MUSHROOM GROWING IN THE UNITED STATES 23 



is usually placed in pails or tubs along the alley and vaporized by 

 adding crystals of potassium permanganate at the rate of 1 pound 

 per quart of formalin. As in fumigating with sulphur, all prepara- 

 tions for quickly leaving and closing the house should be made before 

 the gas is released and exposed lights should not be used in the house, 

 since formaldehyde gas is explosive under certain conditions. 



While the crop is being picked all mushrooms affected with bubbles 

 should be carefully removed from the house and burned to prevent 

 the spread of the disease. After doing this work the men should 

 thoroughly disinfect their hands. It is also advisable to burn all 

 mushroom refuse. After each crop all traces of spent manure should 

 be removed and disposed of so that none will be used on fields near 

 the mushroom house or where it can possibly contaminate prospective 

 casing soil. 



The water supply also should be carefully guarded against con- 

 tamination with fungus spores or any traces of grease or oil which 

 might cause diseased or deformed mushrooms. 



For general disinfecting around the packing house, or disinfecting 

 workmen's hands or diseased areas on a bed, commercial prepara- 

 tions having carbolic acid, creosote, hypochlorite, or mercury as 

 active ingredients are widely used. 



DISEASES 



There are three general classes of mushroom diseases: Those 

 caused bj parasitic fungi or bacteria; those caused by fungi which 

 make conditions unfavorable for the mushroom by growing like 

 weeds in the bed; and those that cause malformation of the mush- 

 room apparently stimulated by nonliving irritants. The bubbles and 

 spot are examples of the parasitic class, plaster mold and truffles are 

 examples of the weed type, and rose comb is an example of the irri- 

 tant type. Certain of the more important of these are described on 

 the following pages. 



BUBBLES 



Bubbles is the most destructive disease of cultivated mushrooms. 

 It is caused by the fungus Mycogone perndeiosa Magn. which grows 

 into the mushroom and transforms it into a distorted, putrid mass. 

 (Fig. 14.) Soon after the mushroom is attacked the parasite pro- 

 duces a layer of white or brown spores over the surface. These 

 spores may be spread by various agencies and are able to live through 

 a long rest period under unfavorable conditions. The recurrence or 

 accumulation of the disease from one crop to another indicates that 

 the fungus either is remaining alive inside the house from one crop 

 to another or is being carried into the house during one of the cul- 

 tural operations. There are several possible methods of introducing 

 the fungus into the house — in the air or on insects entering through 

 doors or ventilators, or in the water, spawn, compost, or soil, or on 

 the clothing or hands of workmen. 



If the house is thoroughly disinfected with either sulphur or for- 

 maldehyde there is practically no chance for inoculum to remain in 

 the house from one crop to another. Likewise, disinfection of the 

 area surrounding the house and sanitary disposal of mushroom refuse 

 will materially reduce the danger from wind-blown or insect-carried 



