UNITED STATES DEPARTMENT OF AGRICULTURE 



A BULLETIN No. 317 i 



Contribution from the Bureau of Plant Industry 

 WM. A. TAYLOR, Chief 



SW<¥Lru 



Washington, D. C. 



PROFESSIONAL PAPER 



January 20, 1916 



LARCH MISTLETOE: SOME ECONOMIC CONSIDER 

 ATIONS OF ITS INJURIOUS EFFECTS. 1 



By James R. Weir, 

 Forest Pathologist, Office of Investigations in Forest Pathology. 



CONTENTS. 



Page. 



Introduction 1 



The larch mistletoe 3 



The forest 3 



Physical and climatic features of.the 



forest region 5 



Fungous enemies of the larch 11 



Page. 



The effects of mistletoe on its host 12 



Effect of mistletoe burls on the mer- 

 chantability of larch trees 22 



Method of control 23 



Conclusions 24 



INTRODUCTION. 



During the past four years, in connection with other pathological 

 problems in the forest, the writer has made an extensive survey of 

 the damage to forest growth by some of the mistletoes of coniferous 

 trees. These parasites are very Avidely distributed in the forest 

 regions of the Northwest, and occur in such abundance in many 

 localities as to assume a very serious aspect in relation to many 

 forest problems. The extent and nature of the injury done vary 

 greatly with the forest type, the topography, and, in some respects, 

 with the climate. This is well shown in the regions in which investi- 

 gations are now being conducted. In the dense part of many forest 

 regions, as in the vicinity of the great lakes of Idaho, mistletoe does 

 but little damage. However, in the more open stands bordering on 

 the lakes or along the edge of the valleys of the Priest and Pend 

 Oreille Rivers mistletoe occurs so abundantly on the various conifers 

 as to interfere seriously with the development of some of the more 

 valuable timber trees. About the shores of Lake Coeur d'Alene, 



1 The writer wishes to express his thanks to Mr. J. F. Pernot, without whose assistance 

 the analysis of the trees would have been difficult, and to Mr. E. E. Hubert for assistance 

 in the tabulations. 



8521°— Bull. 317—16 1 



