6 MANUAL OF TREE DISEASES 



obtained by digging three or four feet below the surface. This 

 furnishes a surfacing for the bed which is sterile and easy to 

 keep relatively dry. 



The beds should be covered and kept moist enough to pro- 

 mote germination. After the seeds have germinated, partial 

 shade should be furnished on bright days but should be removed 

 in cloudy weather, in order to allow as much evaporation as 

 possible from the siu-face of the soil. These precautions are 

 especially important if it is warm and rainy. If the siu-face 

 of the soil does not dry sufficiently, more clean coarse sand may 

 be scattered over it. 



(2) Eradication. 



Two general eradication methods are recommended for the 

 control of damping-off: (1) disinfection of the soil before 

 planting, usually with formaldehyde; and, (2) for coniferous 

 seedlings only, disinfection at the time of planting with sulfuric 

 acid. 



If damping-off has previously occurred in a bed, the best 

 practice is to remove the top-soil and substitute new soil. This 

 is desirable since a large accumulation of the resting spores of 

 the causal pathogene is to be expected after a severe outbreak. 

 The following steps are essential for thorough disinfection: 



A solution of formalin should be made by adding one gallon 

 of formalin (which should contain forty per cent formaldehyde 

 by volume) to fifty gallons of water. 



The soil should be prepared by forking or raking. The 

 formalin solution may then be applied to the bed with a sprin- 

 kling-can, using about two quarts for every square foot of soil 

 to be treated. If the nature of the soil is such that this amount 

 cannot be put on in one application, as much as possible should 

 be applied without making the soil muddy and the remainder 

 added a few hours later. 



The bed should be covered as securely as possible with 

 heavy paper or other impervious material for forty-eight hours. 



