24 CIRCULAR 251, U. S. DEPARTMENT OF AGRICULTURE 



spores. If an open well is used it may be necessary to disinfect it 

 occasionally. There is little chance for Mycogone to be spread in 

 bottle spawn that has been made under aseptic conditions. 



Mycogone is killed by long exposure to moderately high tempera- 

 tures. All the evidence at hand indicates that a temperature of 120° 

 F. for 48 hours in a mushroom house will eradicate the fungus from 

 the house, and the manure in a house which has been through a good 

 heat should be free from Mycogone. This and other circumstantial 

 evidence indicates that most severe outbreaks of bubbles in commer- 

 cial houses are due to carelessness in disinfecting the house or to 

 infested casing soil. 



Losses from infested casing soil can be eliminated by taking 

 precautions to prevent the contamination of the soil. To determine 





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Figure 14. — Mushrooms distorted by the bubbles or Mycogone 



whether soil is contaminated, small test beds may be cased with soil 

 samples taken from fields that are to be used as sources of soil for 

 subsequent crops. If soil infestation becomes general and there is 

 no Mycogone-free soil available, the fungus can be eradicated by 

 heating the soil to at least 120° F. for 48 hours. This can be done 

 in specially equipped rooms, or by placing the soil in tra}^s near the 

 top of the house during the heat, if the heating plant is large enough 

 to raise the temperature artificially in the event that the manure 

 does not generate sufficient heat. When the soil is heated to more 

 than 150°, Mycogone spores are killed in less than an hour. Some 

 growers find partial sterilization with live steam, as described in 

 Farmers' Bulletin 1629, quite satisfactory. Others complain of a 

 loss of water-holding capacity and molding of the steamed soil. The 



