MUSHROOM PESTS AND THEIR CONTROL 9 



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°. Recent experiments have shown that the ideal "heat" is 

 from 130° to 135° for 7 or 8 days, but the usual mushroom house has 

 not sufficient heating capacity to maintain this temperature after the 

 compost itself begins to cool. At temperatures above 120° 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 fumigants. 



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 loca- 

 tions 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 tem- 

 perature of the bottom beds will usually lag about 10° F. 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 frequently 

 the case in amateur mushroom culture, the quantity of manure is too 

 small and the insulation insufficient to allow the temperature 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 some- 

 times have a harmful effect on mushroom 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 tops 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 on 

 the floor along the center of the house, adjusted to direct the air cur- 

 rent upward at an angle of from 45° to 80°. Better results, however, 

 have been obtained by placing the fans on supports resting on 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 and run for 5 or 6 hours, 

 shut off to cool for 2 or 3 hours, and then run for another 5 or 6 hours. 



To keep a check on the conditions during the heating process, ac- 

 curate 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 con- 

 ducted, it seems fairly safe to state that an air temperature ranging 

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

 distributed through the room, will kill all insects and mites harm- 

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

 just above the floor are difficult to maintain, consequently fumigation 

 is necessary. The manure in the beds will reach a much higher tem- 

 perature during this time but should not be allowed to exceed 145°. 



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