240 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



cases, where all the infestation is within 20 feet of the ground, 

 the barking has been done with long-handled barking spuds with- 

 out felling the trees. In such cases, of course, the work can be 

 done more cheaply than where felling the trees becomes necessary. 



Peeling and Spreading Bark 



A modification of the peeling method, in which the bark is 

 spread where it will receive the direct rays of the sun, has been 

 used with fair success in the control of the western pine beetle. 

 It is applicable to the treatment of ponderosa pines infested with 

 broods of this species late in the spring or in the summer in places 

 where burning would be dangerous. 



In this method the tree is felled across a log so as to keep a 

 large part of the trunk off the ground, and the bark is peeled 

 and spread 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, 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 so that the sun's rays may 

 strike it at an angle of not less than 45°. 



It can be readily seen that the method is tedious and expensive 

 and of limited application. Effective temperatures do not always 

 prevail during the control season, especially at high altitudes and 

 on northern exposures. The method also requires a greater atten- 

 tion to detail than can ordinarily be expected from the average 

 workman. 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 (132) is particularly 

 applicable 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 pines, especially those growing in 

 open stands and in areas where the fell-deck-burn 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. They are completely limbed and the brush cleared away 

 so that the logs will receive direct sunlight. After a few day's 

 exposure with air temperatures of 80° F. or more all the bark 

 beetles on the top half of the logs will have been killed. Then the 

 men return and with peavies turn the logs completely over so 

 that the other side will be exposed. 



This method has been very effectively used for several years in 

 control of the mountain pine beetle in Crater Lake National Park. 

 It has the advantage of being much cheaper than either the 

 peeling or burning methods; and in crowded stands it avoids 

 scorching adjacent trees, and thus does not set up influences 



