GENERAL DISEASES 



The diseases discussed t)elow are present upon so man}^ 

 different species of plants that it would seem that they are 

 almost indifferent to the nature of their hosts. They may, 

 therefore, be expected upon any kind of plant, and are here 

 mentioned so that it will not be necessary to discuss them 

 repeatedly in succeeding pages. Special reference is also 

 made to them under the hosts upon which they are most 

 destructive. 



© Damping-off. ^"' ^^' ^- — Seedlings, cuttings, and other 

 weak, soft plants which lack in the vigor that affords them 

 natural protection against their enemies, are subject to a 

 disease which has come to be generally known to gardeners as 

 "damping-off." Damping-off is most injurious to seedlings 

 grown indoors or under crowded conditions, but it some- 

 times occurs in the field. It is particularly injurious to 

 seedling trees in the nursery where many young seedlings die 

 and disappear, or even die ])efore they come above ground. 

 The loss is thus often 90 per cent of the stand. Typically 

 damping-off occurs upon seedlings as a rot originating at or 

 near the surface of the ground. The decay at this point so 

 weakens the stem that the plant topples over or "damps- 

 off." Subsequently the whole plant may decay, either 

 from the primary cause or from secondary attacks. A short 

 time prior to the fall of the plant the leaves may appear 

 sickly, although this sign is so evanescent that it may not be 

 noted. 



Upon cuttings the toppling over does not, of course, occur, 

 but the rot at the ground line is of the same nature as in 

 the case of seedlings, and since the diseases in the two cases 

 are of similar nature and due to similar causes, they are 

 placed under the same caption. 



Damping-off may be caused by any one of several species 

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