8 BULLETIN 513, U. S. DEPAETMENT OF AGEICULTUEE. 



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 coiisensus 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 Avith 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 Bui. 76, Bur. Ent., U. S. Dept. Agr„ p. 12, 1908. 



2 Bui. 84, Bur. Ent, U. S. Dept. Agr., p. 24, 31, 1909. 



3 Bui. 90, Bur. Ent, U. S. Dept Agr., p. 68, 1912. 



