8 BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 



dence of the relatively small amount of actual investigation carried 

 on there on this disease in the nurseries. A number of references to 

 the damping-off of conifers in the English horticultural and botani- 

 cal literature yield even less definite information as to the causal 

 fungi than do the German articles. 



With the awakening of interest in reforestation in the United 

 States between 15 and 20 years ago and the first efforts to grow 

 pines in quantity for forestry purposes, attempts were made to de- 

 termine the cause of the disease in this country and to develop direct- 

 control methods. Duggar and Stewart (32) made what appears to 

 be the first report of Rhizoctonia in connection with the damping-off 

 of conifers. Spaulding (136, 137), in work begun in 1905, con- 

 tributed much to our knowledge of the etiology of the damping-off 

 of pine in this country, especially in relation to Fusarium, and origi- 

 nated the sulphuric-acid method of control. The Avriter in 1910 re- 

 ported preliminary inoculations on conifers with both Khizoctonia 

 and Pythium debaryanum (02). The work of Gifford (46) and 

 Hofmann (77) added to the information on the causal relation of 

 Fusarium, spp. and P. debaryanum^ respectively. Hartley, Merrill, 

 and Rhoads (68) have recently established the parasitism of a num- 

 ber of strains of the Corticium vaguni type of Rhizoctonia on pine 

 seedlings under inoculation conditions, have confirmed Spaulding's 

 conclusions as to the parasitism of Fusarium moniliforme Sheldon, 

 and have given preliminary data on other fungi. They consider P. 

 debaryanum and C. vagum more important in pine seed beds than any 

 single Fusarium species. Hartley and Hahn (69) have announced 

 successful inoculations on pines with P. debaryanum and Rheospo- 

 rangium aphanidermatus Edson, with less satisfactory evidence of 

 the parasitism of Phytophthora sp. and a fungus tentatively referred 

 to Pythium artotrogus. Hartley and Pierce (67) report the finding 

 of P. debaryanum in Tsuga mertensiana and Pseudotsuga taxifolia 

 as well as in the pines. In damped-off pine seedlings they find P. 

 debaryanum more commonly than C. vagum, especially in beds which 

 have received disinfectant treatments. Other considerations, how- 

 ever, keep them from concluding that the former is necessarily the 

 more important of the two. Both of these latter papers and all of 

 the reports of Pythium with the exception of Hofmann's are brief 

 notes, presenting no evidence in support of the statements made. 



DESCRIPTION. 



The symptoms of damping-off in conifers have already been de- 

 scribed in some detail (68). In the paper cited, injury due to exces- 

 sive heat of the surface soil and injury caused by high wind, both of 

 which may easily be confused with damping-off, are described and 

 accompanied by colored illustrations both of different types of damp- 



