THE FOREST NURSERY 359 



Spaulding obtained excellent results by treating the beds with 

 formalin before seeding. He has also successfully used zinc chlo- 

 ride and copper sulphate on alkaline soils. He has also found 

 sulphuric acid an excellent general disinfectant against damping- 

 off fungi when used with adequate precautions. All of these fun- 

 gicides appear to leave a residue in the soil which protects against 

 reinfection. 



In the sulphuric acid treatment the seedbeds are thoroughly 

 soaked with the chemical, applying it at the rate of fV ounce per 

 square foot of seedbed in from 300 to 500 times the volume of 

 water depending upon the character of the soil. Strongly 

 alkaline soils require more disinfectant per square foot than 

 acid soils. Soils subject to rapid drying in the surface layers 

 should receive much less than soils that remain moist. Sul- 

 phuric acid seriously injures the germinating seedlings when it is 

 permitted to become concentrated through the drying of the surface 

 soil during the period of germination. Hartley recommends its 

 use only when the nurseryman knows how to recognize and pre- 

 vent injury. As the injury is always due to the concentration 

 of the acid in the surface soil consequent to capillary action and 

 evaporation, it can be prevented by keeping the beds uniformly 

 moist during germination and for a period of 3 to 6 weeks following. 

 The serious injury or destruction of the plants by sulphuric acid 

 when the soil moisture is not under perfect control is so certain that 

 the author recommends the formalin treatment as a more practical 

 and safer method of preventing damping-off by soil sterilization. 



Attaining conditions in the seedbed by cultural methods inimi- 

 cal to the rapid development of damping-off fungi is often more 

 practical and less expensive than the sterilization of the soil by 

 heat or chemicals. The sowing of the seedbeds in the autumn 

 or early spring is usually much less favorable to the development 

 of damping-off fungi than sowing in late spring or early summer. 

 Intelligent control of irrigation and shading greatly reduces the 

 loss from damping-off. The beds should not be kept overwet 

 and the shade cover should be removed at night and during 

 cloudy weather, particularly if the weather is warm and moist. 

 The quality of the seed has a marked influence on the disease. 

 Poor seed is more irregular in germination and produces seedlings 

 of weak vitality. Hence, the seedbeds are subject to injury for a 

 longer period and the plants are much less resistant. 



