Growth and advancement of the canker in the larger branch generally is very slow. Improper pruning can greatly increase the number of cankers on susceptible shrubs and trees. Fungal cankers usually begin as infections at twig and branch stubs left from breakage or as pruning wounds. The fungus moves into the larger branch or trunk at the junction with the stub. Large cankers on trunks weaken them structurally.
Strong winds are likely to topple a cankered tree by breaking it over at the canker site.
Branches with cankers should be pruned out when cankers are still small.