358 SEEDING AND PLANTING 



Damping-off is a universal trouble in seedbeds of all kinds. 

 There is no positive means of control which will invariably and 

 under all conditions check the disease after it has become fully 

 established. It is especially difficult to check in coniferous seed- 

 beds because the plants are so close together that the disease quickly 

 spreads from one to another. Furthermore, weather conditions 

 which aggravate the disease cannot be overcome in the open air. 

 The disease sometimes kills the seedlings before they are above 

 ground. More often it first appears a few days after they are 

 up and continues for several weeks or while the stems are soft 

 and succulent. The trouble usually ceases after the stems become 

 woody. The fungus present in the soil makes its way through the 

 epidermis into the tender stems of the seedlings at the surface of 

 the soil or in the roots immediately below the surface. It first 

 appears on the stem as a small watery spot. It develops rapidly 

 and in a day or two so weakens the plant that it usually falls 

 over and soon withers and dies. If weather conditions are unfav- 

 orable all the seedlings may be destroyed within a week after 

 germinating. Usually, however, some survive in patches over 

 the seedbeds. Under more favorable weather conditions only a 

 few plants here and there become diseased. 



Damping-off fungi are nearly always present in ordinary nursery 

 soils. The various methods practiced to prevent or overcome 

 injury relate to the following: 



a. Partial or complete sterilization of the soil prior to seeding. 



b. Attaining conditions in the seedbeds inimical to the rapid 

 development of the fungi. 



Steam sterilization by the inverted pan method by which the 

 soil in the seedbeds is subjected to steam under pressure for sev- 

 eral hours was tested by Gifford and found only partially effective, 

 as the soil becomes rapidly reinfested after heating. Gifford 1 

 secured excellent results by disinfecting the beds with formalin 

 several days before sowing the seed. The solution used was 1 

 part commercial formalin (40 per cent formaldehyde gas in water) 

 and 100 to 200 parts water. It was applied at the rate of 1^ gallons 

 per square foot of seedbed. Formalin will often kill the seed if 

 applied at the time of seeding. When applied several days prior 

 to seeding repeated experiments have shown no perceptible injury. 



1 Gifford, C. M.: The damping-off of coniferous seedlings. (Vermont 

 Agri. Exp. Sta., Bui. 157, p. 156. 1911.) 



