GEEENIIOUSE FUMIGATION WITH HYDKOCYANIC-ACID GAS. 9 



The residue loft iii the generators after fumigation should be 

 buried or poui'ed into a sink and the generator washed before being 

 stored for future operations. 



NUMBER OF GENERATORS TO BE EMPLOYED, 



The number of generators to be employed will depend largely upon 

 the size of the greenhouse, and they should be so arranged that the 

 gas will be distributed uniformly throughout the inclosure. To secure 

 this advantage a number of generator should bo used rather than 

 one large generator. Generators should be spaced from 20 to 25 

 feet apart (see fig. 4), and in case of a light wind a few extra gen- 

 erators should be placed on the windward side of the greenhouse. 

 An omice to each jar is as small a dose as is practicable, rniless the 

 generators are well rounded inside at the base or well tilted. 



EXPOSURES. 



Short exposui'es with a greater strength of gas are more satisfactory 

 than a weaker strength of gas overnight. In fact, better results will 

 be gained if the exposures do not exceed one to two hours. An 

 exposure of one hour is satisfactory in most instances. Short ex- 

 posures also have the additional advantage of permitting the green- 

 house to become thoroughly aired previous to the rising of the smi. 



VENTILATION AFTER FUMIGATION. 



If there is a light wmd, a ventilation of 10 to 15 mmutes, usmg side 

 and top ventilation, will be sufficient and will not lower the green- 

 house temperature to a dangerous pomt miless it is close to zero 

 weather outside. If it is a still evenmg and the outside temperature 

 is not below 32° F., a 20 to 30 minute ventilation will be satisfactory. 



In case it is necessary to enter the greenhouse shortly after ventila- 

 tion to determine the temperature, the person entering should not 

 remain any longer than is necessary. 



EFFECTS OF WEATHER AND OTHER CONDITIONS ON FUMIGATION. 



TEMPERATURE. 



It is not advisable to fumigate if the temperatm'e in the green- 

 house exceeds 70° F. or if the temperature is less than 52° F. 



LIGHT. 



Light unquestionably affects fumigation. It has been known for 

 a long time that it is very unsafe to fumigate when the sun is 

 high. Furthermore, some injmy may result to plants which have 

 been subjected to fumes if, on the following day, the sun is very 

 bright. 



MOISTURE. 



Hydrocyanic-acid gas is readily soluble m water, and as a result 

 the presence of excessive moisture in greenhouses decreases the 

 5601°— 17— Bull. 880 2 



