4 
Colorado Experiment Station 
there is great danger of our adding arsenic enough in the form of 
materials used for spraying to jeopardize not only the life of the trees 
but bring about other conditions of a most serious character. 
I have heretofore been very careful not to condemn the practice of 
spraying, but simply to call attention to the dangers accompanying the 
practice and particularly the excessive, even irrational, application of 
these poisonous preparations to the trees and eventually to the soil. If 
the soils themselves already contain arsenic enough to pass into the 
plant system it makes the application of more arsenic only the more ill- 
advised 1 . 
Up to the present time we do not know of any other practical 
and effective means of protecting our fruit against the codling moth 
than some form of arsenic, and ro far as we now see we must continue 
to use this means. This, however, does not mean that we cannot im¬ 
prove the practice in several ways. It has been demonstrated that 
a much smaller amount of arsenic may be used than has heretofore 
been customary, with most excellent results. Prof. Gillette showed 
several years ago, that 95 per cent, of the protection given to a crop 
when three or four sprayings were made was effected by the first 
spraying. His investigations have shown that a single spraying, 
thoroughly well done, will produce' clean apples unless there 
is some local source, an adjoining unsprayed orchard, from which moths 
may migrate and infest the orchard anew. There is another way of 
improving our practice, namely, by using a form of arsenic more insolu¬ 
ble in water than the forms now used and which will change but slowly 
into a soluble form in the soil. We have considerable reason for hop¬ 
ing that the sulfid of arsenic may be used with benefit in this direction. 
A still greater improvement would be to obtain some substance which 
would furnish our fruit the desired protection^ but which would be 
entirely free from the serious objections which apply to the use 
of any arsenical preparation. This is not an impossibility, as indicat¬ 
ed by the report of experiments with nicotine made by Prof. Gillette to 
the American Association of Economic Entomologists, at its recent 
meeting in Boston. 
The assumption that the arsenical preparations used for spraying 
are insoluble in water is not justified, and yet this is a condition which 
they must fulfill in order that thay may be safely used. Further condi¬ 
tions may, and in some cases certainly do, exist in the soil which makes 
them more soluble than they are in pure water. I have met with manv 
men to whom it was a matter of some surprise that the arsenic might 
accumulate in the soil, though they knew that they were spraying a 
number of times annually and that the amount of soluble arsenic in the 
soil might increase with the years. 
Bulletin 131 states that this line of work was a direct outgrowth 
of my attempt to study the alkalis of the state. It was then thought that 
it was rather more than probable that the abundance of these salts in 
some of our soils had produced an exaggerated effect of the arsenic 
on our trees. There may be some truth in this view but I am now of 
