JOIMAlOFAGRiaiTiAllSEARCH 



Vol. XV Washington, D. C, Dece;mber9, 1918 No. 10 



SEEDLING DISEASES OF CONIFERS 



By Carl Hartley, Pathologist, T. C. Merrill, Assistant Forest Pathologist, and ''•-• 'V ^^^ 

 Arthur S. Rhoads, Assistant in Forest Pathology, Investigations in Forest Pathology, '^'^^A/^./r; * • 

 Bureati of Plant Industry, United States Department of Agriculture ^ ^■*i<lj iA/ 



INTRODUCTION 



Because of the high cost of seed and the slow growth and delicate 

 character of seedlings during the first few weeks after germination losses 

 caused by the disease known as damping-off have been an important 

 factor in the propagation of conifers. The fact that a number of damping- 

 off parasites are able to cause practically identical symptoms, and the 

 further fact that certain physical factors sometimes cause injury resem- 

 bling damping-off, has made a study desirable, both of damping-off and 

 of the other diseases which may attack seedlings of the same age. The 

 present paper will consider all the diseases which the writers have founcj 

 attacking seedlings up to the age of approximately two months. 



DAMPING-OFF 



Damping-off is the most serious of the diseases attacking coniferous 

 nursery stock in most regions. There is considerable literature on the 

 disease both in connection with conifers and with truck crops. The 

 most important work in relation to conifers is summarized by Spaulding 

 {26)? Both etiology and control are, nevertheless, seriously in need of 

 further investigation, because of the complications arising from the 

 multiplicity of hosts and parasites involved and from the soil-inhabiting 

 tendency of several of the parasites. A summary of the available data 

 on control has been recently published (16). 



TYPES OF DAMPING-OFF IN NURSERIES 



The old conception of damping-off seems to have been the death of 

 seedlings as the result of the attack of a parasitic fungus at the soil 

 surface, causing a local constriction of the stem at that point, followed 

 by the fall and wilting of the seedling. It appears that several parasites 



1 The writers wish to acknowledge the assistance of Mr. R. G. Pierce, Mr. Glenn G. Hahn, 

 Mr. S. C. Bruner, Mr. Percy W. Scay, Mr. and Mrs. H. E. Watkins, Mrs. J. G. LiU, and Mrs. S. F. Acree, 

 in connection with parts of the isolation and inoculation work here reported. 



2 Reference is made by number (italic) to "Literature cited," pp. ss&-ss8. 



Journal of Agricultural Research, Vol. XV, No. lo 



Washington, D. C. Dec. 9, 1918 



qo (521) KeyNo. G-166 



