414 AGRICULTURE OF MAINE. 



is rather uncommon in Maine. Moreover the entire absence 

 of the characteristic "fire Wight" has been noted repeatedly on 

 pear trees growing within and alongside of apple orchards af- 

 fected with the fungous twig blight. 



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, 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 ofif 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 IMaine. 

 This disease is knowu 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. 74, 75 and 76. 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. 74. This also 

 shows, somewhat indistinctly, where cracks have formed be- 

 tween the healthy and diseased bark at the end of each growing 

 season for at least 3 years. In this and in Figs. 75 and 76 

 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 



*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. 



