TOXIC GASES AS A CONTROL OF THE PEACH-TREE BORER. 
Hutchison, and Scales 1 reported rather indifferent results from its 
use against fly larvae in horse manure. Moore 2 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 evenly 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- 
iCoOK, F. C, Hutchison, R. H., and Scales, F. M. Further experiments in the 
DESTRUCTION OF FLY LARV.E IN HORSE MANURE. U. S. Dept. Agr. Bui. 245. 1915. 
2 Moore, Wm. Fumigation of animals to destroy their external parasites. In 
Jour. Econ. Ent., v. 9, no. 1, p. 71-78. 1916. 
