UNITED STATES DEPARTMENT OF AGRICULTURE 



m BULLETIN No. 1112 ^M 



Washington, D. C. T December 21, 1922 



THE WESTERN YELLOW PINE MISTLETOE: 



Effect on Growth and Suggestions for Control. 



By Clarence F. Korstian, Forest Examiner, Appalachian Forest Experiment Station, 

 Forest Service, and W. H. Long, Forest Pathologist, Office of Investigations in 

 Forest Pathology, Bureau of Plant Industry. 



CONTENTS. 



Introduction 1 



Physical and climatic features of the region 2 



The western yellow pine mistletoe 3 



EfEect of mistletoe on growth of host 4 



EfEect on longevity of host 22 



Effect of mistletoe on merchantibiUty of timber 25 



Effect of mistletoe on seed production of host 25 



SiMcultural aspect of mistletoe infection 29 



Control of mistletoe 30 



Summary 34 



INTRODUCTION. 



Western yellow pine {Pinus ponderosa Laws.) occurs naturally 

 from southern British Columbia to northern Mexico and from the 

 Pacific coast to east of the one hundredth meridian. It is found in 

 the forests of every State west of the Great Plains and in many of 

 them it is one of the most important and valuable forest trees. In 

 the Southwest, western yellow pine is by far the most important 

 timber tree, constituting over 80 per cent of the commercial forests of 

 Arizona and New Mexico, approximately 30 billion board feet. 



During the past 12 years studies have been in progress to deter- 

 mine the effect of the mistletoe (RazoumofsJcya cryptopoda (Engehn.) 

 Gov.) on the grov/th and seed production of western yellow pine. 

 This parasite is the most widely distributed and one of the most 



Note. — The author's names are in alphabetical order. The writers axe indebted to Silvlculturist G. A. 

 Pearson, of the Fort Valley Experiment Station, for the permanent sample-plot data contained in Tables 

 11 and 17, for the data on the 1915 seed collection contained in Table 18, and for his general interest in the 

 investigation. 



3600°— 22— Bull. 1112 1 



