DAMPING-OFF OF CONIFEROUS SEEDLINGS. 13 



RESULTS OF SOIL DISINFECTION IN GREENHOUSE TESTS. 



In the greenhouses of the Department of Agriculture at Washing- 

 ton, D. C, disinfection of soil by steam pressure has proved reason- 

 ably effective in controlling damping-off of pine seedlings in most of a 

 rather large number of tests conducted during the winter months. 

 During the summer there is so much reinfection that the results of 

 heat disinfection are uncertain. A single test of sulphuric acid in 

 the spring of 1915 indicated the value of acid treatment in reducing 

 damping-off in the greenhouse. Four flats of jack pine were treated 

 with sulphuric acid in quantities of three-sixteenths to three-eighths 

 ounce per square foot just after sowing. The relative survival~in the 

 acid flats, taking the average survival in the untreated flats as 100, 

 was 128. The relative survival in flats disinfected by steam was only 

 105. Three-sixteenths ounce of acid per square foot gave as good 

 results as heavier treatments. The soil used in this experiment was 

 a mixture of seven parts loam, four parts sand, two parts manure, 

 and one part leaf mold. 



RESULTS IN DISINFECTING THE SOIL OBTAINED BY OTHER INVESTIGATORS. 



Spaulding, 1 who appears to have been the originator of the use of 

 sulphuric acid for soil disinfection, has tested acid and other disin- 

 fectants at several places. In greenhouse tests formaldehyde and 

 copper sulphate were found valuable, but the sulphate injured seed- 

 lings. At Saranac Inn, N. Y., formaldehyde apparently increased 

 damping-off one season and controlled it in a later season, while 

 sulphuric acid injured seedlings and gave results which from the 

 economic standpoint were inconclusive. 



At Burlington, Vt., results with disinfectants in pine-seed beds have 

 been reported by Spaulding, 2 Jones, 3 Gifford, 4 and Burns. 5 Formal- 

 dehyde applied five days before sowing and allowed to evaporate for 

 two days before sowing killed part of the seed. All of the writers 

 found formaldehyde of decided value in controlling damping-off. 

 Jones and Spaulding report a single test in which but one-tenth 

 ounce (0.106 ounce) of formaldehyde was used per square foot and 

 excellent results obtained. The subsequent tests reported have been 

 with amounts of 0.48 ounce or over per square foot. The treatment 

 used by Burns, of 0.58 ounce of formaldehyde per square foot, applied 



1 Spaulding, Perley. The damping-off of coniferous seedlings. In Phytopathology, v. 4, no. 2, p. 73-88, 

 2 fig., pi. 6. 1914. 



The treatment of damping-off in coniferous seedlings. U. S. Dept. Agr., Bur. Plant Indus. Circ. 



4, 8 p. 1908. 



2 Spaulding, Perley, 1914. Op. cit. 



3 Jones, L. R. The damping-off of coniferous seedlings. In Vt. Agr. Exp. Sta. 20th Ann. Rpt., 1906-7, 

 p. 342-347. 1908. 



4 Gifford, C. M. The damping-off of coniferous seedlings. Vt. Agr. Exp. Sta. Bui. 157, p. 141-171, 10 fig., 

 4 pi. 1911. 



5 Burns, G. P. Studies in tolerance of New England forest trees. I. Development of white pine seedlings 

 in nursery beds. Vt. Agr. Exp. Sta. Bui. 178, p. 125-144, 2 fig., 4 pi. 1914. 



