Red oak has black “stain”


We live in the beaches and have a massive red oak tree. It’s about 127 inches circumference. It’s surrounded by Baltic ivy and a bit has grown up the base. When clipping that off we found two “ gashes” near the base of black. Those are about 14 in long and 2 in wide. They are mostly dry. But there is a little bit of gummy tarry liquid. Is this something to worry about?


Thank you for reaching out to Toronto Master Gardeners in regard to the state of your red oak tree. It is difficult to be precise given the picture which you have submitted. That being said, this is what may be going on with your tree.

Phytophthora rot, a fungal disease that affects oak trees, is a disease that occurs in oak trees. The disease can cause black staining on the trunk and branches of the infected tree, rendering it inoperable. Tree dieback, leaf yellowing, and tree color loss in the summer are all signs of a disease that has caused a tree to die. Trees that have been weakened by drought stress, have been wounded, or have been injured during a storm are more likely to develop Phytophthora rot. There is no cure for Phytophthora rot. It is important to prevent it from spreading.

The link below provides additional information on red oak diseases.

You may wish to consult a certified arborist about the health of your tree. To find a certified professional arborist to help you, visit the International Society of Arboriculture’s searchable database here.

We wish you every success in treating your tree.