; also, the best 

 mechanical means of hoisting tents over the trees. To be determined 

 under this heading also are the most economical methods of generating 

 the gas, and an indication of the quality of chemicals best suited for 

 the purpose. 



In connection with this experimental work the scale species them- 

 selves are being given a careful study in the field to determine their 

 exact life history as a basis for the intelligent application of the 

 remedy. 



This investigation was started in July, 1907, under the field charge 

 of Mr. R. S. Woglum, who first made himself thoroughly familiar 

 with the problem by a personal examination of conditions throughout 

 the citrus-growing regions of southern California. The direct work 

 of investigation began as soon as the fumigation season opened, and 

 later Mr. Frederick Maskew was employed to assist in the work. The 

 experimental work as planned has been conducted on a commercial 

 scale, so that the conditions and results will be those normal to the 

 ordinary care of citrus groves. To carry out all the lines of experi- 

 ment indicated above, and the subsidiary ones which have developed 

 in the course of the investigation, takes a good deal of time, and will 

 probably occupy two or three years with the money and force now 

 available. Nevertheless, very considerable progress has been made, 

 and the preliminary report herewith submitted covers the general 

 features of fumigation procedure. 



Improved methods have been devised, and these are being very 

 rapidly adopted throughout southern California. These improved 

 methods make it possible to do much more uniform work and greatly 

 simplify the method of estimating the proper dosage. Full atlvantage 

 has been taken of the fumigation work conducted in Florida against 

 the white fly under the field direction of Dr. A. W. Morrill, and the 

 Morrill system of marking tents for the ready determination of dosage 

 has been introduced, with modifications, into California. 



C. L. Marlatt, 

 Entomologist and Acting Chief of Bureau in Absence of Chief. 



