MISTLETOE INJURY TO CONIFERS. 27 



GENERAL SUPPRESSION AND FUNGOUS ATTACK. 



Aside from the fact that fungous enemies enter these conifers 

 through broken branches, lesions, and burls caused by mistletoe, 

 heavily infected trees are, owing to their weakened condition, more 

 susceptible to fungous attack on any part roots, trunks, or leaves. 

 In the lake region of Idaho the larch of all ages and conditions is 

 at present suffering from an epidemic of a needle disease, Hypoder- 

 mella laricis Tub. It is observed that in practically every instance 

 the needles of very old mistletoe brooms are first attacked, whereas 

 those of the uninfected trees of particular age classes or exposures 

 may ward it off for a longer period. 1 It is a common observation 

 that in regions of heavy mistletoe infection (and no\vhere is it better 

 shown than in the forests of eastern and central Oregon and many 

 parts of Idaho and Montana) many heavily infected trees are in 

 a dead and dying condition. If these trees are carefully examined 

 with reference to average healthy growth for the region, it will be 

 found that they have died prematurely. 



It has already been indicated that mistletoe is capable of causing 

 the death of its host in some instances. The whole tendency of the 

 parasite is to reduce the life functions of its host to the lowest point, 

 and if death does not result from this cause alone the way is opened 

 to various secondary agents, which may or may not attack vigorously 

 growing trees. The gradual thinning out of the foliage of heavily 

 infected trees and the appropriation by the brooms of much of the 

 elaborated food materials must necessarily result in an unbalanced 

 relation between the crown and the root system. Consequently, there 

 may be a dearth of food materials for the latter, wholly inadequate 

 to support its present extent. It may be naturally inferred that this 

 results in the suppression of the roots or a dying off of the more 

 extended members of the system. A close examination of a hundred 

 or more windfalls of heavily infected Douglas fir, yellow pine, and 

 larch in the regions above mentioned shows quite clearly that the 

 horizontal and brace roots of these trees in most cases were badly 

 decayed. Since few windfalls of the heavily uninfected trees of 

 the same average age and size were observed in the same region, 

 it may be inferred that a possible relation existed between the sup- 

 pressing effects of the mistletoe and the decay in the roots. Armil- 

 laria mellea (Yahl.) Quel. was definitely associated with some of 

 the decay in the roots. In most cases, however, owing to the absence 

 of fruiting stages, the cause of the rot in the fallen trees could not 

 be determined. 



1 Hypodermella laricis was first named and described by Von Tubeuf on the European 

 larch (Larix curopaea} . This is the first note of its occurrence in North America. The 

 fungus, characterized by its four clavate spores to an ascus, is very destructive and is the 

 cause of considerable damage in the larch forests of the northwestern United States and 

 Canada. 



