If shoots are hollow, a shoot insect may be the primary cause of shoot death. Other shoot blight fungi, such as Sirococcus , may cause symptoms similar to Diplodia . You may need to have a pest specialist determine the causal agent. Older infections may have pronounced callus growth around canker edges. The top of the tree above girdling cankers is dead.
Symptoms first appear in mid-summer.
Pycnidia are found at the root collar. Any standard mycological media, such as malt or potato dextrose agar, may be used to isolate Diplodia . The fungus grows rapidly. Diplodia does not sporulate readily in culture. To produce spores for positive identification, place sterile pine needles over actively growing cultures and incubate in light.