February, ’23] 
SASSCER & WEIGEL: GREENHOUSE FUMIGATION 
85 
salvia, etc., and the insects were practically eliminated except mealy bugs and these 
greatly reduced by the killing of immature larvae. Results are also given for the 
fern scale, the camphor scale and the Florida red scale. 
In a preliminary report 1 some data on the subject of fumigating 
greenhouses with hydrocyanic-acid gas on a commercial basis was pre¬ 
sented. The purpose of this paper is to give additional data on the 
same subject based on experiments conducted during the current year. 
The following formula was used in all of the tests: For each ounce avoirdu¬ 
pois of sodium cyanid (containing approximately 51% cyanogen), 1}4 
liquid ounces of sulphuric acid (1.83 specific gravity) and 3 fluid ounces 
of water were used. This is a slight divergence from the 1-1)4 —2 formula 
which has been generally accepted owing to the necessity of securing 
sufficient dilute acid to submerge the cyanid. Under greenhouse con¬ 
ditions, it is necessary to use a number of generators in order to secure 
an equal distribution of gas, and as this number is increased, the amount 
of chemicals in each generator is proportionately decreased, which will 
result in poor generation unless there is a slight excess of water. If it 
were possible to have a number of small generators considerably con¬ 
stricted at the bottom it would be possible to get a satisfactory genera¬ 
tion with the 1-1 ^-2 formula. 
Experiment i 
It appeared advisable to determine whether a greenhouse could be 
kept free from infestation of the common insects, as white flies, aphids, 
mealybugs, greenhouse Orthezia, etc., by subjecting the plants thereof 
to frequent one hour exposures of the gas at weak concentrations. An 
opportunity to conduct such an experiment presented itself during the 
early part of this year in a fairly tight propagating house of the United 
States Botanic Gardens, containing approximately 43,000 cubic feet of 
air space. The plants growing in this house represented 68 genera or 
about 120 varieties of the more common herbaceous and flowering plants, 
most of which were in S" pots or rooted directly in the propagating 
benches. The plants were obtained mostly from cuttings taken late 
in the season from plants grown out-doors during the summer, and in 
most cases were quite heavily infested with common mealybugs, green¬ 
house Orthezia, ants, and other hot house insects, when the experiment 
was undertaken. The first and second exposures were at the rate of y 
ounce and % ounce of sodium cyanid per 1,000 cubic feet of space re¬ 
spectively, while in each of the last five exposures ounce per 1,000 
*E. R. Sasscer and C. A. Weigel, Jour. Econ. Ent. June 1922, Vol. 15, No. 3, pp. 
200-204. 
