28 CIRCULAR 2 51, U. S. DEPARTMENT OF AGRICULTURE 



whether it would cause a great amount of damage in the modern east- 

 ern houses, since they provide atmospheric conditions unfavorable to 

 the insects' rapid development and reproduction. 



PREVENTION AND CONTROL 



Because the mushroom mycelium, as well as the mushroom itself, is 

 extremely sensitive to most fumigants, it is necessary to take certain 

 precautionary measures before placing the spawn in the beds, in 

 order to prevent heavy infestations by insect pests and subsequent 

 damage. 



In the course of the heat in the beds the temperature will rise high 

 enough, if forced air circulation is employed, to either kill the insects 

 in the compost or drive them to the surface where fumigants can be 

 used effectively. Electric fans provide the necessary forced circula- 

 tion of air during the heat. 



Two 16-inch fans will equalize the air temperature all over the 

 house and make the temperature in the compost fairly even in all the 

 beds. The various pests can then be killed by fumigation while the 

 temperatures are highest. 



Calcium cyanide, scattered on the floor in the alleyways at the 

 rate of 1 pound per 1,000 cubic feet of air space has heretofore been 

 most widely used, but the burning of sulphur, which is cheap and has 

 a double role as a fungicide and insecticide, is gradually replacing 

 the use of cyanide. Burning sulphur at the rate of 2 pounds per 

 1,000 cubic feet of air space while the compost is at its greatest heat 

 in the beds, and leaving the house closed for five hours after all the 

 sulphur has burned, has proven very effective against any pests in the 

 house at the time. Results of yield tests indicate that this process 

 has not injured the compost for subsequent mushroom culture. 



Results of hydrogen-ion determinations have shown conclusively 

 that the sulphur fumes do not penetrate much more than 1 inch into 

 the uncased compost and that the surface compost is rendered 

 slightly more acid than it was before being fumigated. Hydrocyanic 

 acid gas penetrates the compost to the same depth. 



To prevent possible infestation of the houses after the compost 

 has gone through its heat and has been fumigated, the doors and 

 ventilators should be screened with 30-mesh copper-wire cloth. To 

 prevent rapid development and multiplication of insects and mites 

 the temperature of the house should not go above 55° F. while 

 cropping. 



A dust consisting of 60 per cent pyrethrum powder and 40 per cent 

 finely ground clay, used at the rate of 2y 2 ounces per 1,000 cubic feet 

 of air space, has proven very satisfactory for control of the adult 

 flies and does not injure the mushrooms. 



HARVESTING, PACKING, AND MARKETING 



Comparatively little skill is required in picking mushrooms. They 

 are usually gathered at a stage of growth about 12 hours before the 

 veil would normally rupture. Mushrooms in the same stage of 

 growth often range from 1 inch to 3 inches in diameter, so the prin- 

 cipal consideration is not the size of the mushroom but whether it has 

 finished growing in the closed form. Mushrooms are pulled rather 



