MUSHROOM GROWING IX THE UNITED STATES 25 



injurious effect of steaming apparently varies with different types of 

 soil and in many cases is temporary and can be eliminated by steam- 

 ing some time prior to casing, or by aeration of the steamed soil. 



After the disease has become established in a house strict sanitary 

 measures are necessary to prevent workmen from spreading it. The 

 loss may be reduced somewhat by growing the crop around 50°. 



The measures outlined above apply particularly to the prevention 

 of the disease in conventional mushroom houses, but the principles 

 may be applied to most situations. 



BACTERIAL SPOT 



The spot disease of mushrooms caused by Bacterium tolaasi 

 (Paine) Elliott and other soil organisms is found wherever mush- 

 rooms are grown commercially. It is the most troublesome disease 

 in caves and is often quite serious in standard houses, especially 

 toward the end of a crop period or in growing summer crops in 

 artificially cooled houses. It is characterized by brown, almost black, 

 spots over the surface of the mushroom cap. These spots are often 

 covered with a bacterial ooze. Usually they do not penetrate deeply 

 into the mushroom flesh, but at times the bacteria follow along the 

 tunnels of fly larvae and blacken the entire stem and parts of the cap. 

 Infection is known to be favored by high humidity and prolonged 

 wetting of the mushroom caps while watering the beds. Circum- 

 stantial evidence indicates that the inoculum comes principally from 

 the soil. Growers should endeavor to avoid spattering water from 

 the soil on to the mushrooms, take every precaution to prevent the 

 house from becoming too damp, and, weather permitting, attempt 

 to dry off the mushrooms rapidly after watering by opening the 

 doors and ventilators for a few minutes. Mushrooms on old beds 

 seem to be more subject to spotting than do new breaks and at times 

 poor ventilation seems to be an aggravating factor. 



OTHER DISEASES 



The " green mold " disease spreads in patches from the masses of 

 mushroom tissue which are sometimes left in the soil after picking. 

 Once a patch of the fungus causing this disease becomes established 

 in the soil, more button mushrooms are rarely formed in that area. 

 Its development can be retarded by removing all of the solid fungus 

 tissue at the base of the mushrooms when picking them, and filling 

 the holes with fresh soil. Excessive dampness should also be avoided. 

 Liming seems to be somewhat beneficial as a preventive but not as a 

 control measure. 



The presence on the bed of a large proportion of deformed mush- 

 rooms with superfluous gills over the upper surface of the cap 

 resembling the rose comb of poultry and sometimes deeply seamed 

 and cracked has been traced in many cases to mineral oil or oil 

 products. In some cases abnormalities were apparently due to the 

 use of kerosene in smudges, disinfectants, and insect^ sprays. In 

 others they were due to accidental contamination of the water-supply 

 with oil or grease. 



Among the diseases caused by competitive fun^i in the mushroom 

 bed the white plaster mold (sometimes called " flour mold ") and 

 truffles are the most troublesome. The former is caused by a fungus, 



