192 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 
out in the open where it will receive the direct rays of the sun. 
To be effective it is necessary to have summer air temperatures of 
85° F’. or more in order to produce fatal temperatures of 115° to 120° 
in the bark. The bark must be very carefully spread and must not 
be left in the shade of other slabs or trees. On north slopes or in. 
canyons it must be carried out to an opening or propped against 
rocks or trees in order that the sun’s rays may strike it at an “angle 
of not less than 45°. 
FIGURE 92.—Peeling western white pines infested by bark beetles by means of spuds. 
It can be readily seen that the method is tedious and expensive and 
of limited application. Effective temperatures do not always pre- 
vail during the control season, especially at high altitudes and on 
northern exposures. The method also requires a greater attention 
to detail than can ordinarily be expected from the average work- 
man. Summer control work in which this method is used has not 
proved very effective, and the method has lost favor in recent years. 
The solar-heat method 
The solar heat or sun-curing method (69) is particularly appli- 
cable to the control of bark beetles, other than the engraver beetles 
or flatheaded borers, that attack thin-barked trees of small diameter, 
such as lodgepole pine, especially those growing in open stands and 
and in areas where the deck- burning method is objectionable. 
In this method, trees are felled in a north-and-south direction 
parallel to one another and never crisscross as in the peeling method. 
