192 



MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTUKE 



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 9-. — Peeling Avesterii 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. 



