g CIRCULAR 457, U. S. DEPT. OF AGRICULTURE 



related pests, as well as being necessary to "sweat out" the manure 

 and put it in the best condition for the spawn to "run." An ideal 

 condition is to have the bottom beds at a temperature above 120° F. 

 and the top beds below 140°. At these temperatures all forms of 

 insect and mite pests will either be killed or driven to the surface 

 of the beds, where they can be reached with f umigants. 



Since ground beds are very difficult to heat properly, the insect 

 and mite pests contained therein cannot be driven to the surface 

 or killed by heat, and, since the fumigants in use at present do not 

 penetrate the compost more than an inch or so, the pests present 

 in such locations will survive and reinfest the house. Consequently, 

 if the ground beds cannot be raised 4 or 6 inches from the floor to 

 allow circulation of heated air beneath, it is better to abandon them 

 entirely. The temperature of the bottom beds will usually lag about 

 10° behind that of the top ones, and air temperature will usually 

 be 15° or 20° less on the floor than under the ceiling. 



If the weather is very cool at the time of filling, or, as is fre- 

 quently the case in amateur mushroom culture, the quantity of 

 manure is too small and the insulation insufficient to allow the tem- 

 perature to rise, the house may be heated artificially. Where steam 

 or hot -water heat is not available, kerosene or oil burners have been 

 used with success, but the use of oil heaters should usually be 

 avoided, as oil fumes sometimes have a harmful effect upon mush- 

 room growth. Care must be taken that the beds do not dry out too 

 much while this is being done. 



Because the lower beds are filled first and lose much of their latent 

 heat, and also because the warm air naturally rises to the top of 

 the house, the top beds heat faster and attain a higher temperature 

 than the bottom ones. A more even distribution of heat may be 

 obtained by the use of some method of forced air circulation. Where 

 electric current is available the best method is to place two or three 

 16-inch electric fans in the central alleyway. Most growers place 

 the fans upon the floor of the house along the center of the house, 

 adjusted in such a manner that the air current is directed up- 

 ward at an angle of from 45° to 80°. Better results, however, have 

 been obtained by placing the fans on supports resting upon the top 

 beds, with the air current directed straight down. By this means 

 the heated air in the top of the house is driven to the floor and is 

 forced to circulate over the bottom beds before again rising to the 

 top of the house. When the top beds have reached a temperature 

 ranging from 120° to 130° F. the fans should be started, run for 

 5 or 6 hours, shut off to cool for 2 or 3 hours, and then run for an- 

 other 5 or 6 hours. 



To keep a check upon the conditions during the heating process, 

 accurate thermometers should be inserted into the top and bottom 

 beds and hung in the central alleyway at the top and bottom of the 

 house. Judging from preliminary results of experiments now being 

 conducted, it seems fairly safe to state that an air temperature rang- 

 ing from 120° to 125° F., if maintained for a few hours, and if evenly 

 distributed through the room, will kill all insects and mites harmful 

 to mushrooms. Such temperatures on the floor of the house and 

 just above the floor are difficult to maintain, consequently fumiga- 



