18 BULLETIN 1060, U. S. DEPARTMENT OF AGRICULTURE. 



CAUSES OF INJURY. 



FUNGI. 13 



Sitka spruce, in common with other forest trees, is attacked by 

 two broad groups of fungi — first, those reducing the annual incre- 

 ment ; and, second, those reducing the merchantable timber. 



In the first group there are two rust fungi. One of these is a broom- 

 forming rust (Peridermium coloradense) . The mycelium of the 

 fungus is perennial in the twigs of the host, causing pronounced 

 witches' brooms. As a rule, this fungus is not serious, but it may 

 completely dwarf and deform small trees. 



The other rust fungus (Peridermium decolorans) does not cause 

 any deformation of the host. The mycelium confines itself to the 

 infected needles and does not enter the twigs or branches. The 

 parasite is usually confined to small trees of the sapling and small- 

 pole sizes. 



Another needle disease of importance is characterized by a brown- 

 ing of the individual needles. This fungus is Lophodermium macro- 

 sporum or a closely related species. Infected needles are invariably 

 killed and drop off, but the degree of infection varies. Sometimes 

 only occasional needles are diseased; at other times most of them 

 may be killed. The disease usually attacks the lower branches of 

 young trees. It has been reported as very prevalent along the lower 

 Columbia River in Clatsop County, Oreg. 



It is impossible to give an estimate of the amount of damage 

 caused by the needle and twig diseases just mentioned. It is obvious 

 that there must be a greater or less reduction in annual increment 

 of the infected trees, but no exact data are available. Control meas- 

 ures need not be discussed, as present economic conditions preclude 

 such work, except for nursery stock or trees of high aesthetic value. 



By far the most important fungi are those which reduce the mer- 

 chantable volume by attacking and destroying the heartwood of 

 living trees. 



The most serious of these on Sitka spruce is the ring-scale fungus 

 (Trametes pint) which causes the common red rot or conk rot in the 

 heartwood of living trees. In spruce the attack may be made at any 

 point along the bole. In the split section the decayed wood has a 

 reddish color in its early stages, and later small white sunken spots 

 are found separated by apparently sound reddish wood. The fungus 

 gains entrance to the heartwood of the trees principally through old 

 branch stubs and is exceedingly destructive in mature and over- 

 mature stands. Plates XVI (fig. 2) and XVII are illustrations of 

 this fungus. 



Next in importance is the velvet-top fungus (Polyporus schwei- 

 nitsii), which causes a pronounced butt rot. The sporophores ap- 



13 Prepared in collaboration with Dr. J. S. Boyce, Pathologist, Bureau of Plant Industry. 



