April, ’24] 
CHANDLER: PARADICHLOROBENZENE 
247 
gas decay rapidly, and if treatments are left for from 4 to 6 weeks 
before examinations are made, few dead worms are found, though live 
larvae are usually easily located. To be conservative, however, I 
have not based my percentages of kill on the number in the check trees. 
Table 1. A Comparison of the Results of P. D. B. Treatment on Peach 
Trees from which Grass, Weeds, and Gum Had Been Removed 
Prior to Application, with Trees in Which this was not Done. 
Treatment 
Examined 
No. of 
Removed 
% 
Not removed 
% 
Applied 
trees 
Live 
Dead 
kill 
Live 
Dead 
kill 
Oct. 12, ’22 
Nov. 13 
6 
0 
2 
100 
0 
3 
100 
Check 
“ 21 
6 
7 
0 
May 23, ’23 
June 18 
10 
3 
12 
80 
3 
18 
85.7 
Check 
i l U 
5 
9 
0 
Sept. 15, ’23 
Oct. 20-22 
10 
0 
4 
100 
1 
5 
83.3 
O 
o 
CF 
}— 4 
Oct. 22 
10 
2 
17 
89.4 
1 
13 
92.8 
“ 13, “ 
“ 27 
10 
13 
51 
79.6 
1 
12 
92.3 
n a u 
i i a 
10 
5 
9 
64.21 
Check 
“ 22 
10 
28 
0 
*Dirt removed such that P. D. B. was applied at level lower than some of the 
burrows. 
Effect of Rains 
As the killing agent in P. D. B., is a gas which penetrates to the burrows 
thru the air spaces in the soil, it would be reasonable to expect that 
rains filling these air spaces would retard or prevent the passage of the 
gas, and that it would be useless to treat immediately after soaking 
rains; also that a treatment applied just before a period of heavy pre¬ 
cipitation would not be very effective. To spread some light on the 
question, weather records were examined in connection with the ex¬ 
perimental work of the past four years, and data compiled which is 
presented in Table II. 
These data show eleven cases in which rainy periods of from 4 to 11 
days, with precipitations averaging 3.19 inches, immediately preceded or 
followed treatments which gave kills of 77% to 85% in the springs, and 
80% to 100% in the falls. 
Young Trees Not Injured 
The first experimenter with P. D. B., advised against its use on trees 
younger than 6 years of age. Other workers in Eastern states have re¬ 
ported injury on young trees. Following these men, a number of 
writers have included in their recommendations the caution not to 
treat young trees. 
