UNITED STATES DEPARTMENT OF AGRICULTURE 





Contribution from the Bureau of Plant Industry 

 WM. A. TAYLOR, Chief 



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Washington, D. C, 



PROFESSIONAL PAPER 



January 20, 1917 



THE CONTROL OF DAMPING-OFF OF CONIFEROUS 



SEEDLINGS. 



By Carl Hartley, Forest Pathologist, and Roy G. Pierce, Forest Assistant, Office of 

 Investigations in Forest Pathology. 



CONTENTS. 



The disease 1 



Economic importance of daniping-ofl 1 



Relation between nursery methods and the 



control of damping-ofl 3 



Tests of soil disinfection for the control of 



damping-ofl 6 



Soil-disinfection tests summarized 14 



Page. 



Cost of disinfectant treatments 19 



Secondary advantages from disinfectant treat- 

 ments 21 



Conclusions as to soil disinfectants 24 



Soil treatments recommended 28 



Summary 31 



THE DISEASE. 



Damping-off is a term commonly used to describe the disease caus- 

 ing the death of very young seedlings due to various parasitic fungi. 

 The damping-off of conifers in the United States has been found to 

 be caused by the fungi Pythium debaryanum Hesse, Fusarium mo- 

 niliforme Sheldon, and the common American Rhizoctonia, usually 

 referred to as Corticium vagum B. and C. var. solani Burt. Other 

 species of Fusarium and other fungi are probably also concerned to 

 a less extent. Most affected seedlings promptly fall over and decay. 

 Those which are not attacked till they are 4 to 8 weeks old may have 

 such wiry stems that they merely turn brown and remain standing 

 after death. This later type of injury is caused by parasites in the 

 same way as the decay of the more succulent younger seedlings, 

 though nurserymen do not always recognize it as the same thing. 



ECONOMIC IMPORTANCE OF DAMPING-OFF. 



Damping-off has been a handicap to nearly all nurserymen who 

 raise conifers from seed. In most nurseries a large number of seed- 

 lings are lost every year. The loss is ordinarily considerably heavier 

 than the nurseryman realizes. Very young seedlings decay and dis- 

 appear so soon after infection that the number of dead seedlings 



60142°— Bull. 453—17 1 



