36 MASS. EXPERIMENT STATION BULLETIN 351 



To lessen the cost of using soil which has been purchased already sterilized, 

 it was sometimes diluted with washed sand. Growth of seedlings was satisfactory 

 and there was no increase in damping-off. 



Increase in knowledge of better methods of using old soil disinfectants and other 

 chemicals, possible new soil disinfectants which may have more nearly ideal 

 qualities, makes it evident that a soil treatment which is good for some species of 

 plants may be not so good or even injurious to others. Thus charcoal, although 

 not a fungicide, improved the growth of nasturtium; and calcium sulfate had a 

 similar effect on sweet pea, but on sweet pea alone. 



Damping-off was not controlled by calcium sulfate, acetate, or chloride or by 

 materially raising soil pH values with hydrated lime. 



The most common evidence of stimulation of growth of plants observed 

 following the use of soil fungicides, occurred when Rhizoctonia, in untreated 

 soil, so interfered with growth that plants in treated soil, and therefore free from 

 the fungus, grew better. Exceptions are chemicals which contain nutrients as do 

 calcium cyanamide and ammonium hydroxide. 



Damping-off was well controlled by calcium cyanamide and more use might 

 well be made of it when the necessary delay between soil treatment and seeding 

 is not considered too objectionable. This is true also of ammonium hydroxide 

 which prevented damping-ofif and was, as used, harmless to most species. Ammon- 

 ium acetate was less effective. 



Ammonium thiocyanate in the soil also remained toxic to plants for too long a 

 time to be a good soil disinfectant, for there is more need of such as can be used 

 at or about the time of seeding. 



The time interval between soil treatment and seeding depends partly on the 

 species of plant involved ; and formic acid, formaldehyde, acetic acid (and vinegar) 

 were, in general, less injurious to seeds which germinate slowly than to those 

 which germinate rapidly. 



Formic acid controlled damping-off and is not ordinarily harmful if worked into 

 the soil before seeding. 



Another promising material was salicylic acid. Final stands of seedlings were 

 often much improved by it and it has the advantage of being readily applied to 

 soil without the necessity of first preparing either a solution or a dust. 



Tannic acid gave no evidence of being fungicidal, but growth of foxglove was 

 benefited and it apparently improved the soil phj'sically. 



There were indications that less of a fungicide, for example formaldehyde, is 

 necessary if not too much water is applied with it. Less than one-fifth as much 

 formaldehyde as was formerly used controlled damping-off when the quantity 

 of water used with it was also much reduced. 



Damping-off was controlled by acetic acid dusts and they were not injurious 

 to most species when applied to soil the day before seeding. Thej' were, however, 

 very toxic to softwood cuttings. 



Undiluted vinegar, applied to soil immediately before seeding, controlled 

 damping-off, usually without injury. 



Quantities of acetic acid, formaldehyde, and other volatile chemicals which 

 were safe enough if worked into the soil immediately before seeding were injurious 



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