54 FUMIGATION FOR THE CITRUS WHITE FLY. 



varieties. Grapefruits are slightly susceptible to this injury, while 

 tangerines appear not at all susceptible, although considerable shed- 

 ding of the fruit occurred in one instance when the recommended 

 dosage was doubled. 



SUGGESTIONS FOR THE FUMIGATION OF SMALL TREES. 



IN THE GROVE. 



In discussing the style of fumigating tents desirable for use against 

 the white fly the author has referred to the advantages of the use of 

 box covers for small trees. In many cases complete defoliation of 

 the trees during the winter months would be the best method of 

 checking the pest, but fumigation is preferable under most circum- 

 stances. The dosage with box covers will depend upon the tightness 

 of the cloth used. It has been recommended that the cloth be made 

 as nearly air-tight as possible by means of paint, or that air-tight 

 oilcloth be used. The rate of dosage can be readily determined by 

 means of a series of tests, beginning with 1 ounce of potassium 

 cyanid for each 170 cubic feet of space (0.00588 ounce per cubic 

 foot) and decreasing the number of cubic feet per ounce 10 feet for 

 each experiment until the results are satisfactory and uniform. No 

 experiments have thus far been conducted by the author along these 

 lines, but it is expected that in the course of the investigations of 

 the white fly now under way in Florida this phase of white fly con- 

 trol will be given consideration. 



IN THE NURSERY. 



Several square yards, including many trees, can be covered in the 

 nursery by a single tent. If the cloth is unpainted, the dosage for a 

 first trial can be calculated by first determining the ratio of the leak- 

 age surface to the cubic contents and referring to Table VIII in this 

 bulletin, where the recommended rate of dosage will be found for the 

 various ratios. The results of the preliminary tests should be care- 

 fully observed before fumigating on a large scale, in order that the 

 rate of dosage may be adjusted to suit the tightness of the cloth used 

 as a cover. 



NURSERY STOCK FOR SHIPMENT. 



Prof. H. A. Gossard, formerly of the Florida experiment station, 

 has determined that in an air-tight fumigatorium 1 ounce of potas- 

 sium cyanid for each 170 cubic feet of space" is sufficient to destroy all 



« "One gram to 6 cubic feet of space," he reports, "seemed sufficient to kill every- 

 thing, but to make the dose more certain 1 gram to 5J cubic feet was adopted as the 

 standard dose and has been repeatedly tried, always giving the uniform result of kill- 

 ing all larvfe (pupae) and adults." — Bui. 67, Fla. Exp. Sta., p. 652. One ounce is 

 equal to 28.35 grams, from which it is calculated that 1 gram for 6 cubic feet of space 

 is equal to 1 ounce for 170 cubic feet and 1 gram for 5| cubic feet is equal to 1 ounce 

 for 163 cubic feet. 



