234 
PARK AND 
CEMETERY. 
INSECT PESTS OF THE GREENHOUSE 
Address before the Floral Society of Minnesota, by 
William Moore, of the University of M nnesota Farm. 
The chief pests of the greenhouse which 
might be considered in this paper are scale 
insects, mealy bugs, the white fly, the green 
fly, the red spider, thrips, sow bugs and 
snails. These are, no doubt, generally 
known to florists, and although there are 
various species included under these dif- 
ferent groups, it is not necessary to go into 
the details of the species. 
The purpose of the talk here given is 
to be rather a brief discussion of some of 
the better methods of combating these 
various pests. The first to be considered 
might be the sow bugs and snails. The 
best measures to be adopted in the case of 
these is to prevent an attack by keeping 
the house well lighted, not allowing rub- 
bish to accumulate, and doing away with 
dark, damp places. In other words, a 
well-built, up-to-date greenhouse should be 
comparatively free from either of these 
pests. 
In this connection it might be noted that 
several florists claim to have obtained very 
good results by using sugar and paris 
green to destroy the sow bugs. This is 
laid on boards on the table and is said to 
be readily eaten by the sow bugs. These 
two pests, however, are of minor impor- 
tance. 
Probably the most universal pests of the 
greenhouse are the various species of green 
flies found therein. To these might be 
added species of thrips, since the treatment 
is the same for both. The best measure to 
adopt against these two pests is fumigating 
with tobacco. This fumigation is done by 
burning tobacco dust or tobacco ribs or 
some of the standard preparations put up 
for that purpose, such as nicofume paper. 
Tobacco should be always placed on the 
floor, as the fumes rise rapidly, and if 
placed on the level of the table would not 
have the opportunity of coming in contact 
with the plants in the same way as they 
otherwise would. 
There is one group of plants which can- 
not be fumigated by means of tobacco, and 
that is violets. Fumigation with tobacco 
will spot the leaves of violets and should 
never be done. 
This brings us to another treatment 
which is oftentimes used, almost universal- 
ly, for insect pests of the greenhouse, 
namely, fumigation with potassium cyanide. 
Unfortunately, a number of factors enter 
into the question as to whether the cyanide 
will kill the plants in the greenhouse or 
not. A number of experiments have been 
conducted by different people and many 
different results have been obtained, from 
which there seems to be some relationship 
between the temperature of the house and 
the burning of the leaves by the cyanide. 
The humidity is also another factor which 
must be considered, as it seems prob- 
able that the greater the humidity the 
c 
greater the chances are of the cyanide burn- 
ing the foliage of the plants. Another fac- 
tor which makes the fumigation of green- 
house plants difficult is the great variety of 
plants which may be in the infested house, 
since one plant can stand a strong dose 
of cyanide while another one will succumb 
to even a weak charge of cyanide. It must 
be remembered first that potassium cyanide 
and its gas are deadly poisonous, and the 
greatest care should be taken in handling 
it. Fumigation should be done during the 
night, as if it is done even on a cloudy 
day it is apt to burn the foliage of the 
plants. The plants should not be watered 
or sprinkled directly before fumigation, nor 
should water be standing about on the 
floor in puddles, although the floors may 
be slightly damp. 
To fumigate a house with cyanide it is 
necessary first to ascertain the number of 
cubic feet in the greenhouse. This is often- 
times neglected, with the result that the 
charge of cyanide used destroys many val- 
uable plants. Taking a cross section of 
the greenhouse which has both sides equal 
in height, we will letter the house A for 
the lower right-hand corner; B for the 
upper right-hand corner; C for the apex 
of the house ;‘D for the upper left corner, 
and E for the lower left corner. Due to 
the slanting roof, one cannot measure di- 
rectly the number of cubic feet. By multi- 
plying the height of side of house by the 
width of the house we will get the number 
of square feet in the portion of the house 
represented by A, B, D, E. Multiplying 
the number of square feet in this portion 
by the length of the house, we get the num- 
ber of cubic feet in the lower portion of 
the greenhouse. To obtain the number of 
cubic feet in the upper portion which has 
the slanting sides it is necessary to divide 
the section of the greenhouse into two 
right triangles, from the bottom of the 
house to the apex. The height from the 
bottom to the apex should be measured, 
and from this the height of the side should 
be subtracted. This will give us the height 
of the right triangle from C down to a 
point directly beneath it, which we will call 
F. This distance, multiplied by the dis- 
tance from D to F, will give the number of 
square feet in the two triangles CDF and 
B C F. This multiplied by the length of 
the greenhouse will give the number of 
cubic feet in that portion. The number 
of cubic feet in these two different por- 
tions is added together, making the number 
of cubic feet of space in the greenhouse. 
When one side of the greenhouse is 
higher than the other side, the method of 
obtaining the number of cubic feet is some- 
what more complicated. In such a case, 
let the lettering be the same as in the 
previous case, with the side A B higher 
than the side D E. In this case, we will 
have to measure the distance from E to a 
point H, which is at the floor directly un- 
derneath the apex of the house. This dis- 
tance multiplied by the height D E will 
give the number of square feet in the por- 
tion of the greenhouse D E H F. Multi- 
plying by the length will give the number 
of cubic feet in that portion of the green- 
house. Measuring then from A to H and 
multiplying A H and A B will give the 
number of square feet in the section 
A B G H. That multiplied by the length 
gives the cubic feet in that portion of the 
greenhouse. We now have two right tri- 
angles to get the number of square feet. 
We take the distance D F, which is the 
same as E H, and multiply that by the 
distance of C F, which is equal to the dif- 
ference between C H and D E. Dividing 
the product by 2 gives the number of 
square feet in the angle DCF. Multiply- 
ing this by the length gives the number of 
cubic feet in that portion. The portion 
C G, which is the difference between C H 
and A B, multiplied by B G, which is equal 
to A H, and dividing by 2 gives us the 
number of square feet in B C G, which is 
then multiplied by the length to give the 
number of cubic feet. The sum of the 
cubic feet in these four different portions 
gives the number of cubic feet in such a 
greenhouse. 
A greenhouse should always be meas- 
ured and the number of cubic feet care- 
fully worked out before fumigation is 
started. 
The material used in fumigation is po- 
tassiniu cyanide, sulphuric acid and water. 
In an earthenware crock is placed the de- 
sired quantity of water and to that is 
slowly added the sulphuric acid, stirring 
