100 



later it cracks away, exposing the wood. (Fig. 16.) A badly 

 cankered limb bears other evidence in the form of yellow 

 leaves, and where the limb is completely girdled the leaves 

 above become yellow, then brown and the bark and fruit 

 shrivel. 



Bitter-Rot Canker. 



This canker is caused by the same fiingus as bitter-rot of 

 the fruit. It is similar to the black-rot canker, but usually 

 the diseased bark becomes much cracked and remains clinging 

 to the wood. It is much less common in this State than black- 

 rot canker. 



European Canker. 



This is probably the most destructive of fruit diseases in 

 Europe. In Massachusetts, however, it cannot be considered 

 serious. The causal fungus, Nectria ditissima, probably in 

 most cases gains entrance to the host tissues through wounds. 

 Both young and old limbs are attacked, and frequently these 

 cankers follow hail injury. 



Nectria-canker usually takes the form of an open wound, 

 which is accompanied by swelling of the surrounding live 

 tissue. Zones or folds of tissue border the wound, and these 

 distinguish this canker from all others. Crotch infections are 

 not unusual. Types of Nectria-canker are shown in Fig. 17. 



Nail-Head Canker. 



This is the least important of the cankers occurring in the 

 State, and it has only recently been found within our borders. 

 It is a serious disease in the Mississippi Valley, but is not 

 likely to become common here. The cause is a fungus, Num- 

 mularia discreta. 



In a general way, the treatment for all cankers is the same. 

 It consists chiefly in cutting out and disinfecting wounds. 

 Infected twigs and small branches should be pruned off where 

 this will not materially injure the tree. On large branches 

 and trunks, cankers should be cut out, using the utmost care 

 to remove all diseased tissue down to the healthy wood and back 

 into the healthy, living bark. Where possible, the wound thus 

 made should be shaped with a sharp point at each end and 



