14- 



DHFOLIATION BY GYPSY MOTHS PREDISPOSES YOUNG APPLE TRTiES 



TO CANKER AND DIEBACK 



1 2 



Christoper M. Becker and V>filliam J. Manning 



Department of Plant Pathology 



Canker and dieback diseases were unusually prevalent on apple 

 trees of all ages in Massachusetts in 1981. The fungi that causes 

 these diseases are weak pathogens that usually infect and cause 

 disease only on trees weakened by various stress factors, such as 

 drought, winter injury, etc. 



Cold temperature injury from the previous winter seemed to 

 have weakened a number of young trees. Sunken cankers were noted 

 at the origin of young branches on trunks (see Figure 1). 

 The young branches were often girdled 

 and dieback resulted by late June or 

 early July. In other cases, dark 

 sunken lesions developed near branch 

 tips, resulting in dieback of new 

 shoots. The canker- causing fungus 

 Nectr ia isfas usually associated with 

 these dieback problems. 



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1 



Apple Pest Management Technician 



Fig. 1. C ytospora canker 

 on 3-year-old Red Delicious 

 following severe defoliation 

 ^y gypsy motli caterpillars. 



Professor of Plant Pathology 



