DISEASES OF THE APPLE TREE ] 275 



DISEASES. 



One of the worst parasites is Nectria ditissima Tul. 

 which is a frequent cause of canker in this, as well in 

 other fruit trees in continental orchards. Here it is 

 still unknown and its early detection and treatment, 

 should it find its way to our orchards, are therefore 

 important as a preventive measure. The fungus makes 

 its home on the stem or on the branches, preferably 

 at the point of insertion of a side-branch or twig, 

 which is killed immediately. The infected spots 

 assume a dark cankerous appearance, the wood is 

 laid bare and becomes 'dark brown or black surrounded 

 by the thickened and rotten edges of the bark, upon 

 which early in autumn are produced the fructifications 

 of the fungus in the shape of small red protuberances. 

 The diseased branch should be cut back down to the 

 healthy wood and burned. If the fungus attacks the 

 stem and it is not desired to lose the tree, the canker 

 should be scooped out until the healthy wood is reached, 

 and the wound is washed with a strong solution of sul- 

 phate of copper, and when dry painted over with tar. 



Fusicladium dendriticum Fckl. and F. Pirinum 

 Fckl. attack the twigs and branches, the leaves and the 

 fruit in the same way as the pear, but the leaves and the 

 fruit of the apple are here much less liable to these 

 diseases than the leaves and fruit of the pear. The 

 characteristic ash-grey blisters often appear on the young 

 twigs when yet in leaf, and the black powdery mass of 

 tissues under the blisters of the bark is more evident in 

 the apple than in the pear. These diseased twigs should 

 be carefully collected and burned. When an apple tree 

 is badly attacked by these fungi it is a sign that the tree 

 does not agree with the soil or with the situation, 



Sphaerella sentina Fckl. produces on the leaves 

 white spots edged with brown. Leptosphaeria pomona 

 Sacc. produces in upper Italy spots of a similar appear- 

 ance but of a grey colour, and Sphaerella Pomi Sacc. 



