104 Diseases of Truck Crops 



spotting of the caps, the severity of which differs with 

 the cultivated varieties, especially the large white 

 kinds. The spots, which do not extend deep into the 

 flesh, appear while the mushroom is in the but- 

 ton stage, or when the cap is fully expanded. The 

 spots are pale yellow, becoming a chocolate brown. 

 Though the disease does not seem to reduce the 

 yield, the market value of the spotted mushrooms 

 is considerably reduced. 



The Organism. Pseudomonas fluorescens is a 

 small rod rounded at both ends and motile by means 

 of polar flagella. It is a facultative anasrobe; pro- 

 duces no endospores, no gas, but liquifies gelatine. 

 On beef and potato agar it produces a shiny grayish 

 white growth accompanied by a greenish pigmenta- 

 tion, which diffuses in the substratum. 



Control. Spraying the mushroom caps with solu- 

 tions of benetol, sodium carbonate, or copper sul- 

 phate seems to have no beneficial effect. On the 

 other hand, fumigating the beds with sulphur before 

 planting the spawn insures the production later of a 

 clean crop of mushrooms. The amount of sulphur 

 to use is about one and a half pounds to each thou- 

 sand cubic feet of cave space. 



The Mycogone Disease 



Caused by Mycogone perniciosa Mag. 



The Mycogone is a very destructive mushroom 

 disease. The exact amount of its distribution in the 



