SEED TESTING 53 



Treating the soil with 1-50 formalin at the rate of two quarts to 

 the square foot of soil, will kill damping-off fungi, and will hence 

 effectually prevent the malady under the most favorable weather 

 conditions for fungous growth. Formalin soil treatment is also 

 somewhat beneficial in stimulating plant growth and in killing some 

 weed seeds. The chief objections are the cost, the time required 

 for it to act, and for the soil to dry out. 



[If the fungus gets into the cutting or seedling bed it may be 

 checked more or less by withholding water and allowing the sun to 

 reach the sand or soil of the bed.] 



80. Sterilization of the soil by heat has proved most satisfactory 

 from all standpoints, except that under certain conditions it may be 

 more expensive than formalin. Steam sterilization by the "inverted 

 pan" method is especially recommended where a steam traction 

 engine is available. [The temperature of the soil should reach 210 

 degrees at the bottom of the bed for at least 30 minutes.] 



Aside from preventing damping-off several beneficial secondary 

 effects may follow; for instance, killing of weed seeds and insect 

 pests, and greatly increased size and vigor of plant growth. As 

 a cultural control growers should avoid infected, poorly drained 

 soils and thick sowing of seed. The only means of checking the 

 disease after it has started is to remove the covers in order to 

 reduce the temperature and the moisture of the soil and of the air 

 immediately above the plants. 



The United States Department of Agriculture secured best re- 

 sults in treating soil for damping-off of coniferous seedlings by 

 drenching with dilute sulphuric acid (one ounce to one gallon) 

 several days before seed sowing and a week after the seedlings 

 appeared, "in December there was a fine stand of healthy seedlings 

 on the treated plot and the soil was free from algae and moss, while 

 the check plat was green with algae and moss and there were prac- 

 tically no seedlings left. Only Norway spruce seemed to suffer. 

 For this plant a weaker solution (1 part to 500) is recommended. 



According to another source, damping-off may be prevented by 

 "treating the soil with dilute iron or copper sulphate." 



81. Pricking out (or off) is a ga/dener's term for trans- 

 planting seedlings while yet so small they can easily be 

 lifted on a stick scarcely wider than a toothpick at its 

 sharpened end. A better form consists of two points 

 which form a blunt V. The seedlings are thus moved 

 from the seed pans and placed in other flats at greater 

 distances apart, say an inch, until better rooted. Prick- 

 ing out is done also to avoid risk of damping-off (78). 



