Notes on Nut Diseases
Sweet Chestnut Blight
Identification
The fungus Cryphonectria parasitica causes sweet chestnut blight.
This canker-forming fungus causes lesions on branches or stems. Sunken
orange cankers grow and increase in diameter each year until the trunk
or branch is completely girdled. On other tree species, such as oaks and
hickories, the fungus seems to be purely saprophytic, feeding on wood
that is already dead. In the genus Castanea (sweet chestnut) the fungus
is parasitic by first killing live wood and then digesting the killed
tissue.
Period of activity
Chestnut blight overwinters in cankers from previous infections. It
produces two types of spores. Sexual ascospores are spread by wind and
produced in small perithecia on the bark surface. Asexual spores called
conidia are also produced in larger cankers and are present in sticky
orange tendrils that ooze from small bodies called pycnidia. Insects,
birds and animals that come into contact with the sticky ooze most often
spread conidia.
Management
There are no chemical controls registered to manage sweet chestnut blight.
Research focuses on breeding for partially resistant or immune cultivars.
Immune cultivars are not available.
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