I noticed that my plum tree has a 4 inch crack in its bark (on its trunk) that is open and brown. There are no insects that I can see, what do I do? I wondered if I scrape out the brown and spray with wound sealer. Think it would work? I cannot lose this tree. Help.

tamara, i'd just measure it, (use masking tape or a paint pen to mark the size) and then just observe. if there is no insects and no mold or other fungi growing in it, it may have already healed itself.

Please check also these links:

American Plum Borer

and

Peach Tree Borer