Ss ‘BULLETIN 518, U. S. DEPARTMENT OF AGRICULTURE. 
VENTILATION AFTER FUMIGATION. 
If there is a light wind, a ventilation of 10 to 15 minutes, using side 
and top ventilation, will be sufficient and will not lower the house 
temperature to a dangerous point unless it is close to zero weather 
outside. If it is a still evening and the outside temperature is not 
below 32° F., a 20 to 30 minute ventilation is satisfactory. 
In case it is necessary to enter the house shortly after ventilation 
to determine the temperature, the person entering should not remain 
any longer than is necessary. 
EFFECTS OF WEATHER CONDITIONS ON FUMIGATION. 
TEMPERATURE. 
Much experimentation has proved that excessive heat and cold will 
affect the results of fumigation. In most instances it is not advisable 
to fumigate if the temperature in the frame exceeds 70° F., or if 
the temperature is less than 55° F. It is possible that a variation of 
five degrees from the latter temperature will not result in serious 
injury to the plants, providing, of course, that the plants are not 
affected by such a low temperature. 
LIGHT. 
Light unquestionably affects fumigation. It has been known for a 
long time that it is very undesirable to fumigate when the sun is 
high. Furthermore, recent experiments have demonstrated that 
some injury may result to plants which have been subjected to fumes 
if, on the following day, the sun is very bright. 
MOISTURE. 
The question of moisture has received considerable attention from 
various fumigators, and it appears to be the consensus of opinion 
that excessive moisture in the presence of the gas does not increase 
the injury to plants and plant products under fumigation. A large 
number of plants have been fumigated in boxes immediately after 
syringing, when the leaves were covered with a film of water, with 
apparently no injury to the plants, and the insects on the plants were 
successfully controlled, which corroborates the experience of Morrill, 
Quaintance,? and Woglum.? 
Hydrocyanic-acid gas is readily soluble in water, and as a result 
the presence of excessive moisture in greenhouses decreases the ef- 
fectiveness of the gas and consequently lessens the possibility of in- 
jury to the plants by burning. Fumigation experiments have been 
1 Bul. 76, Bur. Ent., U. S. Dept. Agr., p. 12, 1908. 
2Bul. 84, Bur. Ent., U. S. Dept. Agr., p. 24, 31, 1909. 
3 Bul. 90, Bur. Ent., U. S. Dept. Agr., p. 68, 1912. 
