28 MASS. EXPERIMENT STATION BULLETIN 351 



Potassium Permanganate 



This is sometimes applied to soil by British horticulturists (83, 22) with the 

 object of controlling damping-off. It is occasionally mentioned in the American 

 literature, also; and there are statements, usually without supporting evidence, 

 to the effect that potassium permanganate is a soil disinfectant. Thus Connors 

 (21) believed that its fungicidal value is known; Hunn (49) asserted that it 

 sterilizes a rooting medium (for cuttings); and Wiggin (98) was of the opinion 

 that plant propagators can check damping-ofif with it. 



Such really experimental evidence as was found in the literature points in the 

 other -direction and leads to the belief that potassium permanganate is not a 

 reliable soil disinfectant. According to McCallan and Wilcoxon (64), solutions 

 were not toxic to spores of Botrytis and Sclerotinia which were suspended in 

 them; and White (96) found it ineffective in preventing infection of cuttings by 

 Pythium. Concentrations of solutions and rates of application are variously 

 expressed, but, when translated to number of grams per square foot of soil, 

 3.5 gm. potassium permanganate did not satisfactorily protect cuttings of gera- 

 nium against Pythium (Gill, 37); Brien and Chamberlain (13) were unable to 

 protect tomatoes against Pythium by 13 gm.; 20 gm. had no apparent sterilizing 

 action on soil in Buddin's experiments (16), and failed to protect tomatoes against 

 Rhizoctonia in the work of Small (81). 



As used by the writer, potassium permanganate up to 50 gm. per square foot 

 never controlled damping-off caused by Pythium and Rhizoctonia. It is unlikely 

 that heavier applications could be used, for growth of most species was injured 

 by 50 gm., while the germination of China aster was injured by 40 gm. and that 

 of sweet pea by 30 gm. 



There was, however, improved growth of Aubrietia, holl\hock, beet, and 

 cucumber with 15 and 20 gm.; and it should be noted in this connection that 

 Webster and Robertson (94) observed marked growth response of various plants 

 to potassium permanganate. They concluded, from work with a species of Opuntia, 

 that the good effect of the permanganate on growth is not wholly, or is something 

 more than, manurial. 



Potassium permanganate, in these experiments, made a slightly' acid soil less 

 acid. Chadwick (17) concluded that the effect of this salt on the reaction of a 

 medium is not the same for all media, and his results, like those of the writer, 

 make it appear that the statement by Hunn (49) that potassium permanganate 

 acidifies a rooting medium is not always correct. 



On the basis of these results, potassium permanganate cannot be recommended 

 for the protection of seedlings against damping-off. This is not to say that it is 

 always useless in the propagation of plants vegetatively, for there is then more 

 involved than the mere prevention of damping-off and there is evidence in the 

 literature that potassium permanganate sometimes improves the rooting of 

 cuttings. Curtis (25) found that to be the case when it was applied to cuttings 

 of woody plants. Carnation cuttings rooted better when Connors (21) watered 

 the rooting medium with a solution of potassium permanganate, about 3.5 gm. 

 of the salt per square foot ; and in the experiments of Chadwick a solution of about 

 1 pound in 15 gallons, 2 quarts per square foot, improved the rooting of cuttings 

 of most species of woody plants used by him. It does not follow that potassium 

 permanganate is a soil fungicide, and the explanation of Curtis seems adequate. 

 He noted that cultures containing the permanganate were not sterile and sug- 

 gested that its beneficial effect on rooting may be due to its increasing the res- 

 piratory activity of the cutting by hastening oxidation. This view seems to be 



