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MASS. EXPERIMENT STATION BULLETIN 351 



to breathe then formaldehyde and, in well-ventilated greenhouses, it can be used 

 with less injury near plants. In the work of Yu (102), acetic acid 1.5 percent was 

 also less injurious to germination of cucumber than was formaldehyde 1:50, 

 with both applied 9 days or more before seeding. Since its merits were first 

 pointed out, other investigators have used it with good results. (See Table 4.) 



It is of interest to note, however, that Christoff (18), using a 1.0 percent solu- 

 tion, controlled damping-off of conifers more completely in an acid than in a 

 highly alkaline soil; but with the latter, the writer has had no experience. 



Table 4. — Results of Other Investigators with Acetic Acid as a 

 Soil Disinfectant 



Acetic acid 1.0 or 1.5 percent (approximately) may be made by diluting glacial 

 acetic acid 1.0 or 1.5 gallons to total 100 gallons. Two quarts of these dilutions 

 per square foot cannot be applied less than one week before seeding without injury 

 to some species; for example, foxglove, sweet pea, and beet. Cucumber is more 

 tolerant. A 1.5 percent solution applied 10 days before seeding was harmless to 

 these species and to Veronica repens, Cheiranthus Allionii, and Lilium philippin- 

 ense. All damping-off was prevented, germination was improved, and, because of 

 infection by Rhizoctonia in checks, growth was improved. 



The effect of acetic acid on the pH value of treated soil does not usually last 

 more than two or three weeks. 



A principal objection to acetic acid, as to formaldehyde, thus used is the delay 

 of a week or two before seeding and this, in the case of formaldehyde, has been 

 overcome by the use of the dust. Guterman and Massey (40) were equally suc- 

 cessful in using a small quantity of formaldehyde (about 7 cc. per square foot in 

 5 times that volume of water) 12 to 24 hours before seeding, the soil being then 

 well watered. 



Acetic acid 80 percent, 8 cc. per square foot, thus diluted and mixed with soil 

 did not injure Torenia, Verbena, Calendula, cabbage, and pepper and it did 

 improve their germination without, however, preventing all damping-off. 



