Treating Cut Areas - Do not paint wounds.
When cuts are made properly at the branch bark ridge, trees are able to compartmentalize, or set boundaries, at the injury (pruning) site. This process helps resist the spread of infection. Trees can resist the spread of microorganisms if they are fast and effective in setting the boundary defense system, but some are fast and others slow at this process.
No matter how efficiently or inefficiently the tree sets boundaries, wound dressings do not stop decay and actually increase the rate of decay. Therefore, it is not necessary to paint wounds once a cut is made. Rather, leave the tree to its own defenses.
A good reference is Purdue University Cooperative Extension publication: Pruning Ornamental Trees and Shrubs
