Ask An Arborist: October 15, 2009

Mysterious Tree Damage

Image 1 Submitted by Gene Image 2 Submitted by Gene

Gene in Marietta Writes...

I live in Marietta, GA and am concerned about my Japanese maple. For some reason it appears to be losing the leaves on one side of the tree. I noticed some of the leaves curling and turning brown (like they do in the winter) about a week or so ago. The loss started on the lower limbs and seems to be moving up one side. The leaves on the opposite side of the tree appear to be just fine. I don't recall the tree losing leaves this soon before the cold weather starts. I have included the following pictures. (See above.)

And The Answer Is...

Surprisingly, we see this problem more frequently than you would think. It's obvious that the tree is receiving fairly consistent sunlight and water in its current position, but something has happened to one side. Some additional investigative work needs to be done.

First, check around the base of the tree to see if any damage has occurred on the side where the limbs are dying. If damage has occurred to the trunk or the roots on that side of the tree, the limbs on the affected side will suffer. Damage can be caused by mechanical devices such as a mower or weed whacker but since the tree is in a mulched island, this is probably unlikely. Damage could also have been caused by voles. These tiny mouse-like creatures love to chew on the base and upper roots of a wide variety of plants. By pulling the mulch and soil away from the base, you would see gnawing marks where the animal has chewed. If so, the installation of a small corral of chicken wire 12 inches around the base and sunk about 2-3 inches into the soil will deter this destructive creatures.

Second, examine the base of the dying branches themselves. Follow the branches back to where they extend from healthy plant tissue. Squirrels love to chew on the bark of Japanese Maples. Once again, look for gnawing marks and missing bark. If you suspect squirrels, control may be more problematic if not impossible. Trapping and removing squirrels from your landscape may help to reduce their population, but it isn't easy or really practical. You could, of course, simply attempt to call a truce by placing a non-resistant bird feeder and bird bath for water nearby that will attract the squirrels away from your tree.

A third possibility is the dreaded Asian Ambrosia Beetle. The female beetle which is active in the spring and summer will bore into the trunk or larger branches of a wide variety of trees to lay her eggs. In an interesting maneuver, she introduces a fungus to feed her developing young. It's this fungus that clogs the tree's vascular system leading to partial or complete death. Look for tiny bore holes the size of a pencil tip in trunks or branches that are usually an inch or greater in diameter. Occasionally, small "toothpicks" of sawdust will extend from the holes. This is a definite sign of AAB infestation. Once attacked, there isn't much to be done and that part (or the entire tree) is dead. Preventative sprays can be applied in the very early spring to discourage the female beetle from boring into the tree. Walter has a link for more information. For the average homeowner, you can apply products containing permethrin or bifenthrin in the early spring. Better products are available but they require someone with a commercial license to apply them.

Finally, the damage to this tree could have been caused by careless applications of chemicals, specifically weed killers. The tree in question is located and overhangs a nearby area of lawn. There are also weeds in the island near the base of the tree itself. If someone was spraying weed killer and the chemical drifted onto the foliage, that would definitely cause the damage shown. Even the careless application of liquid fertilizers can burn the foliage of plants. With chemical mishaps sometimes only the foliage is damaged. The branches with their underlying dormant buds may not have suffered permanent harm. Examine the branches to see if they are still pliable and green. If so, the tree may leaf back out next spring and the experience will be a thing of the past.

My advice to Gene is to wait until next spring to do anything. If these branches fail to put out leaves and are obviously brittle and dead, it will be time to pull out the pruners and remove them. A light dose of fertilizer at that time will also help. Until then, make sure the mulch is properly applied to a depth of 2-3 inches. That's about all you can do for now.

If you are concerned about the trees in your landscape, you can contact a Certified Arborist or a professional tree company in your area through the web site of the Georgia Arborist Association.

If you have comments or questions about this article or want to submit a question that may be used in a future article, please email me.

Unless otherwise noted, Images & Drawings Copyrighted © 2009 by Theresa Schrum - All rights reserved