12 



BULLETIN 034, U. S. DEPARTMENT OF AGRICULTURE. 



Table I. — Relative importance of losses by damping-off before and after conifer 

 seedlings emerge from the soil. 



Nursery and species. 



Basis. 



Bessey (Nebraska sand hi]]?): 



Pinus banksiana 



^yjgiPinus ponderosa 



1 1 1'in us resinosa 



tJS&en City (southwestern 

 Kansas): 

 Pinus austriaca 



Pinus banksiana. 

 Pinus ponderosa. 



Cass Lake (northern Minne- 

 sota): 



Pinus resinosa. 



Series. 



Average of 9. 

 Average of 2. 

 Average of 3. 



Average of 2. . 



do 



Average of 7... 



Kast Tawas (Michigan): 

 Pinus resinosa 



Fort Bayard (New Mexico): 

 Pinus ponderosa 



No. 1051 



No. 1052 



No. 1053 



No. T054 



Nos. 1057 and 

 1061. 



(1073. 

 \1074. 



Disinfectant. 



Number of 

 plats. 



Sulphuric acid 



do 



...do 



Nos. 791 and 



792. 

 Nos. 891 and 



892. 



Copper sul- 

 phate. 



Zinc chlorid. . . 



Copper sul- 

 phate. 



Formaldehyde 



do 



Zinc chlorid. . . 



do 



Heat 



Formaldehyde 

 Sulphuric acid 



Formaldehyde 7 



Sulphuric acid 8 



Treat- 

 ed. 



Con- 

 trols. 



(«) 



C) 



Loss in control plats. 





Emerged 



(viable seeds). 



Be- 

 fore. 



After. 



P.ct. 

 37.8 

 28.1 

 29.4 



80.7 

 15.3 



3.8 

 25.7 

 5.7 

 7.4 

 4.9 



58.2 

 12.6 

 14.5 



Total. 



P.ct. 

 C27.2 

 27.3 

 54. 1 



12.0 

 30.9 



37.2 

 36.2 

 26.2 

 43.6 

 16.9 



45.3 

 18.0 



Ratio 



of 

 col. 6 



to 

 col. 7. 



P.ct 



65.6 ci.39 

 55. 4 1 1. 03 

 83. 5 I . 54 



16.5 2.52 



92.7 

 46.2 



41.0 

 61.9 

 31.9 

 5.1 

 21.8 



51.2 

 76.2 



36. 1 48. 7 



6.72 

 .49 



.10 



.71 

 .22 

 .18 

 .29 



.13 

 3.25 



.35 



.78 



a Area counted, 122 square feet. & Area counted, 78 square feet. 



c In Pinus banksiana ai the Bessey Nursery, the loss after emergence is slightly low and the ratio slightly 

 high, because of the closing of counts on a few of the series before damping-off was entirely over. 



The procedure was to average the number of seedlings which 

 emerged in the control plats in each series and subtract this number 

 from the average number emerging (that is, appearing above the 

 soil surface) in the treated plats in the same series. The treated 

 plats chosen were the ones which allowed the averaging of the 

 greatest number of plats treated with the same disinfectant. Only 

 those plats were taken in which there was no evidence of injury to 

 the seed or seedlings by the disinfectant and in which the amount 

 of normal damping-off during the first few days after emergence 

 was so slight as to indicate satisfactory initial control of the parasites 

 by the treatment. In such plats it was assumed that the germination 

 loss was unimportant, and the average number of seedlings appear- 

 ing on them was taken as representing the number of viable seeds per 

 plat. The difference between this emergence figure and the average 

 emergence in the controls was taken as indicating the extent of para- 

 sitic loss before the seedlings appeared, including any destruction 

 of dormant seed by parasites which may have occurred as well as 

 the killing of germinating seed. Both this figure and the number 



