6 BULLETIN 453, U. S. DEPARTMENT OF AGRICULTURE. 



to determine for any particular nursery whether or not damping-off 

 losses are regularly less in beds sown at a particular time. It is 

 thought that fall sowing is least likely to succeed in localities in 

 which the soil does not remain constantly frozen during the winter. 



TESTS OF SOIL DISINFECTION FOR THE CONTROL OF DAMPING-OFF. 



The entire matter of the factors controlling the work of the 

 damping-off parasites and the methods of seed-bed management 

 most likely to decrease the disease needs a great deal of further 

 examination. At present adherence to the best known nursery 

 practice will not avoid considerable annual losses at most nurseries 

 or prevent epidemic years in which the beds of certain species are 

 entire failures. The multiplicity of parasites and the different con- 

 ditions of soil and climate to be met so complicate the problem that 

 it has been found most profitable to make a direct attack on the 

 parasites by the use of disinfectants rather than wait for results by 

 the indirect means of changed nursery management. 



Experiments in seed-bed disinfection have been carried on by the 

 writers or in pursuance of their recommendations for the past seven 

 years and at a number of nurseries. At different times assistance 

 has been rendered by Mr. R. D. Rands, Dr. J. V. Hofmann, Dr. T. C. 

 Merrill, Mr. S. C. Bruner, and Mr. G. G. Halm. 



Definite and satisfactory control of the disease has been secured 

 by soil disinfection at every nursery in which extensive experiments 

 have been conducted, and preliminary tests at additional nurseries 

 indicate that while different places require somewhat different pro-, 

 cedure, damping-off everywhere can be controlled by proper disin- 

 fection of the seed beds. The economic results at all of these nurs- 

 eries are briefly described in the following pages, together with a 

 summary of the published results of other investigators. 



RESULTS OF SOIL DISINFECTION AT NURSERIES WHERE REPEATED TESTS HAVE BEEN 



MADE. 



The first tests were made in pine seed beds in the very sandy soil of 

 the United States Forest Service nursery at Halsey, Nebr. The ex- 

 perience at this nursery was in many ways typical and will therefore 

 be described in some detail. 



The first attempt was to control the disease by applying disin- 

 fectants after the seedlings appeared above ground. This failed, 

 partly because the disinfectants injured the seedlings and partly be- 

 cause the parasites were found to do a great deal of their work before 

 the seedlings came up. A number of disinfectants were then tested in 

 applications at or before seed sowing. Of these, commercial sulphuric 

 acid appeared the cheapest and most effective. Both heat and formal- 

 dehyde, the means usually recommended for disinfecting greenhouse 

 and truck soils, proved less reliable as well as more expensive. 



