THE PROGRESS OF FOREST PATHOLOGY 



By CARL HARTLEY, J. S. BOYCE, and others 1 in the Division of Forest Pathol- 

 ogy, Bureau of Plant Industry 



CONTENTS 



Page 



Introduction 695 



Forest deterioration by native diseases 695 



Diseases affecting nurseries 695 



Diseases affecting plantations 696 



Diseases affecting immature forests 699 



D iseases affecting merchantable forests 70 1 



Relation of forest diseases to recreational use and watershed 



protection 705 



Deterioration of killed timber 706 



Deterioration of forest products 707 



Forest deterioration by introduced diseases 710 



Present status of research and control 717 



Agencies active 717 



Control practices 719 



INTRODUCTION 



Among the diseases are included not only those caused by fungi, 

 bacteria, mistletoes, and other types of parasitic plants, but also the 

 unhealthy conditions resulting from such causes as frost, excessive 

 heat, and poisonous gases. Some of the effects of drought, wind, 

 fire, and mechanical injuries are sufficiently like those of parasites or 

 have such an influence on the course of the parasitic diseases that for 

 practical purposes they are also classed among the diseases. Insect 

 injury is considered elsewhere, though there are some cases in which 

 the insects and plant parasites work in such close partnership that 

 they cannot be entirely separated. 



Diseases affect forest productiveness in three ways by killing trees, 

 by slowing down tree growth, and by degrading or destroying the 

 wood after it is grown. Reliable loss figures are available for only a 

 single kind of damage, i.e., decay of wood that has already grown, 

 and even for decay they are available for only a few of our forest-tree 

 species. Diseases sometimes lower the value of the forest for recrea- 

 tional use by rendering it unsightly and occasionally hurt its effective- 

 ness in watershed protection. Direct control measures are being 

 applied on a considerable scale only in forest nurseries and against 

 blister rust in the white-pine forests. 



FOREST DETERIORATION BY NATIVE DISEASES 

 DISEASES AFFECTING NURSERIES 



There are a number of diseases that have caused serious loss in 

 nursery stock in the past. The obvious result has been unnecessarily 

 high cost of planting stock at the nurseries where disease has been 

 most prevalent. Even a very moderate increase in plantation cost 



i Especially S. B. Detwiler, E. P. Meinecke, W. W. Wagener, E. K. Seattle, and Lake S. GUI. 

 168342 33 vol. 1 45 695 



