250 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
Cumulative Effects of P. D. B. 
Altho we have no authentic record in Illinois of injury to peach trees 
from P. D. B., where applied in the proper manner, the question arises 
as to whether we can continue to use it }^ear after year with no ill effects. 
Some data bearing on this point are given in Table III. This shows a 
total of 200 acres treated for 4 successive years and 115JJ acres for 3 
successive years, all with no ill effects. Ages of trees when treatment 
was first begun ranged from 1 to 10 years. The record of effect on 
trees was secured both from personal observation and talks with the 
owners. 
Table III. Cumulative Effects of P. D. B. 
Present Yrs. Effect on Trees 
Orchard Place Age—Yrs. No. acres Treated 
Amer. Fruit Growers. Cobden 3-12 200 4 No ill effects. 
Paul Miller.Anna 5-7 50 3 “ “ 
J. C. Hundley.Carbondale 3 10j4 3 “ “ “ 
John A. Gage.Texico 7 5 3 
Guy Beauman.Tunnel Hill 7 50 3 
The Effect of P. D. B. Touching the Bark 
Users of P. D. B., have generally been cautioned against allowing the 
material to touch the bark of peach trees. In my own experimental 
work I have observed no injury when a few crystals have come into 
contact with the bark. To determine this point, four 1-yr. old trees 
were treated at Anna, in May 1922, using oz., per tree, packing it 
close against the bark. In July, these 4 trees were apparently as healthy 
as the other treated trees, but in September one was seen to be dying, 
and a dead area was found around the base of the trunk. At that 
time seven 1-yr. trees were treated in a similar manner at Ozark. Ill. 
In March, 1923, 6 of the 7 were observed to be dead at the base, tho 
the tops were still green. One of the seven was accidentally removed 
during the summer, but on September 12, the date of my last examina¬ 
tion, 5 of the 6 were entirely dead, tho trees of the same age treated in 
the regular manner, were uninjured. 
P. D. B. on Apple 
To the writers knowledge the only experimental work on the use of 
P. D. B., on apple, (the results of which have been published) was 
carried on by E. B. Blakeslee in Springfield, W. Va., and recorded in 
U. S. D. A., Bui. 796. In this experiment 12 three year old apple trees 
