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SPUR BLIGHT OF RASPBERRIES 



Daniel R. Coolcy, C. M Becker^ 

 and W. J. Manning 



Department of Plant Pathology 

 University of Massachusetts, Amherst 



Spur blight is a disease of raspberries caused by the fungus 

 Didymella applanata . The fungus infects buds, nodes and sometime: 

 the internodal regions of raspberry canes during the summer. The 

 disease surreptitiously depresses berry yields, for canes are seldom 

 Killed, yet some bearing nodes and transport tissue on each cane 

 may be destroyed. Serious epidemics can reduce yields by 30%, 

 though light infections may not depress yields at all. It is'also 

 thought that spur blight makes canes more susceptible to winter 

 injury . 



Symptoms 



Spur blight first appears on new canes, usually near the base, 

 m late spring or early summer. In Massachusetts, the first lesions 

 should appear in June. Brown or purplish soots develop around areas 

 where leaves are or were attached. These spots may enlarge to cover 

 the cane for 4 or 5 inches, but usually lesions are limited to an 

 area around the leaf petiole. These lesions turn to gray areas with 

 tiny black spots on the cane in the second (fruiting) year. Buds in 

 the affected area are weak, and some buds fail to develop at all. 

 Laterals in the area are weak and yellowed, and may wither and die. 



The grey lesions are similar to those caused by another disease, 

 anthracnose. However, anthracnose has a characteristic bulls-eye 

 pattern of dark rings in the lesion. Spur blight lesions are more 

 scattered, and are almost always associated with leaf nodes. 



Disease Cycle 



The spur blight fungus produces two similar kinds of fruiting 

 bodies. These occur together on lesions. There are differences in 

 the length of time during which each type of fruiting body releases 

 spores. However, spores of one type or the other are present from 

 early spring to late fall. 



One type of spore is called an ascospore, which is produced in 

 a fungal fruiting structure called a perithecium. Perithecia are 

 found in lesions on second year canes. The majority of ascospores 

 are released when new canes are emerging in April or May. The spores 

 are released largely during and after rain, though low levels may 

 be released by dew. Most ascospores are released by the end of 

 June. While these spores cause new infections on first year canes, 

 they do not cause all primary infections, and they are not the only 

 type of overwintering spore. 



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Extension Technician "^Research Assistant Professor of Plant Patholog 

 The authors would like to thank Paula Saucier for the illustration, 

 and Dr. William Lord for advice on pruning techniques. 



