TOXIC GASES AS A COISTTROL OF THE PEACH-TREE BORER. 



Hutchison, and Scales^ reported rather mdifferent results from its 

 use against fly larvae in horse manure. Moore ^ used it in 1916 in the 

 fumigation of animals to destroy their external parasites and found 

 it less effective for that purpose than nitrobenzene. Its chemical 

 formulae and physical properties are discussed fully in Duckett's 

 report. It is a crystalline solid at ordinary temperatures, insoluble 

 in water, melting at 53° C, and boiling at 172° C. Like naphthalene 

 it vaporizes much below its boiling point, although only very slowly 

 at ordinary temperatures. Its vapor pressure and rate of volatiliza- 

 tion are discussed on page 21. Apparently, however, when vaporiza- 

 tion takes place in a closed container of a capacity appropriate to the 

 dose, or under conditions approximate to that, the evolution of gas 

 even at ordinary temperatures is sufficiently rapid to produce eventu- 

 ally an atmosphere of toxic saturation. 



Method of Application. 



The method of application for the use of p-dichlorobenzene 

 against the peach borer is illustrated in Plate I. The mechanical 

 condition of the material, on account of its relation to the rate of 

 evaporation, is of considerable importance. The action of the gas 

 is quite local and an even distribution about the tree is highly de- 

 sirable. It was found that p-dichlorobenzene was most convenient 

 and satisfactory for use when pulverized to about the fineness of 

 coarse salt or granulated sugar. The form in which it usually appears 

 on the market may be reduced to this condition by crushing and 

 sifting through a 12-mesh screen. In this condition it does not 

 lump badly, can be evenlj^ distributed, and vaporizes at about the 

 proper rate. 



In making application the soil crust is first broken to a depth of 

 1 or 2 inches with a hoe, or some other suitable tool. The vapor of 

 p-dichlorobenzene is about five times heavier than air and it is not 

 desirable to apply it deeper than is necessary to avoid washing and 

 surface loss of gas. The soil is not scraped away from the collar of 

 the tree unless there is a decided mound. The material is placed 

 as nearly as possible at the level of the uppermost galleries. The 

 soil, moreover, should not be disturbed except to break up the surface 

 crust. The gas will permeate very tight soils readily, and any un- 

 necessary digging up of the soil about the collar only makes more air 

 space to be saturated, and increases the chance of ineffective fumiga- 

 tion. After the preparation of the soil surface the p-dichloroben- 

 zene is sprinkled as evenly as possible about the collar of the tree 

 in a band 1 or 2 inches wide. In practice the material may be con- 



1 Cook, F. C, Hdtchisox, R. H., and Scales, F. M. Further experimexts ix the 



DESTRUCTION OF FLY LARV.E IX HORSE MANURE. U. S. Dept. AgT. Bul. 245. 1915. 



= Moore, Wm. Fumigation of animals to destroy their external parasites. In 

 Jour. Econ. Ent., v. 9, no. 1. p. 71-78. 1916. 



