CONTROL OF BLACK-ROT AND STEM-ROT OF THE SWEET POTATO. 17 



handling with shovels or by placing it in boxes, etc., that have not 

 been disinfected. 



Some system patterned after the following plan is suggested by 

 Mr. W. W. Gilbert and, with such modifications as are necessary to 

 meet local conditions, may be found feasible. A stationary or port- 

 able engine must be available which can stand a pressure of 80 to 100 

 pounds of steam. If a stationary engine is used, the soil must be 

 hauled to the engine for sterilization. In such cases it will be found 

 convenient to construct a strong box which can be tightly covered, 

 sufficiently large to hold 1, H, or 2 tons or more of soil, with 1| to 2 

 inch perforated iron pipes (the perforations to be about three-six- 

 teenths of an inch in diameter and 6 inches apart on the under side) 

 laid in the bottom about 1 foot apart, which can be attached to the 

 engine by a pipe or steam hose. This is easy to accomplish by con- 

 necting the parallel rows of pipes in the box with a header having an 

 outlet connecting with the engine. This box should be loaded on a 

 wagon and hauled to the farm and filled; then brought to the engine 

 and sterilized and again returned. If there is any general demand 

 for soil sterilization, several completely equipped boxes will be 

 needed. The use of portable boxes is advisable merely to protect 

 against reinfestation of the soil after it is sterilized. 



It will be more convenient to have a stationary sterilizing box and 

 haul the soil to and from it in a wagon if the necessary care is taken 

 to wash out the wagon box with a formaldehyde solution before the 

 sterilized soil is again put in it. This method will save time, labor, 

 and expense. The soil can then be brought to the engine, scooped into 

 the box, spread out 8 or 10 inches deep over the pipes, sterilized, and 

 returned to the wagon. Practically the same methods can be em- 

 ployed if a portable engine is used to sterilize the soil on the farm. 



When the pressure is up to about the capacity of the engine, prob- 

 ably 80 to 100 pounds, the steam should be turned on by opening the 

 valve about half way. The higher the pressure the drier the steam. 

 The soil should be sterilized for about 40 minutes after the tempera- 

 ture reaches 100° C. (212° F.). The thermometer should be placed 

 in the soil midway between the pipes. 



If it is impracticable or impossible to sterilize with steam it may 

 be done by the use of a formaldehyde solution, 1 pint of formalde- 

 hyde (40 per cent) to 24 gallons of water. Formaldehyde is cheap 

 and can be purchased at almost any drug store. When the soil is to 

 be treated with a formaldehyde solution it should be placed in a tight 

 box or other receptacle and enough of the solution added to soak it 

 thoroughly. The application should be made at least two weeks be- 

 fore the soil is to be used, in order to allow the formaldehyde to 

 evaporate. An occasional stirring of the soil will assist in the escape 



[Cir. 114] 



