74 HATCH EXPERIMENT STATION. [Jan. 



Sterilization of Soil in Greenhouses for Fungous 



Diseases. 



This method of treating soil infected with disease-pro- 

 ducing organisms or germs has been frequently dealt with in 

 the publications of this division and elsewhere. We have 

 recommended this method for the extermination of such 

 fungous pests in the soil as cause the drop in lettuce and 

 other plants, the timber rot in cucumbers, the Rhizoctonia 

 and damping fungus (Pythium De Baryanum), and in part 

 the stem rot in carnations. It has also been recommended 

 for nematode worms, diseases caused by Heterodera, which 

 aftect indoor cucumbers, tomatoes, roses, violets, cyclamens, 

 muskmelons and other greenhouse plants, and for the aphis 

 and red spider. It is also effective in the destruction of weed 

 seeds. One lettuce grower maintained that it paid to steril- 

 ize soil for this purpose alone. Heating of the soil greatly 

 accelerates the growth of plants, and when this method of 

 treatment is applied to lettuce houses afi'ected with the drop 

 and RJiizoctonia ;, it successfully eliminates these diseases, 

 which are all a skilful grower needs concern himself about. 

 This method of treatment has not been recommended for 

 such diseases as top-burn, mildew of lettuce, nor for the 

 damping fungus (Botrytis) in propagating pits, or for any 

 other fungi giving rise to diseases which are freely dissem- 

 inated by spores. Neither does this method, as ordinarily 

 applied, succeed in accomplishing absolute sterilization of 

 the soil. It is merely a sort of pasteurization. Cultures 

 of the soil heated to 212° F. for a short time wonld show 

 numerous bacteria, and nryriads of others subsequently 

 come in from the air and through the water applied to the 

 soil. 



The last year has seen quite remarkable strides made in 

 the practice of methods of ridding the soil of parasitic organ- 

 isms by means of heat. On account of the extensive use 

 of the sterilization method on a large scale by the most 

 efficient and practical gardeners, the process has been made 

 very much cheaper, and hastened to a large degree. At the 

 present time whole ranges of greenhouses owned by single 



