METHOD OF PREVENTING DAMPING OFF 193 



edges sunk their full depth into the soil, and weighted down with at 

 least 500 pounds of scrap iron. 



The steam was conducted through a one-inch pipe leading from 

 a steam tractor and introduced under the edge of the steaming pan. 

 Loose soil was banked and firmed along the outer edges of the 

 steaming pan to prevent the escape of steam. A pressure of at least 

 120 pounds of steam was developed before it was turned into the 

 steaming pan and the pressure in the engine gauge was maintained 

 above 100 pounds during the entire period of steaming. The amount 

 of steam admitted into the steaming pan was gauged by the rate at 

 which the soil took it up, the absorption during the early part of the 

 treatment being much faster than during the latter part. The pressure 

 in the boiler was maintained above 100 pounds in order to keep the 

 temperature at the necessary points. 



From 35 to 45 minutes' steaming with a pressure of from 120 to 

 160 pounds in the boiler has given entirely satisfactory results. Under 

 such treatment a temperature of from 94 to 98 degrees Centigrade was 

 secured to a depth of 8 inches in the seedbeds. Such treatment has 

 held in check the damping off of all species of conifers excepting the 

 Engelmann spruce, which has shown little or no benefit from the 

 treatment. 



COST OF STERILIZING 



The steaming pan cost $35.25, but with reasonable care it should 

 be serviceable for five years or longer. During the spring of 1916, six- 

 teen seedbeds were sterilized, at a cost of $33.45, itemized as follows : 



1/5 cost of steaming pan $7 . 05 



16 hours hire of engineer and engine 16 . 00 



16 hours hire of one laborer at .20 3 . 20 



16 hours hire of two laborers at .22^ ' • ^^ 



S33.45 



This gives a total cost of $2.09 per bed, which is a reasonable esti- 

 mate of the cost of weeding an untreated bed throughout the first 

 season. In the fall of 1916, twenty-three beds were steamed at a 

 total cost of $39, no allowance being made for deterioration of the 

 steaming pan. 



Four men are required to make an efficient crew, namely, an en- 

 gineer to fire the engine and keep up the steam, and three laborers to 

 spade up the seedbeds, shift the pan, and attend it during the steaming 



