5 o8 
Journal of Agricultural Research 
Vol. XXIV, No. 6 
Cooley (j) reports its use on the foliage of potato and cabbage without 
injury. Johnston {13) reports the use of zinc arsenite in the propor¬ 
tions of I, and 2 pounds to 50 gallons of water on potatoes, without 
foliage injury. Clinton and Britton {2) report two applications of zinc 
arsenite on apple trees at intervals of seven days, using pound to 50 
gallons, with foliage injury so severe that the trees dropped many of their 
leaves. Volck {34) recommends the substitution of zinc arsenite for lead 
arsenate for the &st two sprayings, i. e., full bloom and 10 days later, 
but in the following combination: Zinc arsenite (dry basis), 6 pounds; 
iron sulphid, 6 pounds; Black leaf 40, i pound; water, 200 gallons; 
because when iron sulphid is added, the foliage-injuring properties are 
largely restrained. If used alone, only the first (full bloom) spraying 
should be applied. For later sprayings arsenate of lead is recommended, 
Melander (19) says “It [zinc arsenite] is easy to use, adhesive, and 
has not scor<±ed in our tests [on apple],” Schoene {24) found that on 
apples zinc arsenite alone or in combination with soap, glucose, or lime 
sulphur caused more or less injury, but that lime or Bordeaux prevented 
this injury. In other experiments with zinc arsenite, slight injury 
occurred on the foliage of pear and plums, peach and grape leaves were 
severely scorched, while potatoes and cabbage were uninjured. It 
is also suggested in this bulletin that the solvent action of carbonic acid 
is partly responsible for the damage, Scott and Siegler {23) record 
injury to foliage of apple when zinc arsenite was used alone at the rate 
of % pound to 50 gallons of water or combined with milk of lime or with 
lime sulphur; that it caused moderate burning on bean foliage, except 
where lime was added, in which case no burning resulted; tiiat when 
added to slaking lime for Bordeaux mixture it caused no foliage injury 
to either apple or grape; and they suggested its possible use with Bor¬ 
deaux mixture in certain sections for the control of codling moth, bitter 
rot, and blotch. 
By various workers zinc arsenite is considered an effective insecticide 
against insects that are rather resistant to the poisoning effect of arsenic, 
such as larvae of webworm, tussock moth, etc. 
IkCeXHODS OF investigation 
It has been apparent for some time that there are several factors that 
influence the injury of foliage by arsenical compounds. Some of these 
are inherent in the plants themselves, some are dependent upon the 
chemical nature and solubility of the compounds used, while still others 
are to be classed as environmental conditions. It is obvious that to 
determine the relative importance of these several factors one of them 
must be varied while the others are kept as nearly constant as possible, 
for it is quite impossible to eliminate all but one. 
methods op appeying chemicals 
A large part of the spraying was done in the college orchard at Boze¬ 
man, Mont.; but this was quite extensively supplemented by orchard 
work in other parts of the State, and by spraying plants of various kinds 
in field plots, on the college campus, and in the botanical greenhouse. 
The mixtures were applied with a bucket spray pump under good 
pressure, using a Bordeaux nozzle. In the case of small plants, su^ as 
potatoes, sugar beets, etc., entire plants were sprayed, but on orchard 
trees this was rendered impossible by the very large number of applications 
