58 DISEASES OF ECONOMIC PLANTS 



ticularly Kentucky and other Southern States, the end in ' 

 view being the improvement of the tilth of the soil and the 

 killing of weed seeds rather than of any fungous diseases. 

 In Italy, as well, burning is now considered a part of the 

 regular method of tobacco seed-bed preparation, it having 

 been resorted to as a preventive of Thielaviose. 



Two methods of surface firing are in vogue; the first 

 by direct firing, the second requiring the use of a pan. In 

 the direct method, the land to be disinfected is first 

 thoroughly pulverized and manure applied. It is then 

 covered with straw, brush, and wood sufficient to make a 

 hot fire. This is ignited and allowed to burn an hour or 

 so. The ashes are raked into the surface soil, and the seed 

 is sown. 



The second method, pan firing, consists in the use of a 

 sheet-iron pan, 3 by 9 feet, under which a fire is made. 

 This is set in the middle of a 9-foot bed, and the soil on 

 one side to a depth of 6 inches is shoveled in and heated, 

 great care being taken to keep it moist, otherwise the 

 humus would be burned out and the physical texture irrepa- 

 rably altered. After an hour this soil is put back and 

 that from the other side of the pan subjected to the same 

 treatment, and then the pan moved along to a new place. 

 The soil underneath the pan itself is thereby subjected to 

 heat for two hours. 



Formalin disinfection. — The use of formalin for the 

 disinfection of greenhouse soil and of tobacco seed beds 

 against Rhizoctonia has been in vogue for some time with 

 excellent results. It furnishes a very simple means of 

 disinfection as follows : The beds are thoroughly prepared 

 as for the other methods of disinfection described and are 



