BLIGHTS OF CONIFEROUS NURSERY STOCK. 17 



ROOT-ROTS. 



Many soil-inhabiting fungi grow on dead roots of both seedlings 

 and transplants. There undoubtedly are soil fungi which can kill 

 living roots when conditions are favorable. A species of Fusarium i 

 is said to have caused loss by killing pine roots in a Vermont nursery. 

 Mycelial growth on roots, such as is there described, has been fre- 

 quently observed by the writer, though in only part of the cases was 

 it associated with any apparent injury to the plants. 



Rhizoctonia sp. (probably Corticiunb vagum B. and C), which 

 causes damping-off of very young seedlings, sometimes continues to 

 work in patches till the seedlings are 2 months old or even more. 

 On sandy soil, when seedlings from 5 to 9 weeks old are killed, the 

 youngest and deepest parts of the roots are usually first attacked. 

 At Halsey roots of Rocky Mountain yellow-pine seedlings about 7 

 weeks old have been attacked at points as much as 11 inches below 

 the ground surface. In many seedlings as old as this the older parts 

 of the roots resist the entrance of the fungus which has rotted the 

 younger parts and throw out new root branches, so that recovery 

 takes place without any evidence of the damage being shown by the 

 plant above ground. While we ordinarily consider damping-off as 

 the death of very young, succulent seedlings, the killing of seedlings 

 from 5 weeks to 2 months old by Rhizoctonia is merely a continuation 

 of the earlier and more typical damping-off and to a certain extent is 

 influenced by the treatments which control the early damping-off. 

 For practical purposes, therefore, only the relatively small number 

 of cases of root-rot which occur after the plants are 2 months old 

 are considered as blight; root-rot of stock less than 2 months old is 

 classed as damping-off. 



Root-rot of stock more than 2 months old does not appear to have 

 become a serious source of loss in this country. Until more is 

 learned concerning it nothing of value can be said as to characteristic 

 symptoms or control measures. 



UNCLASSIFIED DISEASES. 



STEM GIRDLE. 



In Wisconsin, Oregon, Colorado, and New Mexico the stems of 2 

 and 3 year old conifers in jiurseries have been found constricted or 

 girdled in a peculiar manner just above the ground line, and some- 

 times abnormally large just above the point of girdling. The bark 

 at the point of constriction is dead and often loose. The trees may 

 continue in apparently good health for some time after the girdling. 



1 Gifford, C. M. The damping off of coniferous seedlings. Vermont Agricultural Ex- 

 periment Station, Bulletin 157, p. 149-151, 1911. 



