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



tures are above 60° F. They are most useful in the treatment of 

 broods in thin-bark trees such as lodgepole and western white 

 pine, and are usually ineffective in such thick bark trees as Jeffrey 

 pine and sugar pine. 



These penetrating-oil sprays will give 90 to 100 percent kill of 

 brood when thoroughly applied to trees with thin bark and ab- 

 sorbent bark texture, but it is often difficult to get thorough 

 coverage and uniform penetration (because of individual tree 

 bark characteristics), even when applied by careful and fully 

 experienced workmen. The use of penetrating-oil sprays has be- 

 come standard practice for controlling mountain pine beetle 

 broods in lodgepole pine in parts of the Rocky Mountain region, 

 and this method has also been used with good results in the control 

 of the Black Hills beetle in small ponderosa pines in South Dakota, 

 and for controlling the Engelmann spruce beetle in Colorado. 



Tree Injection 



Injecting chemicals into the sapstream of trees in order to 

 kill infesting insects has intrigued experimenters for more 

 than 100 years. Recently it has been tried in the control 

 of various bark beetles, particularly the mountain pine beetle in 

 western white pine stands (12), with good results under certain 

 conditions. Recently killed trees are girdled at the base by a 

 saw-kerf which penetrates through the sapwood. Then a rub- 

 berish cloth collar is attached and a solution of powdered copper 

 sulfate introduced in the collar. This is taken up by the tree and 

 the poison distributed through the trunk causing mortality to 

 bark beetles in the inner bark. The method has limitations in that 

 it must be applied within 90 days from the first bark-beetle attack 

 while the tree is still functioning; distribution of the chemical 

 is affected by blue-stain fungus, density of wood, and other 

 factors; and the difficulty of applying collars limits the method 

 to rather small-scale projects where the labor factor is not too 

 important. 



Introduction of wood-preservative chemicals into the sapstream 

 of living trees is a highly effective method of rendering wood, 

 particularly rustic work, fence posts, and small poles, resistant 

 to insect and fungus attack. Many different wood-preservative 

 chemicals can be used, but the most satisfactory are chromated 

 zinc chloride, zinc chloride, and copper sulfate, used at concentra- 

 tions of y 2 to % pound per cubic foot of sapwood to be treated. 



Logging 



Where the infestations are in accessible tracts of valuable 

 timber, the cutting and salvage of the infested trees through 

 logging operations is an effective and economical method of con- 

 trol. This method was first advocated by Hopkins — for the control 

 of Dendroctonns beetles. He proposed that the infested logs be 

 removed from 20 to 50 miles from the forest so that the beetles 

 emerging from them would find no trees to attack. Often this 

 method has been followed unwittingly by logging operators who 



