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



and the plats with the thinner stands must have been very slight, this 

 latter explanation has not much to support it. The data are believed 

 to constitute further evidence of the importance of parasites in de- 

 creasing the percentage of emergence in coniferous seed beds. That 

 the effect of parasites on emergence should have been large enough 

 in this case to make itself apparent on the face of the figures, despite 

 the variations due to other sources, is especially interesting in view 

 of the fact that the losses after emergence in these plats were not 

 high. 



ECONOMIC IMPORTANCE OF DAMPING-OFF. 



The importance of damping-off in coniferous nurseries in Europe 

 is indicated by frequent reference to- the disease in the literature. 

 Biittner (25, 26) states that whole beds are frequently destroyed by 

 it. Baudisch (9) speaks of the death of entire stands in many 

 nurseries as the result of damping-off. In the United States Spauld- 

 ing (137) considers damping-off a serious obstacle in forestation 

 operations. Clinton (28, p. 348-349) reports serious damage to 

 conifers in New England nurseries. The writer has found the dis- 

 ease especially prevalent in nurseries in Nebraska and Kansas, a some- 

 what unexpected situation in view of the relatively dry conditions 

 prevailing there. A correspondent has reported heavy loss in seed 

 beds in Texas. 



The economic importance of the disease in conifers is due in part 

 to the rather heavy average losses experienced at many nurseries 

 and in part to the irregular character of the losses. In one season 

 losses may be negligible, while the next season the beds of certain 

 species may be practically wiped out. Even without this element of 

 uncertainty the losses experienced are expensive, because of the high 

 cost of coniferous seed. The seed of some species costs from $3 to 

 $5 a pound and seldom shows a germination of more than 60 per 

 cent under nursery conditions. A loss of half of this 60 per cent from 

 parasites, both before and after the seedlings break through the soil, 

 is therefore a matter which deserves attention. The figures in 

 column 8 of Table I, obtained by adding together those in columns 

 6 and 7, show that the loss is frequently higher than this. At 

 the nurseries at which control experiments have been conducted, the 

 percentage of the seedlings in untreated beds which have been found 

 by actual count damped-off after emergence is frequently more than 

 50 per cent, in addition to the considerable but less accurately de- 

 terminable loss indicated by the foregoing data as being caused by 

 the parasites before the seedlings appear. 



It has been suggested by foresters and others that the net economic 

 damage from damping-off is not as great as is indicated by the loss 

 of seed and seedlings which it may cause. The argument is ad- 



