February, 1915 



THE CANADIAN HORTICULTURIST 



31 



Peach Canker* 



W. A. McCubbin, St. Catharines, Ont. 



IN order to add the weight of experi- 

 mental evidence to these observations 

 work has been carried on during the 

 last two years by the writer with the 

 object of finding out by the culture me- 

 thod what fungi were present in active 

 cankers and to determine by inoculation 

 whether any of these were capable of 

 forming cankers in healthy limbs. The 

 account of this work is to long to be 

 given here, but will be published later 

 in bulletin form. Briefly, of the half- 

 dozen fungi obtained from cankers only 

 one occurred with any frequency, and it 

 was apparently the Cytospora already 

 mentioned. This was then inoculated in- 

 to peach limbs. At the same time two or 

 three of the other cultures were also 

 used for inoculation, as well as the 

 Brown Rot fungus obtained from rot- 

 ting peaches. 



.4s was expected, only the two, the 

 Brown Rot and the Cytospora, showed 

 a clear and unmistakeable power to in- 

 duce canker conditions in the limbs, i.e., 

 they killed the tissue about the point of 

 inoculation, set up a copious gum flow, 

 and stimulated a pronounced callus 

 growth around the wound. 



CAUSE ESTABLISHED 



It would seem then that the cause of 

 canker is fairly well established to be 

 due to either or both of the two fungi 

 mentioned. It still remains to account 

 for the enlargement or extension of the 

 canker from year to year. There is a 

 good deal of evidence which goes to 

 show that while a canker may be start- 

 ed by one of these fungi, neither is like- 

 ly to extend it after the first year unless 

 the surrounding tissue is first weakened 

 in some way. And the only reasonable 

 explanation which will account for such 

 weakening is that the callus around the 

 incipient canker is stimulated by the 

 presence or by the action of the fungus 

 into late and abnormal growth, and 

 hence entering the winter in^ an unrip- 

 ened condition is killed by winter cold. 

 The fungus is then able to invade the 

 injured area and the canker spreads. 

 The mass of evidence which can be 

 brought forward to support this view is 

 large and will have to be given in detail 

 elsewhere, but I believe that the freez- 

 ing of the immature callus is a very im- 

 portant factor in the enlargement of 

 cankers on the peach. 



In order to prove beyond question the 

 possibility of this process of canker for- 

 mation, I froze some three or four can- 

 kers in late summer (September 17) with 

 artificial cold, using a cylinder of carbon 

 dioxide for the purpose. In each case 

 the tissue was de stroyed and a callus 

 •Continued from December issue. 



has since formed at the edge of the dead 

 area. 



According to the evidence in hand at 

 present, the process of canker forma- 

 tion may be summed up as follows : 



A fungus (either Brown Rot or Cytos- 

 pora) establishes itself in a dead or dy- 

 ing twig, a wound, crack, or borer hole, 

 and kills a small area of the living tissue. 

 There is a stimulation of the healthy 

 tissue around this area which results in 

 the formation of an excessive callus 

 growth. This callus enters the winter in 

 an unripened condition and is killed by 

 freezing. In the following spring the 

 frozen area is invaded by the fungus, 

 and the process is repeated. 



It is possible that with further study 

 some slight modification may have to be 

 made in this conception of the origin 

 and spread of Peach Canker, but at pre- 

 sent it seems to fit without any disagree- 

 ment all the facts known to me. 



PREVENTION AND CURE 



I am unable to state definitely what 

 proportion of our cankers is due to each 

 of the fungi mentioned but I think I am 

 safe in saying that far the greatest num- 

 ber arise from twigs killed by Cytospora. 

 In dealing with this fungus as well as 

 with Brown Rot, it must be remember- 

 ed that though the spring spray will de- 

 stroy all surface spores it will unfortun- 

 ately not reach the fungus in its habitat 

 under the dead bark. It remains here 

 imhurt and forms countless spores in the 

 minute pimply pustules which may be 

 seen on almost any dead peach limb. It 

 is necessary then in clearing an orchard 



of this fungus, to get rid of all dead 

 twigs and branches as soon as possible. 

 In the same way no Brown Rot or mum- 

 mied peaches should be allowed to re- 

 main on the branches. A little extra 

 care will be needed at pruning time to 

 effect this result. 



In the light of what has already been 

 said regarding the cause of canker, and 

 the treatment of cankers already formed 

 can be outlined with some confidence. 



It would be absurd of course to try to 

 treat cankers on the smaller limbs, but 

 where a canker involves a trunk or main 

 limbs it is well worth while to get it to 

 heal up. The main object is to put the 

 canker into such a shape that the callus 

 around it will grow sufficiently hard and 

 mature to resist the winter. The best 

 way to do this is to clean out all the 

 gum, dead wood, and bark, to allow ac- 

 cess of the sun and air, and to keep it 

 as dry as possible. After a rain is a 

 good time to do this, as the gum is then 

 soft, and it should be done early enough 

 in summer so that the wood will ripen 

 before fall. After cleaning it is well to 

 wash or brush out the canker with an 

 antiseptic solution (corrosive sublimate 

 I -1000) and when dry to give it a coat of 

 ordinary lead paint. The corrosive sub- 

 limate destroys all fungi in and about the 

 canker and the paint prevents them from 

 invading and rotting the dead heart wood 

 afterwards. 



,This treatment costs for labor and 

 material about five cents a canker, and 

 has given excellent results in the experi- 

 mental work carried on during the last 

 three years by the writer, as well as in 

 actual practice by some of the Niagara 

 peach growers themselves. 



During the "Ap:)le Week" campaijrn conducted 

 fo increase the consumption of apples, prizes w 

 by grocers and dealers in the market. The illus 



the city 

 1 



recently in Vancouver and other wcetern cities 

 ere offered for the best display of applefl made 

 tration shows the flret prize exhibit made in 

 market. 



