i88 



Bulletin 236. 



Hoiv this Canker Differs from the Well Kiiozvii Nezu York Apple Tree 



Canker 



The New York apple tree canker (Fig. 62) described by Paddock^*" 

 in Bulletins No. 163 and No. 185 of the New York (Geneva) State 

 Experiment Station, is very abundant and destructive in many orchards 

 of the State. It is caused by a fungus and is in most respects very differ- 

 ent from the blight canker with which, nevertheless, it is frequently con- 

 fused. The chief differences between the two are set forth in the follow- 

 ing parallel columns : 



New York Apple Tree Canker 



Caused by a fungus. 

 Usually found on ihe main limbs of old 

 trees. 



Diseased portion more or less szcoUcii, 

 cracked and 1 oughciicd. (Fig. 62.) 



Cankered surface black. 



Covered with minute black pimples — the 

 fruit bodies of the fungus often not so 

 evident in old cankers. (Fig. 62.) 



Freshly cankered tissue dry. 



Cankers perennial, i. c, living over and 

 spreading from year to year. 



Blight Canker 



Caused by bacteria. 



Occurring most frequently on the body 



and limbs of young trees just coming 



into bearing. 

 Diseased area sunken and smooth not 



cracked and cliecked. (Fig. 53.) 

 Cankered surface brozcn. 

 A'ot showing any pimples or fungus fruit 



bodies, except in old cankers tliat have 



been invaded by saprophytic forms. 

 Freshly cankered tissue n.'atery. 

 A large per cent of the cankers active 



but one season. 



3. How THE Disease Affects the Tree 



The effect of the canker on the tree is to lower its vitality to a greater 

 or less degree by cutting off the food supply to the roots, and thus indi- 

 rectly reducing the flow of sap to the branches and leaves. In other words, 

 it acts the same as partial or complete "girdling." The "collar rot" antl 

 " crotch cankers " seem to Ijc the most fatal to the tree. The effects of 

 the canker are first evidenced in the foliage. If there is a large body 

 canker, the entire tree may show the effects of the trouble. More often the 

 first symptom noted by the grower is the peculiar appearance of the foli- 

 age on one or more of the limbs. Either these branches fail to leaf out at 

 all in the spring, or if they do the leaves never fully expand but remain 

 undersized and curled or inrolled. They never take on the dark green 

 color of healthy foliage, but remain pale and gray. Growers often refer 

 to such trees as having " mouSe ear " leaves. As the season advances and 



