DAMPING-OFF OF CONIFEROUS SEEDLINGS. 5 



Lime in small quantities has had no appreciable effect, while applica- 

 tions at the rate of 1 ton per acre to beds of jack pine (Pinus banksi- 

 ana Lamb.) in Nebraska have had bad effects. At Burlington, Vt., 1 

 wood ashes have been added to seed beds with disastrous results. 

 Lime also caused trouble at Burlington. At Providence, R. I., 

 a mixture of coal and wood ashes tested by Prof. H. H. York 

 seemed to give bad results. Heavy applications of imperfectly rotted 

 horse manure have been known to greatly increase damping-off at 

 the Nebraska nursery, but at the same nursery well-composted 

 manure seems harmless. It is probably safest to manure beds at 

 least a year before seed is to be sown on them. No trouble has been 

 observed to result from the use of green manures, but it may be 

 found that some such crops harbor damping-off parasites and should 

 be avoided. The perennial ragweed of the Southwest {Ambrosia 

 psilostachya DC.) serves as a hold-over host for parasitic strains of 

 Corticium, so that this and any other weeds known to carry seedling 

 parasites should be eliminated from nursery areas. 



DENSITY OF SOWING. 



As with truck crops, it is found that pines suffer most from damping- 

 off when sown too closely. A bed containing a stand of seedlings 

 which is too dense will not only lose more seedlings than a less 

 crowded bed, but it will lose a higher percentage of its seedlings. 

 This is due to the ease with which the parasites spread from one 

 seedling to another in dense stands. It has also been found with 

 jack pine that in tests at two nurseries the damping-off loss in seed- 

 lings sown broadcast was only four-fifths as great as in adjacent 

 plats sown in drills. In general, beds sown broadcast seem to suffer 

 less from damping-off than beds sown in drills, though with western 

 yellow pine broadcasting has given no better results than the drill 

 method at the nurseries where comparative tests were made. 



TIME OF SOWING. 



Another item in nursery practice in which variation may affect 

 damping-off is the time at which seed is sown. At some nurseries 

 it makes little difference when seed is sown. In one season beds 

 sown in early spring suffer least from the disease. The next season 

 the latest sown beds may come out the best. However, at some 

 nurseries it is found that there is a best time and a worst time for 

 seed sowing. In a New Mexico nursery it has been demonstrated 

 that July, the local rainy season, is the worst sowing time from the 

 damping-off standpoint. At two western nurseries (in Nebraska and 

 Colorado) the Forest Service has found that yellow-pine seed beds 

 sown in late autumn are comparatively free from damping-off. 

 Repeated tests during two or three successive seasons are necessary 



i Gifford, C M. Op. cit. 



