30 BULLETIN 55, U. S. DEPARTMENT OF AGEICULTUEE. 
SUSCEPTIBILITY TO DISEASE AND INJURY. 
FUNGI. 
Balsam fir must be classed as one of the most defective of our 
northeastern conifers. Its chief enemies are fungi, and the weakest 
point of attack is the heartwood. 
According to its place of origin, the rot is known as top or ground 
rot, and is caused by two different species of fungi, Trametes pini and 
Polyporus scliweinitzii. 1 The latter affects the merchantable portion 
of the tree, and therefore does the most injury. Even when the rot 
does not extend far up the trunk, the tree is nevertheless lost in 
lumbering, since the choppers, finding the butt rotten, will in many 
cases leave it partly cut through, to be broken down by the first wind. 
Thus is the whole tree wasted, although at a short distance from the 
ground it might be perfectly sound. The roots are the chief points 
of entrance for ground rot. Ground rot is especially common in 
balsam on slopes in mixture with hardwoods. Its relative infre- 
quency in the swamps is most likely due to the excess of water and 
poor aeration in the soil, as well as the antiseptic effect of bog water. 
Ground rot may also find entrance through wounds on the lateral 
roots. Being near the surface and extending for several feet from 
the base of the tree, these are readily injured in logging by falling 
trees or by logs dragged over them. Roots may also be wounded by 
sharp rocks, or they may be broken by a strong wind, or insects 
may puncture them. In many cases ground rot was found to be 
associated with deep frost cracks and holes made by ants. 
Top rot, affecting the upper and less merchantable part of the tree, 
is less common than ground rot. It was especially noted in sup- 
pressed trees, the tops of which are often injured by rubbing against 
other trees, though any kind of a wound in the top may afford an en- 
trance to the fungus. Balsam fir beneath hardwoods is often sup- 
pressed for many years, and is therefore likely to be affected by rot 
in the top. The same is true of dense, pure stands, in which sup- 
pressed trees eventually die from the top. 
Not many opportunties were afforded to study the rate at which 
the rot spreads, because it was impossible to tell when a frost crack 
or an insect wound was made. Only woimds made by falling trees, 
the axe, etc., could be used. The heartwood on the stump was, as 
a rule, completely rotten if the wound had been made low down 
upon the tree from five to seven years before. During that time the 
rot had extended upward for from 5 to 10 feet. The rate of spreading 
at the top was less rapid. 
^edgcoek, George G. Notes on Some Diseases of Trees in our National Forests, II. Phytopothol- 
ogy 2: 77-78, April, 1912. 
