456 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



tony patches in wounds and, by delaying 

 the healing over process, makes a favor- 

 able place for the entrance of a parasitic 

 fungus. 



Amongst the fungi which are re- 

 sponsible for cankers in various parts of 

 the country are: Bitter Rot fungus 

 (Sphaeropsis malorum Pk.), Myxosporium 

 corticolum, Edg., Coryneum foliicolum, 

 Fckl., Phoma viali, Schulz and Sacc, 

 Cytospora Sp., European Apple Canker 

 (Nectria ditissima. Tul.) and Nummu- 

 laria discreta Tul. 



Closely associated with canker caused 

 by fungi is the killing back of small 

 branches and twigs caused by the same 

 organisms. In searching orchards for 

 cankers we have found this dying back 

 of the branches and water-sprouts much 

 the more common of the two. The 

 fruiting bodies of the same fungi have 

 been found on both, and cankers on 

 larger limbs have been found repeatedly 

 which apparently started from the dis- 

 ease following back on a smaller branch 

 or twig. Inoculations with canker pro- 

 ducing fungi early in the spring show 

 that they are capable of killing the 

 young twigs very rapidly and run back 

 a considerable distance in a single sea- 

 son. A twig blight may be caused by 

 the pear blight bacillus. 



In many ways the dying back of small 

 branches is like the development of 

 canker. The fungus may spread back 

 only a short distance each year for a 

 number of years or the spread is rapid 

 and the branch is killed back a consid- 

 erable distance in a single year. It is 

 probable that in many instances the 

 young wood is injured by freezing and 

 the fungi gain entrance in this way. We 

 have observed the same thing where 

 young nursery stock has become in- 

 fected through wounds made in cutting 

 back when set. Twigs and limbs affected 

 in this way should be cut off well below 

 the diseased portion and the wounds 

 protected from further infection. 



Sphaeropsis Canker 



The canker caused by the black rot 

 fungus, Sphaeropsis malorum Pk., is 



widely distributed. This disease is 

 known as the "New York Apple Tree 

 Canker," because it was first described 

 from New York. This fungus causes 

 the black rot of the fruit and a leaf 

 spot as well as the disease of the wood. 



See Black Rot. 



The fungus attacks either young or 

 old branches and the amount of damage 

 depends on the amount of bark and 

 adjoining surface portions of the wood 

 which is destroyed. In some cases a 

 branch may be girdled in a short time 

 and death of that branch results, but in 

 other cases the canker spreads for years 

 on one side of the branch before it is 

 completely girdled. The other side of 

 the branch in such a case may become 

 somewhat enlarged. 



To control this canker, the orchardist 

 should remove all dead branches, and 

 all old neglected trees such as one fre- 

 quently sees along the roads, and burn 

 them. Branches which show bad cankers 

 should be cut off back of the canker and 

 burned. In the case of young cankers, 

 the branch can frequently be saved by 

 cutting away the diseased tissue down 

 to healthy wood, disinfecting with a 

 solution of copper sulphate, one ounce 

 to one gallon of water, or corrosive sub- 

 limate, one part to 1,000 of water, and 

 then painting over with pure white lead 

 in boiled linseed oil or coating with a 

 good quality of grafting wax. The trees 

 should be gone over carefully a number 

 of times each year and developing 

 cankers and wounds should receive at- 

 tention. Spraying for apple scab will 

 help to control the cankers by reducing 

 the amount of material for infection and 

 by covering wounds with the fungicide. 

 All decayed fruit should be destroyed, 

 since the black rot of the fruit and this 

 canker are caused by the same fungus. 

 The treatment outlined should go far 

 toward controlling cankers caused by 

 other fungi. 



Bitter Rot Canker 



This canker is caused by the fungus 



which causes bitter rot of the fruit. On 



the dead bark the fungus produces little 



black pustules from which, when they 



