372 MAINE AGRICULTURAL EXPERIMENT STATION. IQIO, 



short distance each year for a number of years or, as indicated 

 above, the spread is rapid and the branch is killed back a con- 

 siderable 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 infected 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 farther infection. 



Sphaeropsis canker. The canker caused by the black rot fun- 

 gus, Sphaeropsis malorum Pk., is widely distributed in Maine. 

 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. 



The appearance of different early stages of cankers caused by 

 this fungus is shown in Figs. 257, 258 and 259. The dark 

 colored, cracked bark of the older, central parts, some of the 

 small, black pycnidia or spore bearing bodies, and the crack 

 between the healthy and diseased bark are shown in Fig. 257. 

 This also shows, somewhat indistinctly, where cracks have 

 formed between the healthy and diseased bark at the end of 

 each growing season for at least 3 years. In this and in Figs. 

 258 and 259 infection probably took place on a smaller twig or 

 branch and followed back to the larger branch as suggested by 

 the small, dead stubs. It is not always possible to see the extent 

 of each season's growth on account of other fungi and lichens 

 growing over the dead bark. 



The fungus attacks either young or old branches and the 

 amount of damage depends on the amount of bark and adjoin- 

 ing 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 



* The manner in which young twigs and fruit-spurs become infected 

 by fungi is a matter which needs farther investigation. 

 ** Paddock, Wendell, N. Y. Exp. Sta. Bui. 163, 1899- 



