12 CIRCULAR 4 5 7. V. 5. DEPARTMENT OF AGRICULTURE 



usually well outside the door before the first charge begins to gener- 

 ate gas. The doors should be closed and sealed at once. 



As an extra precaution, a house that has been fumigated should 

 not be entered, even by a person wearing a gas mask, until it has been 

 thoroughly ventilated. Fumigation with hydrocyanic acid gas should 

 be avoided during periods of cold weather, in order that the house, 

 may be properly ventilated after the fumigation without possible in- 

 jury to the crop because of a rapid drop in temperature during the 

 ventilation. 



As the floor is always the coolest part of a house that is heating or 

 at peak heat, it is here that insects and mites are most likely to sur- 

 vive the heat. "With any method of fumigation it is therefore desir- 

 able that as much of the gas as possible be kept in the lower part of 

 the house. Unless fans are kept running in the house at the time of 

 fumigation, the gas. being hot as well as lighter than air. will rise to 

 the top of the house. The best results have been obtained, by raising 

 the fans to the level of the fourth or fifth beds, about 5 or 6 feet or 

 more from the floor. In the pot method the air blast from the fans 

 should be directed straight down over each generator. This causes 

 the gas to blow along the floor and between the lower beds. After 20 

 or 25 minutes the concentration becomes nearly uniform throughout 

 the house, but for the first 20 minutes most of the gas is along the 

 floor, where it is most needed. Unless fans are of the fully enclosed 

 type, it is better to wait for about 10 minutes before turning them 

 on. as there is a remote possibility of gas and air forming an explo- 

 sive mixture which might be set oil by a spark. In experimental 

 fumigation of commercial mushroom houses it was demonstrated, by 

 using chemically equivalent dosages of calcium cyanide and sodium 

 cyanide with acid il:! 1 ^". 2).- that sodium cyanide and acid was 

 much superior to calcium cyanide in the concentration of gas obtained 

 and was about half as expensive per fumigation. 



There are two or three types of generators using sodium cyanide 

 and acid which, if properly used, are almost if not quite as effective 

 as the pots, and have the additional advantage that the gas is gener- 

 ated outside the building and forced in. the operator being at all times 

 in the open air. 



Sodium cyanide is extremely poisonous, and great care should 

 be exercised in handling it. It should be stored under lock and 

 key where it is not accessible to children or careless persons. 

 The same precautionary measures should be taken with the acid. 



The same rules as to procedure and safety apply to fumigation at 

 peak heat in cellars or other small spaces as apply during preparation 

 for the crop. Hydrocyanic acid gas should not be used in or adjacent 

 to dwellings at all. and sulfur only when there is no possibility of 

 the fumes escaping. In these places it is better to depend on heat 

 for rnushrooni-pest control at any time when the beds do not contain 

 spawn. 



GENERAL SANITARY MEASURES 



After the house has been through the "heat" and has been properly 

 fumigated, precaution should be taken to prevent reinfestation by in- 

 sects and the other closely related pests already mentioned. Doors 



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