24 



vator consisted of an iron rake 6 in. wide and i8 in. long, con- 

 structed of f and I in. iron tubing which was attached to a two 

 wheeled hand cultivator frame. The rake was provided with 7 teeth 

 of |- inch tubing 8 in. long, the lower ends of which were nearly 

 closed by flattening them out. Numerous small holes drilled 

 through the lower portion of each tube permitted the exit of steam. 

 Steam was connected with this apparatus through the top by means 

 of a hose attached to a small high pressure boiler and it passed 

 down through the perforated tubes into the soil with considerable 

 force. As the steam cultivator was passed slowly through the soil it 

 heated up the upper layers to the depth to which the teeth pene- 

 trated, which was about 4 to 6 inches. We found that b\ passing 

 this through the soil three or four times the temperature was raised 

 in some places as high as 194° F., and averaged about 168'' F. 

 throughout the bed. This temperature did not hold very long, how- 

 ever, and the corners and edges of the bed were difficult to reach. 

 The percentage of Drop with this treatment was 18% w'hile the 

 normal bed gave 19%, which equals a gain of 5%. The amount of 

 Rhizoctonia in the treated bed was 21% against 49% for the nor- 

 mal or untreated bed, or in other words, a gain of 57%. It appears 

 from this experiment that the Rhizoctonia does not require as high a 

 temperature for its extermination as the Drop. This method has 

 been given only one trial and while it is capable of reducing the 

 amount of Drop infection to a much greater extent than in this 

 experiment, we do not recommend its trial, or that of any other par- 

 tial control method, inasmuch as it would have to be used previous 

 to the setting out of every crop. 



Larger and deeper steam cultivators could be employed which 

 would do the work more effectually, but in every case the corners 

 and edges of the bed would be difficult to reach, and hence, without 

 care, these places would constitute a source of contamination. 



The hot water method showed better results than the preceding 

 one, it heated the soil to a depth of 4 in. at a temperature from 176° 

 F. to 186° F. (See a. Diagram VI.) The water was taken through 

 a hose from an adjacent pipe connected with the house system of 

 heating and was 210° F. as it left the hose. The top layer of the 

 soil was quite freely saturated with water. The percentage of Drop 

 was only 4.5% and there was present no Rhizoctonia or Bacterial Rot, 

 although the Botrytis Rot was present. Sterilization cannot be 



