FOREST AND RANGE RESOURCES OF UTAH 77 



beetles in whatever stage they may be. There is no chance of saving 

 a tree which is heavily infested with bark beetles, because if left 

 untreated the tree will be girdled and killed by the beetles themselves. 



There are also certain butterflies which in their worm or larvae 

 stage feed upon the buds and tips of the twigs of trees. The spruce- 

 bud worm is one of this family. It attacks and kills the buds and 

 ends of the limbs of Engelmann spruce, Douglas fir, and white fir 

 or balsam. 



The pine butterfly acts in the same manner except that it feeds on 

 the needles of the pine trees instead of attacking the buds and ends 

 of the twigs. 



FUNGOUS DISEASES AND PARASITES 



Although very unfavorable environmental conditions such as 

 extreme drouth, untimely frosts, and chemical fumes can cause 

 diseased conditions, most tree diseases are due to fungi and 

 mistletoes. The fungi are minute plants, consisting mainly of 

 threads visible only under the microscope. ■ Some attack the living 

 tissue of roots, leaves, or inner bark, and the most conspicuous in- 

 vade the dead heartwood of the trunk and cause its decay. En- 

 trance to woody tissues is usually at wounds. Trunk decay lowers 

 or destroys the commercial value of the tree, and trunk or root rots 

 may so weaken the tree that it is broken off or uprooted by wind. 

 The diseases of aspen in Utah have received special attention in a 

 recent bulletin (5). 



In the coniferous forests of the drier parts of the West a great 

 deal of damage is caused by the leafless mistletoes, parasitic flower- 

 ing plants even more degenerate and less conspicuous but much 

 more harmful than the leafy mistletoes of broad-leaved trees. The 

 mistletoe plants grow from a small sticky seed which attaches itself 

 to the bark of the tree and after germinating extends its roots 

 through the bark and into the cambium layer. The nourishment for 

 the mistletoe is obtained almost entirely from the food which is 

 produced for the tree ; the stems and flowers of the mistletoe plant 

 grow in the air outside of the bole or limb of the tree and are often 

 mistaken for part of the tree itself. The part of the mistletoe which 

 grows in the air is of a yellowish or greenish color and particularly 

 in the case of the Douglas fir is very small and likely to pass un- 

 noticed. The effect of the mistletoe on the tree is often to cause 

 an enlargement of the limb or bole at the point where the mistletoe 

 is attached and later to stimulate a very heavy growth of branches 

 or twigs which is commonly called a witches' broom. When only 

 a few limbs of a tree are attacked, it is often possible to save the 

 tree by cutting off these limbs at a point considerably below the 

 apparent limit of the mistletoe infection. Heavily infected trees 

 are dwarfed and deformed, and may be killed or so weakened as 

 to be readily killed by insects. The mistletoe itself dies with the 

 tree. In the meantime, it has produced seeds which spread to other 

 trees. 



The prevalence of both heart rot and mistletoe in the forest may 

 be lessened when the mature timber is harvested, by including among 

 the trees that are cut all of those in which age, wounds, or visible 

 disease signs show that they are infected or likely to become infected 



