INSECT ENEMIES OF WESTERN FORESTS 



237 



.. 



Figure 109. — Burning in decks is an economical method of treating bark- 

 beetle-infested trees of small diameter. 



evenly and without too quick a flash. An explosive oil burns too 

 quickly to give good heat penetration. For burning standing trees 

 a light oil of gravity 32° to 34° Baume and a flash point of 

 160° F. has given the best results. For burning trees on the 

 ground ordinary fuel oil with a gravity of 27'°+ Baume and a 

 flash point of 225° F. has been found most satisfactory because of 

 its slower burning, greater heat penetration, and lower cost. In 

 either case from y 2 to % gallon is required to burn the average 

 lodgepole pine. The oil is applied with a hand pump through a 

 long nozzle. 



With the burning-standing method, the oil is sprayed as high 

 on the bole of the tree as the equipment will permit, about 30 feet 

 at present, and the entire top of the tree is "crowned out" with 

 fire (fig. 110). The treatment is effective only to the height of the 

 burn, and unless the bole is thoroughly scorched as high as to a 6- 

 or 8-inch diameter, which is usually the upper limit of infestation, 

 the tree must be felled and the scorched portion burned with 

 additional oil. 



When lodgepole pine bark has been adequately burned to kill 

 the beetles underneath, the bark flakes will curl and show white 

 on the edges. Frequently when this method is used, the spotting 

 and treating are performed at the same time. A pack train carry- 

 ing the pressure sprayers, oil, and felling tools follows the spotting 

 crew, and infested trees are treated wherever they are found. 

 This method is an economical one, and costs have averaged 

 between 68 cents and $1:05 per tree. This method cannot be used 

 on windy or stormy days, and during dry or windy weather great 



