INJURY TO FOLIAGE BY ARSENICAL SPRAY MIXTURES ‘ 
By D. B. SwiNGEE, Botanist, H. K. Morris, Assistant Botanist, and Edmund Burke, 
Chemist, Montana Agricultural Experiment Station 
INTRODUCTION 
Since the first trials of Paris green and of arsenic trioxid for the con¬ 
trol of the potato beetle half a century ago there has been a constant 
increase in the use of arsenical compounds for controlling the ravages of 
certain species of insects on economic plants. 
It is a notable fact that of the many poisonous substances known to 
physiological chemistry none has been found so well suited to the purpose 
of poisoning insects that obtain their food by gnawing away portions 
of the fruit and foliage as certain arsenical compounds. As the control 
of such insects is a very important field in the science of entomology, 
much practical and scientific interest centers around this group of com¬ 
pounds. This interest makes imperative the obtaining of more informa¬ 
tion along certain lines; for it is agreed that an arsenical compgund to 
be a satisfactory insecticide for application to foliage shall approach 
perfection in these respects: (i) It must promptly kill a large propor¬ 
tion of the insects; (2) it must be relatively inexpensive; (3) it must not 
seriously injure the plants to which it is applied under the conditions 
obtaining. Unfortunately, no compound has yet come to notice that 
perfectly satisfies these requirements, though several do so sufficiently 
well to be extensively used. It is with the third requirement that this 
investigation deals, although the others are constantly kept in mind. 
The problem of arsenical injury to fruit trees and garden crops as a 
result of spraying is a troublesome one. Some of the compounds first 
tried have been abandoned or greatly restricted because of the injury 
produced and new ones have been proposed to take their places; and 
these in turn may yet give way to others. 
It has long been evident that there are factors influencing arsenical 
injury that the horticulturist does not understand • and others that he is 
powerless to control. Considerable work has been done to show the 
nature and relative importance of these factors. All of this work has 
been fragmentary and most of it has been done under such conditions 
that it is impossible to judge the relative importance of two or more 
factors operating at the same time. In most cases the exact composi¬ 
tion of the mixture used was not known and in many cases the fact 
that quite different chemicals appear under the same name evidently 
was not even suspected. Some of the conclusions drawn are quite con¬ 
tradictory, and others, though perhaps correct, are based on so little 
evidence that their soundness is questioned. It is probably safe to say 
that at the time this investigation was undertaken at this station in 
1912 enough correct conclusions on this subject had already been drawn 
to make certain phases of this work largely unnecessary if these correct 
conclusions had been recognized and isolated from the mass of apparently 
conflicting data and theories. Such a distinction had, however, been 
found impossible. 
1 Accepted for publication Sept. 2, 1922. 
Journal of Agricultural Research, 
Washington, D. C. 
aeq 
(soi) 
Vol. XXIV. No. 6 
May 12, 1923 
Key No. Mont.-ii 
