Page 26 



BETTER FRUIT 



April 



mersed in the cyanide of mercury 

 (1 to 500) solution. A cut was then 

 made with this knife through the bark 

 and cambium of a clean, healthy pear 

 branch. This operation was repeated 

 many times, treating the knife with a 

 drop of ooze and immersing it in the 

 disinfectant each time before a new cut 

 was made. In most of the cuts no blight 

 developed, but in a small percentage of 

 cases the disease did develop. It is evi- 

 dent that this disinfectant is not a safe 

 one to use on tools. This is unfortunate 

 but nevertheless true. 



Another surprising and remarkable 

 result was obtained with corrosive sub- 

 limate (bichloride of mercury) as a 

 disinfectant for metal tools. The above 

 experiment was duplicated, using cor- 

 rosive sublimate at a strength of 1 to 

 500 as the disinfectant. Not a single 

 case of blight developed where this 

 material was used. 



To summarize: Cyanide of mercury 

 1 to 500 is effective on the wounds, but 

 not effective on metal tools; and cor- 

 rosive sublimate is not effective on the 

 wounds but effective on the tools. 



It is evident that if the cyanide of 

 mercury is applied to every wound — 

 whether a wound from which blight 

 has been cut or simply a wound made 

 in healthy bark in probing for blight — 

 it will prove effective. In other words, 

 it will destroy blight bacteria left on 

 the surface of the wound by the tools. 

 If the blight cutter wants to disinfect 

 his tools also, and this is preferable, he 

 should use the corrosive sublimate for 

 that purpose; and the cyanide of mer- 



cury for the wounds. While this pro- 

 cedure will prove thoroughly effective, 

 the carrying and use of two solutions is 

 cumbersome and not relished by the 

 average blight cutter. 



It is evident that another disinfect- 

 ant should be found which will be 

 effective on both the wounds and the 

 tools. A search is now being made for 

 such a disinfectant. 



It is interesting to speculate on why 

 the cyanide of mercury is effective on 

 the wounds but not on the knife, while 

 the opposite is true of the corrosive 

 sublimate. The following suggestions 

 are worth considering in this connec- 

 tion: The cyanide of mercury may 

 form a chemical compound with the 

 metal when placed on tools, which de- 

 stroys its effectiveness as a disinfect- 

 ant. Or it may be effective on the 

 wound simply because it modifies the 

 plant tissues — by injury or otherwise — 

 making it impossible for the bacteria to 

 develop and enter the normal tissues 

 beyond. The corrosive sublimate, as 

 has already been discussed, probably 

 becomes ineffective in the presence of 

 the organic matter in the wound. On 

 metal tools, in the absence of organic 

 matter, it is effective. 



A Prominent Disinfectant 



In our experiments a number of dis- 

 infectants have been tried, and most of 

 them have proved ineffective. With 

 some, unfortunately, not sufficient work 

 has been done to draw final conclu- 

 sions. One of these appears quite 

 promising and is well worthy of fur- 



ther work. This is formaldehyde, also 

 known as formalin. 



Experiments have been conducted to 

 determine the value of formaldehyde 

 as a disinfectant for both the wounds 

 and tools. It was used at strengths of 

 4, 7 and 10 per cent. In these tests the 

 4 per cent strength proved effective in 

 all cases as a disinfectant for the tools. 

 The other strengths were not tried on 

 the tools, but undoubtedly the 7 and 10 

 per cent would be effective. 



All of these strengths were tried on 

 the wounds of pear trees. The 4 per 

 cent and 7 per cent strengths proved 

 effective in many cases, but developed 

 blight in a few cases. Hence these 

 strengths cannot be recommended. The 

 10 per cent strength has proved 

 effective in all these tests; as not a 

 single case of blight has developed 

 where this strength was used. Wounds 

 treated with corrosive sublimate at the 

 same time developed the disease. 



These tests with formaldehyde were 

 not started until midsummer, hence the 

 results cannot be considered final. It 

 is well known that a pear tree usually 

 will not blight as readily after mid- 

 summer as during the spring and early 

 summer, due to the great amount of 

 sap and more succulent growth early in 

 the season. Next season we shall repeat 

 the experiment at tlie most critical 

 time, and I reserve final conclusions 

 until that time. 



While the findings cannot be consid- 

 ered final, the writer considers formal- 

 dehyde as an extremely promising dis- 

 infectant for blight-control work. If it 

 proves effective during the most critical 



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