UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 934 



Contribution from the Bureau of Plant Industry 

 WM. A. TAYLOR, Chief 



Washington, D. C. 



PROFESSIONAL PAPER 



June 16, 1921 



DAMPING-OFF IN FOREST NURSERIES. 



By CARL HARTLEY, formerly Putlutloijixt, Office of Investigations in 'Forest 



Pathology. 



CONTENTS. 



Damping-off in general 



Damping-off of conifers 



Causal fungi 



Corticium vagum 



Fusarium spp 



I'ythium debaryanum 



Rheosporaugium aphanider- 



matus 



Phytophthora spp 



Miscellaneous phycomycetes 



Other fungi 



Relative importance of the damping- 

 off fungi on conifers 



Page. 

 1 



34 

 35 



55 

 59 

 61 

 64 



65 



Damping-off fungi as causes of root- 

 rot and late damping-off 



Relation of environmental factors to 



damping-off 



Density of sowing 



Moisture and temperature factors.. 



Chemical factors : 



Biologic factors 



Acknowledgments 



Summary 



Literature cited 



Page. 

 70 



73 



74 

 75 

 79 



82 

 86 

 86 

 91 



DAMPING-OFF IN GENERAL. 



Damping-off is the commonest English name for a symptomatic 

 group of diseases affecting great numbers of plant species of widely 

 separated phylogenetic groups. It is commonly used for any disease 

 which results in the rapid decay of young succulent seedlings or soft 

 cuttings. Young shoots from underground rootstocks may also be 

 damped-off before they break through the soil (66). 1 The same term 

 is even used for diseases affecting the protha.llia of vascular crypto- 

 gams (2). The name apparently originated in the fact that the dis- 

 ease is usually most prevalent under excessively moist conditions. 

 In those cases in which the disease becomes serious without the pres- 

 ence of unusual amounts of moisture the term is a misnomer. It is, 

 however, so thoroughly established in practical use that it w^ould be 

 impossible, even if desirable, to establish any other name. 



1 The serial numbers in parentheses refer to " Literature cited," at the end of this 

 bulletin. 



19651 Bull. 93421 1 



