DAMPING-OFF OF CONIFEROUS SEEDLINGS. 3 



RELATION BETWEEN NURSERY METHODS AND THE CONTROL OF 



DAMPING-OFF. 



A great deal has been written, largely in horticultural journals, on 

 the methods best calculated to prevent damping-off. It has been 

 generally agreed that beds should be well drained and aerated and 

 should have no more water or shade than absolutely necessary. Sur- 

 facing beds with gravel, coarse sand, or heated sand has also been 

 recommended. All of these measures have value, but all have their 

 limitations. All of them combined are not sufficient to prevent 

 heavy losses when the damping-off parasites are present in sufficient 

 quantity. 



THE BEST SOIL FOR SEED BEDS. 



In general, where there is a chance to choose between different seed- 

 bed sites it is safest from the standpoint of damping-off control to 

 select a site with a sandy soil. Either because such soils are better 

 drained or because they contain less organic food matter for fungi, 

 damping-off is commonly less troublesome on light than on heavy 

 soils. A sandy soil is by no means a guaranty of freedom from 

 disease, the heaviest damping-off losses in the writers' experience 

 having occurred on a soil consisting of nearly pure sand. Alkaline 

 soils are believed to favor damping-off.. If this is found to be the case, 

 it may explain the fact that some of the heaviest losses from damping- 

 off occur in Nebraska and Kansas rather than in the more humid 

 Eastern States. 



Where it is necessary to put seed beds on a soil where damping-off 

 is troublesome, the soil may be improved in various ways. Where 

 sand is easily available, it may pay to haul it in and mix it with the 

 surface soil. Excellent results have been obtained in one case in the 

 writers' experience by making the entire upper 3 inches of the bed 

 of very sandy subsoil just dug up. A less expensive procedure which 

 has also given indication of value is to cover the seed with subsoil 

 taken from a point so far below the surface that it is likely to be free 

 from parasitic fungi and an unfavorable medium for their growth. 

 It is usually better to cover seed with sand than with heavy soil, and 

 surfacing the beds with coarse sand or gravel after the seed is sown 

 and covered is considered helpful. Surfacing the beds after germi- 

 nation with heated sand applied as hot as the hand can stand has also 

 been recommended. Tests by the writers of hot sand on seed beds 

 in a sandy western soil had no perceptible effect on the disease. 



AVOIDANCE OF EXCESSIVE MOISTURE. 



To secure drainage, seed beds are commonly raised from 2 to 3 

 inches above the paths, and at some nurseries the surface of the bed 

 is arched to increase run-off. This is probably good practice at most 

 nurseries, but on very sandy soils in a dry climate it does not appear to 



