August, 1919 
WISCONSIN HORTICULTURE 
163 
oxide. The principal substances 
with which it is combined for 
spraying purposes is copper used 
in making Paris green, zinc in mak- 
ing arsenite of zinc, lead in making 
arsenate of lead, and calcium in 
making arsenate. These four poison 
sprays are the ones now mostly in 
use. A new material, arsenate of 
magnesium, has recently appeared 
on the market but we have had no 
opportunity to test its comparative 
value. 
Paris Green. Paris green in 
comparison with other insecticides 
has a higher arsenical content than 
the other materials and a greater 
killing efficiency but it is not an 
economical spray material at 60 to 
80c per pound and because of its 
tendency to cause foliage injury, 
we believe that arsenate of lead is 
a much more desirable spray to us*e. 
When Paris Green was first put 
on the market it combined 1% of 
free arsenic oxide but this is now 
greatly eliminated through present 
methods of manufacture and in 
time it is possible that a Paris 
Green can be manufactured that 
will not injure the foliage any more 
than the other arsenates. However, 
at the present time the percent of 
free arsenic oxide is so great as to 
cause much more burning than is 
generally realized by our growers. 
How and When to Use : If 
Paris green is to be used for the po- 
tato beetle, it should be pointed out 
to the grower that it is not neces- 
sary to use more than 114 to 2 
pounds to 50i gallons of water or 
per acre if stated in those terms. 
In cases where greater amounts are 
thought necessary, it is either due 
to poor application or to a poor 
grade of material. 
Arsenate of Lead. Without ques- 
tion this is the most desirable in- 
secticide on the market today and 
is now more generally used than 
any other poison insecticide. The 
reasons for this are that when pro- 
perly prepared, it is safe to use on 
the foliage of practically all plants 
and it stands well in suspension 
and sticks and spreads well on the 
foliage. It does not have quite the 
killing efficiency of Paris green hut 
we have found the difference to 
be small in cases where pure arse- 
nate of lead was used. It is neces- 
sary to point out that in our experi- 
ments, the so-called lead hydrogen 
and not the basic arsenate of lead 
was used. 
The insecticide manufacturers 
and chemists know arsenate of 
lead in two forms. In each one 
the arsenic forms a different com 
bination with the lead so that the 
one known as lead hydrogen, acid, 
or diplumbic arsenate of lead, 
there are two parts of lead and one 
part of arsenic oxide forming a 
material with 33% poison in it. The 
second form of arsenate of lead 
known as basic, neutral or triplum- 
bic arsenate of lead forms a com- 
bination in which one part of arse- 
nic oxide is combined with three 
parts of lead and in which 
the poison amounts to 25% of the 
total. 
The basic lead arsenate forms a 
much stronger combination be- 
tween the lead and arsenic than 
does the lead hydrogen arsenate of 
lead and is therefore a more stable 
spray. It does not break down as 
rapidly in the presence of water or 
air and is the most desirable spray 
to use on tender plants in certain 
climates. However, the very fact 
of its extreme stability makes it an 
undesirable spray against insects 
which do not seem to be quickly af- 
fected by poison. 
The lead hydrogen arsenate is a 
less stable product and is more 
easily broken up in contact with 
air. water or other chemicals a*d 
for this reason is a much quicker 
acting poison and has a higher 
killing efficiency than the basic 
form. This fact also makes it some- 
what more dangerous to use on the 
foliage of tender plants and under 
certain conditions, severe foliage 
injury is liable to occur. 
The present methods of manu- 
facture are such that the free ar- 
senic in either one of these mater- 
ials is limited to a minimum and 
in our experiments in Wisconsin 
we have found practically no in- 
jury resulting from the use of lead 
hydrogen arsenate and recommend 
its use entirely. The differences 
in the killing efficiency of these two 
materials probably accounts in a 
large measure for the unsatisfac- 
tory reports that have come in re- 
garding the use of arsenate of lead 
for the Colorado potato beetle. The 
basic or triplumbic form is so slow 
in its action that very poor results 
are obtained when used against 
this insect. On the other hand 
lead hydrogen arsenate in small 
amounts gives immediate and effici- 
ent results. It should also be noted 
that where the basic lead arsenate 
is used that while the insects 
which have fed on it do not die im- 
mediately, most of them become 
sick and do not feed. 
How and When to Use : This 
material comes in a paste or pow- 
dered form and in the paste form 
should be used just twice as strong 
as the powder. For Colorado po- 
tato beetle use 2 to 214 pounds of 
(Continued on page 167) 
WANTED— WORK 
Married man able and willing- to 
work wants work on dairy farm or 
market garden preferably where high- 
grade poultry is kept. 
City bred but seven years experi- 
ence on market garden. Wife willing 
to help in house or act as housekeeper. 
Address C. Wisconsin Horticulture. 
