Pa^^c 24 



BETTER FRUIT 



April 



A New and Effective Disinfectant for Pear Blight 



IT is generally known by pear grow- 

 ers that the only way to eliminate 

 pear blight (Bacillus amylovorus) 

 from an infected tree is to cut out and 

 destroy all the infected parts of the 

 tree. It is also well known that in cut- 

 ting out and through these infected por- 

 tions often many blight bacteria are 

 smeared over the tools used in the 

 work. Furthermore, when the final 

 cuts are made in the clean, healthy bark 

 some of the bacteria on the tools again 

 are smeared over the healthy surface. 

 In many cases new infections inad- 

 vertently are made in this manner, and 

 the disease continues to spread from 

 the margins of the wound. For tliis 

 reason a disinfectant should be applied 

 to destroy any bacteria that in this 

 way may have been left on the surface 

 of the wound. The only disinfectant 

 that has been recommended generally 

 and used widely for this purpose is 

 corrosive sublimate (bichloride of mer- 

 cury). This is a very powerful disin- 

 fectant and has been extensively used 

 in the past by medical men. 



It often has been noted that where 

 the blight cankers have been removed 

 and corrosive sublimate applied, the 

 disease would continue to develop, 

 especially during favorable weather 

 conditions. This has been attributed 

 generally to a lack of thorough work, 

 leaving some blighted tissue in the 



By F. C. Reimer, Talent, Oregon 



margins of the wound. It is certain 

 that this has been responsible for such 

 continued development of pear blight in 

 very many cases. 



However, often pear blight would 

 continue to develop from such wounds 

 where the most thorough work possible 

 had been done. For this reason it was 

 suspected that possibly corrosive sub- 

 limate was not destroying all of the 

 bacteria left on such wounds. Hence 

 experiments were started in June, 1918, 

 to test the efficacy of corrosive subli- 

 mate and other chemicals as disinfect- 

 ants for pear-blight germs on the 

 wounds of pear trees. 



For the first experiment a large num- 

 ber of uniform and very vigorous three- 

 year-old Bartlett pear trees were se- 

 lected. These were entirely free from 

 pear blight at the time the experiment 

 was started. On the trunk of each tree 

 two large wounds were made by remov- 

 ing the bark and exposing the sapwood 

 over the entire wound. Blight bacteria 

 were then smeared over the surface of 

 each wound, especially over the mar- 

 gins, by which process most of the 

 bacteria were deposited on the cut sur- 

 face of the margin of each wound. In 

 order to preserve uniformity all of the 

 bacteria utilized were taken from one 

 culture. 



Immediately after placing the bacte- 

 ria the disinfectants were supplied, 



thoroughly covering the entire wound 

 by means of a new, clean, paint brush. 

 For each disinfectant a separate brush 

 was used. 



The following disinfectants were 

 used, treating with two exceptions eight 

 trees, or sixteen wounds, with each dis- 

 infectant: (1) Bordeaux paste; (2) cor- 

 rosive sublimate 1 to 500; (3) cresol 

 5 per cent; (4) cyanide of mercury 1 to 

 500; (5) lime sulphur 10 per cent; (6) 

 "Black-leak 40" 5 per cent; (7) chloro- 

 zene 1 to 500. Eight trees in which the 

 bacteria were applied to the wounds 

 but no disinfectant was used, were 

 utilized as checks. 



The results of this experiment were 

 rather startling. Every wound treated 

 with corrosive sublimate, Bordeaux 

 paste, cresol, lime-sulphur, Black-leaf 

 40 and chlorozene developed a vigor- 

 ous case of pear blight. The corrosive 

 sublimate was used twice as strong as 

 is recommended generally for this pur- 

 pose, and the brand used is manufac- 

 tured by one of the largest and best 

 known chemical firms in this country. 

 The Bordeaux paste was made by dis- 

 solving one pound of bluestone in one 

 gallon of water, and two pounds of lime 

 in one-half gallon of water, and then 

 mixing the two. The cresol used was 

 the liq. cresolis compositus. The lime- 

 sulphur was one of the best known 

 commercial brands and tested 32 de- 



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