April, 1912.] SOME APPLE DISEASES — TREATMENT. 



17 



BLACK ROT, CANKER AND LEAF SPOT. 



Sphoeropsis Malorum Berk. 



The three diseases given above have been found to be due to a 

 single fungus, ^'Sphoeropsis Malorum." The black rot of the 

 apple is very common in New Hampshire. It is dark brown or 

 black in color and the affected tissue comparatively firm. It is 

 thus readily distinguished from the soft rots. It may start on 

 any part of the fruit, but often begins at the blossom and fre- 

 quently follows insect stings. The disease is primarily a rot of 

 ripe fruit, but it may often be 

 found as dark brown spots 1-8 to 

 1-2 inch in diameter several weeks 

 before the apples are mature. 

 These spots may develop very 

 slowly until about picking time, 

 but after that spread rapidly, in- 

 volving the whole apple. As the 

 rot develops, numerous minute, 

 black elevations may be seen on 

 the apple (Fig. 20). These are the 

 spore producing bodies of the 

 fungus and are known as pycnidia. 

 The rot does considerable damage 

 in cellar storage, but is especially 

 common on the .fruit left on the 

 trees or ground. This worthless 

 fruit becomes a source of infection the following spring. 



Canker is a term applied to rough, unsightly wounds that are 

 known to be due to the action of fungi. The most common 

 variety of this trouble in New Hampshire is the "black rot 

 canker," also known as the "New York apple tree canker." ^ 

 Both large and small limbs are attacked and sometimes the trunk. 

 In some cases it seems to cause merely a greater roughening of 

 the bark, but where a broken twig or other injury furnishes an 

 entrance to the actively growing tissue of the host the effects 



Fig. 20. — Black Rot of apple due to 

 Sphoeropsis Mahriim. 



1 Paddock, Wendell. The New York Apple-Tree Canker. N. Y. Agr. Exp. Sta. Bull. 16.3. 

 Paddock, Wendell, Ibid (Second Report), N. Y. Agr. Exp. Sta. Bull. 18.5. 



