BULLETIN OF THE 



No. 44 



Contribution from the Bureau of Plant Industry, Wm. A. Taylor, Chief. 

 December 12, 1913. 



THE BLIGHTS OF CONIFEROUS NURSERY STOCK. 



By Carl Hartley, 

 Assistant Pathologist, Office of Investigations in Forest Pathology. 



INTRODUCTION. 



There has been a good deal of complaint from forest and orna- 

 mental nurseries in various parts of the country of injury to conifers 

 by blight. All cases in which trees in the nursery turn brown and 

 die, in whole or in part, without any very definite symptom to indi- 

 cate what caused death are classed as blight. 



The damping-off diseases and those caused by the rust fungi, de- 

 tailed descriptions of which may be found in a bulletin by Spaulding, 1 

 are not included under the name " blight." Damping-off attacks only 

 very young seedlings, doing most of its damage during the first three 

 weeks after germination. It is caused by several parasitic fungi 

 which attack the soft tissues of the tender seedlings and rot them, 

 often entirely destroying great numbers of plants in a few days. 

 Unfortunately one of these fungi sometimes continues to kill seed- 

 lings for a time after they have become older and tougher, so that 

 they look more as if they had been killed by a blight than by 

 damping-off. 



Because of the difficulty in finding a natural dividing line be- 

 tween the damping-off diseases and the blights, it has become neces- 

 sary to draw an arbitrary line between them. All parasitic death of 

 seedlings less than 2 months old will be classed as damping-off. The 

 reason for this classification will be presented under the heading 

 " Root-rots." The present paper will consider as blights only diseases 

 of stock more than 2 months old. Since the rust fungi are not com- 

 mon in our nurseries and make their presence known before the 

 death of the plant by swellings of the stems and by the breaking out > 

 of orange-colored spore pustules, there should be no difficulty in dis- 



1 Spaulding, Perley. The blister rust of white pine. U. S. Department of Agriculture,, 

 Bureau of Plant Industry, Bulletin 206, 88 p., 2 pi., 5 fig., 1911. 



13745°— Bull. 44—13 1 



