INCENSE CEDAK. 29 



ENEMIES. 



DISEASE. 1 



Incense cedar is subject to few diseases, but three of these are 

 very common. They are caused by a mistletoe (Phoradendron juni- 

 perinwn lihocedri), a rust fungus (Gymnosporangium tlasdalea- 

 nvm), and the dry-rot fungus {Polyporus amarus). The only seri- 

 ous damage to merchantable trees, however, is due to the latter. 



Polyporus o/marus attacks the heartwood of mature living trees 

 only, trees below the age of 140 years being more or less im- 

 mune. Thrifty growing trees in damp, rich soils seem to be less 

 affected than slow-growing ones on dry, poor sites; and trees with 

 large wounds are far more likely to be pecky than intact ones. 



The large annual fruiting bodies (sporophores or conchs) of Poly- 

 porous amarus invariably grow out of branch holes or pin knots, never 

 through the bark. The mature conch has the shape of a bell cut 

 lengthwise in halves. The upper side is light tan in color, the under 

 side a brilliant yellow, turning brown with age. Spores are formed 

 in enormous numbers and are carried by air currents to other trees. 

 They germinates only when they land on a wound or opening lead- 

 ing to the heartwood. Thus fire scars and branch stubs very often 

 offer them an easy entrance. The fungus attacks the heartwood, 

 honeycombing it with cavities from one-quarter inch to an inch in 

 diameter by from an inch to several feet in length. These cavities 

 are filled with a dry, brown, charcoal-like substance which char- 

 acterizes this defect and gives it its name of " dry " or " brown " rot. 

 The wood between the cavities is usually sound. 



It is often impossible to detect the presence of dry-rot from the 

 outward appearance of the tree, but there are certain infallible signs 

 by which we can tell that the timber is infected. The presence of 

 a fruiting body of Polyporus amarus, of course, indicates beyond a 

 doubt that the fungus is at work in the heartwood. But the fleshy 

 annual fruiting bodies are devoured eagerly by squirrels and the 

 larvae of a small moth that afterwards burrows through into the 

 dead bark. Later, woodpeckers chop out these larvae, so that, finally, 

 a cup-shapecl depression, pierced with numerous larvae holes, is 

 formed in the bark where the fruiting body once was. These de- 

 pressions are a certain sign of decay, and their number and appear- 

 ance indicate the extent of the dry-rot in the interior of the tree. In 

 general, the decay is more pronounced in the lower part of the tree, 

 since the fungus very commonly starts from fire scars. 



Since the entrance of the dry-rot fungus into the heartwood can 

 in a great number of cases be traced to fire scars, fire prevention and 



1 Prepared by Dr. E. P. Meinecke, pathologist, Bureau of Plant Industry. 



