10 CIRCULAR 4 5 7, U. S. DEPARTMENT OF AGRICULTURE 



A temperature of 120° for 48 hours will eradicate the "bubble" dis- 

 ease (mycogone) also. 



During the heating of the compost in the beds much moisture is 

 driven off. In basements of dwellings it is inadvisable to try to reach 

 a high temperature unless the room can be sealed tightly enough to 

 prevent the moisture and heat from warping the floor above. 



Fumigation 



When the temperature of the beds has reached its maximum the 

 house should be fumigated with either sulfur or cyanide. 



SULFUR 



Sulfur should be burned at the rate of iy 2 to 2 pounds per 1,000 

 cubic feet of air space. The amount used per 1,000 cubic feet, how- 

 ever, should not exceed 2 pounds. Within 5 or 6 hours after the 

 sulfur has finished burning, the ventilators should be opened, the 

 house allowed to air out, and then closed again to prevent too rapid 

 cooling. Owing to the slow rate of burning and the rapid absorption 

 of gas by the moisture in the house, it is doubtful whether an efficient 

 fumigation is ever attained by burning sulfur in pans within the 

 house at peak heat. The outside burner previously described (p. 6) 

 will give much better results. 



Sulfur fumigation has a tendency to raise the acidity of the first 

 one-half inch or so of the beds (the limit of penetration of the gas), 

 and a green mold often follows. This soon disappears, however, and 

 neither it nor the increased acidity of the surface of the beds seems 

 to have any harmful effect upon subsequent mushroom growth. 



When a house to be fumigated is immediately adjacent to another 

 in production, every precaution should be taken to keep the fumes from 

 reaching and damaging the growing mushrooms. The ventilators of 

 the house in bearing should be open, and the house in heat should be 

 fumigated only when there is no wind, or when the wind is blowing 

 away from the house in bearing. In case of a double house, the other 

 half of which is in bearing or spawned, it is better to use cyanide 

 rather than to risk damage from sulfur fumes. 



HYDROCYANIC ACID GAS 



The materials in common use for hydrocyanic acid gas fumigation 

 are (1) calcium cyanide, (2) sodium cyanide and sulfuric acid, and 

 (3) liquid hydrocyanic acid. 



Since the application of liquid hydrocyanic acid requires special 

 equipment, as well as special training on the part of the operator, and 

 since it gives little better results than sodium cyanide and acid, it 

 may be left out of this discussion. 



The use of granular calcium cyanide at the rate of 1 pound per 

 1,000 cubic feet of air space is at present the most common method for 

 fumigating mushroom houses at peak heat. As hydrocyanic acid 

 gas is readily absorbed by moisture, the house, although damp, should 

 not be wet, with puddles of water standing in the alleyways, or much 

 of the gas will be lost before it is fairly liberated. Experiments have 

 shown that the maximum concentration of gas is reached in from 



