190 MISC. PUBLICATION 2738, U. 8. DEPT. OF AGRICULTURE 
the amount of space available so that neighboring living trees will 
not be injured. If this precaution is not taken, the scorched trees may 
draw in additional infestation and more or less nullify the effects of 
the control work. 
The otl-burning method 
Recent control technique has developed an economical method of 
killing bark beetles in thin-bark trees, such as lodgepole pine, by 
spraying the bark with fuel oil, firing it, and letting the bark be 
scorched deeply enough so that the beetles will be killed by the 
heat. The trees may be either felled and burned or burned in a 
standing position. 
A fuel oil is used that has a high caloric content and burns 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° Baumé 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°+ Baumé 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 one-half to three- 
fourths of a 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. 
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 trdin carrying the pressure 
sprayers, oil, and felling tools follows the spotting crew, and in- 
fested 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. While the method is effective in ordinary weather it can- 
not be used on windy or stormy days, and during dry or windy 
weather great care must be used to avoid serious conflagrations. 
This method is limited to the treatment of thin-barked trees such as 
lodgepole pine, to trees of moderate height that can be burned as 
high up as the infestation, and to situations where the fire hazard is 
not too great. 
Lodgepole pine growing in dark woods or in dense thickets of 
underbrush where the sun-curing method is not effective, or tall trees 
which cannot be successfully treated in the standing position, can 
be felled and burned with oil in places where decking and burning 
in piles would not be feasible. A slow-burning fuel oil is used, and 
the fire is carried along and confined to the bole of the tree by spray- 
ing on oil from a hand pump. Two men follow. behind the fireman 
and quickly extinguish any fire left on the tree or starting on the 
ground. It is surprising in what hazardous areas this method can 
be used without difficulty. 
