54 PRACTICAL PLANT PROPAGATION 



germinations are frequently due to this cause rather than to inferior 



Useful facts are given by Hartley and Pierce in "Professional 

 Paper No. 453" of the United States Department of Agriculture, 

 of which bulletin the following is the summary: 



(1) By damping-off is meant the killing of very young seedlings 

 by parasitic fungi. It is the most serious difficulty encountered in 

 raising coniferous seedlings. 



(2) To decrease losses from the disease excessive moisture and 

 shade should be avoided. Caution must be used in following this 

 recommendation or many seedlings may be killed by drought or 

 by white-spot injury to the base of the stem. Damping-off can 

 often be decreased by putting beds on very sandy soil. Seed should 

 not be sown any thicker than necessary. It appears better to sow 

 broadcast than in drills. Late Fall sowing results in decreased 

 losses at some nurseries and is worth trial. Proper attention to all 

 of these measures will decrease the losses from damping-off, but at 

 most nurseries they are not sufficient really to control the disease. 



(3) The addition of lime, wood ashes, and in some cases nitrog- 

 enous fertilizers seems to increase damping-off. Soil alkalinity 

 appears to favor the disease. No effect has been noted from green 

 manures. The use of unrotted stable manure has had very bad 

 results; properly rotted manures seem less objectionable. Tankage, 

 charcoal, and cane sugar are the only non-disinfectant substances 

 which have to date given any hope of disease control. 



(4) Soil disinfection has so far proved the best method of com- 

 bating damping-off. Of many methods tested, treatments with 

 sulphuric acid, copper sulphate, zinc chlorid, and formaldehyde 

 have proved the most satisfactory. The disinfectants, however, 

 behave quite differently at different nurseries. The acid has on 

 the whole given the best results. Heat disinfection has been only 

 partly effective. Disinfection by acid or copper sulphate is cheaper 

 than by the other methods commonly recommended. 



(5) In addition to decreasing damping-off after the seedlings 

 come up, the chemical disinfectants above mentioned, when properly 

 used, cause an increase in the apparent germination and are very 

 helpful in controlling weeds. This latter effect alone at some 

 nurseries pays the entire expense of the treatment. Sulphuric acid 

 has, furthermore, at some places resulted in marked increases in the 

 late season growth of Pines. 



(6) In some soils formaldehyde kills dormant seed, and the other 

 three most satisfactory disinfectants at some nurseries kill the root 



