UNITED STATES DEPARTMENT OF AGRICULTURE 
1 BULLETIN No. 934 
^yjlfy Contribution from the Bureau of Plant Industry 
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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 Pathologist, Office of Investigations in Forest 
Pathology. 
CONTENTS. 
Page. 
Damping-off in general , 1 
Damping-off of conifers 7 
Causal fungi 27 
Corticium vagum , 27 
Fusarium spp 34 
Pythium debaryanum 35 
Rheosporangium aphanider- 
matus 55 
. Phytophthora spp 59 
Miscellaneous phyeomycetes 61 
Other fungi 64 
Relative importance of the damping- 
off fungi on conifers 65 
Page. 
Damping-off fungi as causes of root- 
rot and late damping-off 70 
Relation of environmental factors to 
damping-off 73 
Density of sowing 74 
Moisture and temperature factors 75 
Chemical factors 79 
Biologic factors 82 
Acknowledgments . S6 
Summary S6 
Literature cited 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 
clamped-off before they break through the soil (66). x The same term 
is even used for diseases affecting the prothallia 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 would 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. 934—21 1 
