206 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 13 
chemical analysis will only show a trace. In five weeks a chemical 
analysis of the soil fails to show a trace of cyanide. When two or 
three ounce treatments have been made a faint trace of cyanide 
(chemical analysis) will exist in the soil adjacent to the tree five weeks 
after the applications have been made. It was also observed that 
sodium cyanide disappears sooner in liquid treatments than when the 
dry granular material was used. 
The physical and chemical consistency of the soil has some bearing 
upon the use of poisonous gases for the control of the peach borer, but 
its importance (when using sodium cyanide) has not been thoroughly 
worked out. Our experiments show that one ounce treatments produce 
a greater percentage of dead larvse when the trees are situated in light 
sandy soils than when located in heavy soils. This may be due to the 
fact that the gas penetrates light soils more rapidly and to a greater 
distance than heavy soils. Heavy soils are usually water laden and 
this may prevent a rapid and thorough distribution of the gas. The 
water holding capacity of a soil may prove to be an important factor 
in the use of sodium cyanide and other poisonous gases. 
Time of Application 
The time of application is important. Our results show that appli¬ 
cations in May, June, September, and October, give the best results 
in killing the larvse and is the safest for the tree. As yet tbe results do 
not conclusively show which of these months is the best; however, I 
am of the opinion that the last week in September or the first week in 
October will probably be the best time in New Jersey. At this time 
all of the eggs have hatched and the majority of the young larvse will 
be found on the outside of the tree or just beneath the outer surface 
of the bark. 
Summary 
Sodium cyanide is a very poisonous substance; consequently one 
must use extreme care in making applications. On account of the 
poisonous nature of sodium cyanide it is doubtful if anyone would 
deem it wise to make a general recommendation to peach growers for 
its use. 
From a scientific standpoint it has been interesting to note its in¬ 
fluence on the larvse and the peach trees. The results obtained may 
give us some information on the use of other substance such as para- 
dichlorobenzene. During 1919 we used paradichlorobenzene in two 
orchards, but our experiments to date are not sufficiently extensive or 
conclusive to give the results at this time. 
One ounce treatments (liquid or granular form) of sodium cyanide 
will kill 75 to 90 per cent of the larvse in five- to ten-year-old trees. 
