The Rhizoctonia Damping-Off of Conifers 



33 



For each plat the total loss from bird injury was subtracted from the total 

 emergence. Losses from damping-off were then based upon this remainder, 

 which represented the total number of seedlings surviving bird injury and 

 from which the percentage of damping-off was calculated. It was then 

 assumed that the seedlings which were destroyed by birds would have 

 damped-off at the same rate as those which were not destroyed. The 

 final stand as indicated in the various tables therefore represents the total 

 emergence minus the sum of the actual damping-off and the theoretical 

 damping-off estimated for the seedlings removed by bird injury. The 

 data on final stand are given on the basis of nine rows in each plat. 



Essentially the same method was employed in interpreting the data from 

 the Ithaca experiment of 1925, there having been a rather uneven occur- 

 rence of losses due to mechanical breakage. 



The figures for each set of replicate plats were averaged and the probable 

 error of this mean was determined by the use of Bessel s formula. The 

 same was done for the check plats of each experiment. In view of the 

 rather limited number of replications employed, differences between any 

 two means are not considered significant unless they have at least four 

 times the value of the probable error of this difference. 



Results of the soil-treatment experiments 



The results obtained from the soil treatments are presented according to 

 the species of conifer sown in the experimental plats. 



Red pine — Liquid treatments. Preliminary field tests with sulfuric 

 acid and several mercury disinfectants were made on beds of red pine at the 

 Ithaca nursery in 1925. The beds were artificially infested with a damping- 

 off fungus (Rhizoctonia) and were maintained under rather wet conditions. 

 The incidence of disease was very high (table 8). Thus in the untreated 



TABLE 8. 



Liquid Treatments on Beds of Red Pine Sown at the Ithaca Nursery 

 on May 15, 1925 



Material employed 



Num- 

 ber of 

 applica- 

 tions 



Amount per 

 square foot 



Results (average of three replications) 



Percentage of 

 emergence 



Percentage of 

 damping-off 



after 

 emergence 



Final standtt 



Bayer compound . . 



Germisan 



Mercuric chloride. . 



Sulfuric acid 



Uspulun 



Uspulun 



rjspuiuD 



Check (untreated). 



2.58 gms.* 



1.33 gms.t 

 1.03 gms.J 



5 cc.§ 



3.01 gms. I| 



3.34 gms.f 



4.02 gms.** 



30.0±2.1 



'4o!6±i!6' 

 36.0±3.3 

 39. 7 ±1.8 

 28.7±1.4 

 35. 3 ±5. 9 

 25. 7 ±3. 9 



43. 3± 4.8 



22. 0± 3 

 61.7±10 



24. 3± 3 

 28. 0± 2 

 19. 7 ± 3 



98. 0± 0.8 



260 ±29. 9 



'536±oi'2' 

 230 ±67 . 3 

 449 ±33.0 

 307±17.1 

 442 ±85 . 7 

 8± 3.1 



* 0.7 gram in 400 cc. water at time of seeding; 0.47 gram in 270 cc. four, six, eight, and ten weeks later, 

 t 0.8 gram in 400 cc. water at time of seeding; 0.53 gram in 270 cc. four weeks later. 



t 0.33 gram in 400 cc. water at time of seeding; 0.22 gram in 270 cc. four weeks later; 0.16 gram in 270 

 cc. six, eight, and ten weeks after seeding. 



§ Kquivalent to from 5/32 to 6/32 fluid ounce of concentrated acid dissolved in 750 cc. water and 

 applied at time of seeding. 



2.34 grams in 940 cc. water at time of seeding; 0.67 gram in 270 cc. four weeks later. 



* 2.0 grams in 800 cc. water at time of seeding; 0.67 gram in 270 cc. four and six weeks later. 



** 0.67 gram in 270 cc. water at time of seeding, and repeated two, four, six, eight, and ten weeks later. 

 tt A total of 1500 seeds were sown in the area of each section from which data were obtained. 



