July o, 1917 



A Needle Blight of Douglas Fir 



lOI 



for several seasons are almost entirely defoliated and either die or merely 

 exist for an indefinite period without making any perceptible growth (PI. 

 12, B). 



Fig. 2. — Cross section through the middle of two apothecia of the needle-blight fungus, showing the 

 arrangement of the asci and spores, the diseased area of the needle, disorganized cells, and mycelium. 



The greatest damage is done in close, pure stands. Since this type of 

 stand is prevalent in many parts of Montana, Idaho, and Washington, 

 the fungus becomes a serious menace to the forest. Repeated observa- 

 tions show that when the fungus becomes once established in dense, even- 



a g e d reproduction, 

 none of the ordinary 

 conditions of climate 

 which have been 

 known to arrest other 

 needle diseases seem 

 to prevail against it. 

 It is significant, how- 

 ever, that those trees 

 of the older age classes 

 which are in a close 

 stand and which have 

 escaped the general 

 canopy are, in most 

 cases, free from the 

 disease. Douglas fir in 

 mixed stands is not so 

 frequently attacked. 

 The parasitic nature of the fungus is shown by its ability to attack the 

 young needles of the most vigorously growing trees ; also by the fact that 

 it does not attack any more rapidly the needles of trees suppressed by 

 mistletoe, root fungi, or insects. 



mm 



Fjg. 3. — Asci with mature spores of the needle-blight fungus on 

 Douglas fir. 



