246 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
SOME RECENT DEVELOPMENTS IN THE USE OF 
PARADICHLOROBENZENE 
By S. C. Chandler, Illinois State Natural History Survey 
Abstract 
Experiments and observations on the peach borer, Aegeria exitiosa Say, in Illinois 
during the past four years have brought out the following facts about paradichloro- 
benzene.* 1. Grass and weeds need not be removed from around the base of the 
tree before applying the chemical. 2. Heavy rains just before or just after treatment 
do not appear to effect the action of the gas. 3. One year trees have not been injured 
when treated with P. D. B., in the proper manner. 4. It is not necessary to remove 
dirt from around the trees after treatment. 5. Up to the present time, there have 
been no injurious cumulative effects of P. D. B., in Illinois. 6. P. D. B., packed 
closely against the bark of young peach trees will kill a large percentage of the trees. 
7. No injury was produced by P. I). B., in experiment with apple trees. S. 2 oz. 
application per tree is suggested as advisable for 12 year old trees. 
As a result of four years of experimental work and observation in 
southern Illinois, some new and interesting conclusions have been 
reached on the use of paradichlorobenzene 1 . 
Removal of Grass and Weeds 
The common practice of scraping away grass and weeds from around 
the bases of peach trees before treating with P. D. B., is open to two 
objections, viz., it takes too much time, and there is a tendency to scrape 
away so much dirt that the chemical is applied below the point where 
some of the borers are feeding. This latter point is brought out in 
Table 1, which shows only 64% kill where applied too low. 
Experiments to determine the necessity of removing grass and weeds 
before applying P. D. B., were begun in a small way in the fall of 1922, 
and followed up in the spring and fall of 1923. Trees 5 years old were 
selected for this purpose, in uncultivated and uncared for orchards in 
order to secure an excessive amount of grass and weeds, more than would 
usually be encountered. 
By referring to Table 1, it will be observed that in 4 out of 5 trials dur¬ 
ing the three seasons in which the experiments were carried on, as good 
results were obtained where grass and weeds were not removed as 
where removed. The percentages of kill varied from 92% to 100%' 
where not removed, and 79% to 100% where removed. In the course of 
these experiments a fact was brought out that I have observed every 
year in experimental work with this material, that worms killed by the 
Paradichlorobenzene, for convenience sake, has been called P. D. B., (Painless 
Death to Borers). 
