Lately, I have been noticing a lot of Autumn Blaze maples, also known as Freeman maples, with vertical splits or tears down the side of the trunk. The trunks look like they have been hit by a Bobcat tractor. This phenomenon, called Southwest disease, is caused by the bright winter sun warming the southwest side of the lower, unshaded, trunk.

Once the sun sets, the temperature quickly drops and the rapid change in temperature results in a vertical bark crack. The reason for the crack is that young trees lack the amount of cork cells that are found in thicker, older bark. These cork cells act as an insulating layer, reducing heat loss and buffering expansion and contraction of tissues. Most times the trees carry on just fine, closing the wound over time. On the rare occasion, tree mortality ensues.

Seams, on the other hand, not deep cracks, are also common on Freeman maples. These seams are about the thickness of a finger; it is as if a person ran one finger down the trunk and left an impression. Seams will appear on every side of the lower trunk, not just the southwest side. The seams begin as a very thin crack on the outer surface of the bark but do not continue to propagate deeper into the wood. Instead, as the trunk expands and the crack widens, a groove of bark appears between the two edges. The reason for this phenomenon is not clearly known. It might be alternating dry and wet weather during the summer that causes the trunk to expand after the bark stopped growing. Regardless, it should not be a concern to the tree or its owner.

Tips for Autumn Blaze Maple Owners:

• Do Not Apply Sealer: Do not use paint or wound dressings; these can trap moisture and increase decay.
• Keep it Healthy: Ensure the tree is properly watered during dry spells.
• Fix Girdling Roots: Check that the tree’s root flare is clearly visible. If not, it may have girdling roots that circle the trunk, which can be a major cause of stress and bark damage.
• Prevent Future Damage: Wrap the trunk with white-colored, breathable tree-wrap in the fall and remove it in early spring.  

The sparse, browning canopy in this Autumn Blaze Maple indicates the tree is dying due to Southwest Disease.

Southwest Disease is common in young Autumn Blaze maples, not so in other species.

Remarkably this tree has lost most its bark, yet the canopy still looks healthy.

Seams on the Autumn Blaze maple do not cause problems for the tree.