Although, cankers are unsightly, most will not kill a tree. The term " canker" is used to describe a killed area or blister on the bark, a branch or the trunk of an infected tree.The Morton Arboretum describes it as a canker that is "usually oval to elongate, but can vary in size and shape." I have a maple tree that's been in the ground about 5 years. On older trees, a perennial canker forms. Nectria rarely kills older, established trees. Treatment. This is a very slow growing disease. Eutypella canker is common on maple trees in landscape plantings and in natural areas. The bacteria overwinter in active cankers, in infected buds and on the surface of infected and healthy trees and weeds. About 21/2 years ago it started oozing a brown substance from the trunk. Small trees that are less than 4 inches in diameter are commonly killed when the canker girdles the main trunk. Bacterial canker infections occur during fall, winter and early spring (during cool, wet weather) and are spread by rain or water, and pruning tools. Since then, she has kept records of all the reported new cases of this disease. Most are able to fend off the fungus and form the characteristic calluses. (the trunk is split I assume from the oozing). Asked January 20, 2019, 11:51 PM EST. There is no chemical preventative or treatment for most types of cankers. In 1999, a canker disease showing bleeding and oozing black sap, symptomatically similar to sudden oak death, was first noticed on a mature silver maple tree in Reno, Nevada by Leslie Lyles. Maple trees are susceptible to numerous fungal diseases that cause cankers--areas of dead bark--on tree trunks and branches. It started at the bottom ground level and it is now three quarters up the tree. By 2002, more than 20 mature silver maple trees had been reported Nectria Canker Treatment. Cankers will often appear as a swelling surrounding a sunken lesion on the bark of trunks and branches. Bleeding Canker on Maple Tree. Prune flowering trees during blooming when wounds heal fastest. Limbs and branches with cankers should be pruned back to the closest main joint. Cankers often form on the main trunk or major branches of the tree. Older trees that are not healthy may be vulnerable, but it is typically younger trees, especially those that are newly transplanted, that can be killed by nectria canker.