Dec. 9.1918 Seedling Diseases of Conifers 523 



attributed not at all to poor seed, but rather to abundant early infection 

 of beds with species of Pythium or Corticium, causing both the appar- 

 ently poor germination and the high damping-off loss. 



LATE DAMPING-OFF 



The term "late damping-off" is used for the damping-off as a result of 

 root infections of seedlings several weeks old whose stems have developed 

 strong supporting tissues. 



The parasites which cause normal damping-off are also probably 

 responsible for most cases of this type. Like germination loss, it differs 

 from the normal type only by the age of the seedlings concerned. How- 

 ever, the symptoms of late damping-off are very different from those of 

 the normal type; the seedlings remain erect, dry up and turn brown, 

 and in some cases even shed their leaves before the stem finally falls over 

 (PI. B, fig. 6), This type is very likely to be confused with drouth 

 injury. 



The death of seedlings due to root killing by damping-off parasites in 

 rare cases continues throughout the season, and probably even into the 

 second year in cases where development of the host species has been 

 especially slow. This appeared to be the case with Engelmaim spruce 

 (Picea engelmanni) at a mountain nursery in New Mexico. All such 

 death, up to the rather arbitrary age of two months, is classed by the 

 writers as damping-off, while similar death of still older stock is classed 

 as rootrot. This time limit is justified only by convenience. The 

 damping-off parasites do practically all of their damage at most nur- 

 series before the seedlings are 2 months old. Their work up to that 

 time is fairly easy to detect and distinguish from disease due to other 

 causes, because of the localization of most of the affected plants on the 

 margins of the old damping-off patches of normal type. Furthermore, 

 the soil treatments which control the normal type of damping-off are also 

 useful, at some places at least, in lessening damage from the late type 

 of disease. It is therefore easiest to consider all the trouble during the 

 first two months as damping-off, without tr3nng to mark any of the 

 interm.ediate stages as distinct diseases. 



The death of stock over 2 months old, on the other hand, will require 

 both different investigative methods and, very likely, different types of 

 control measures. Although sometimes caused by damping-off organ- 

 isms, there seems to be no practical advantage in considering it at the 

 same time as damping-off. 



The impression prevalent in some places that damping-off organisms 

 always infect at the soil surface is shown to be especially incorrect in the 

 case of this late type of damping-off. In one case the root of a young 

 seedling of western yellow pine (Pinus ponderosa), growing rapidly in 

 sandy soil at the outer margin of a damping-off patch, was found to 

 have been attacked at a point 1 1 inches below the soil surface. Not all 



