TOXIC GASES AS A CONTROL OF THE PEACH-TREE BORER. 3 
ber active on untreated trees in adjoining rows. In all cases the effect 
of the fumigation on the tissues of the tree was carefully noted, 
the margin of safety being considered as fully as the larvicidal 
action of the gas. Injury to the trees has been classified under 
the following terms: Trace, slight, moderate, severe, and maxi- 
mum. Maximum injury applies to cases where the tree has been 
girdled completely by the fumigation, and no doubt remains of 
its immediate death. Severe injury indicates that the tree has been 
girdled partially, sufficient to destroy permanently its productive 
value, but not to cause its immediate death. The other terms, moder- 
ate, slight, and trace, represent a gradually diminishing degree -of 
injury, the last term indicating that the effect of the gas was only 
sufficient for identification. The first two terms, trace and slight, 
represent injury which is of little or no importance as far as the 
effect upon the tree is concerned. 
EXPERIMENTAL RESULTS. 
MISCELLANEOUS GASES. 
The principal materials that have been tested are carbon disul- 
phid, carbon tetrachlorid, hydrocyanic-acid gas, naphthalene, and 
para-dichlorobenzene. In the discussion of the relative merits of 
these materials the results are given in detail only for the last, p-di- 
chlorobenzene. 
Carbon Disulphid. 
In 1902 Woodworth 1 recommended the use of carbon disulphid 
against the western species of peach borer. Under the proper con- 
dition of soil moisture and temperature it is a most efficient larvicide. 
In practice, however, it was found impossible to standardize its use 
to an extent which would make it both safe and effective. The main 
difficulty with this material arises from its great volatility at or- 
dinary temperatures, which makes it very sensitive to variations in 
soil porosity. In very dry or jDorous soils, large doses of several 
ounces may be applied with no effect upon the larvae. On the other 
hand, in very moist, tight soils, large vigorous 12-year old trees 
have been entirely girdled by an application of as small a dose as 
one- fourth of an ounce. Its application in water emulsion was 
found to standardize soil conditions greatly, and successful treat- 
ments by this method with greatly-reduced doses have been made on 
hundreds of trees without injury. A very slight mis judgment in 
dosage for a given set of conditions, however, gave results of an 
opposite character, and after two and one-half years' experience with 
this gas its use has been entirely abandoned. 
1 Woodworth, C. W. The California peach-tree borer. Cal. Agr. Exp. Sta. Bui. 
143. 1902. 
