Ants in Tree / Trunk Damage

Kenosha News – July 7, 2016

Barb Larson, Horticulture Educator

Question: My problem is with ants in a maple tree in my yard. The trunk has a split and a “hole” and ants, I think carpenter ants, big black ones, are all over the tree. My wife is certain the ants will kill the tree and it makes sense to me that they probably will. Any thoughts? R.B.

Answer: I agree your maple tree has a carpenter ant colony, which isn’t unusual for larger trees. Inside the tree is an area of soft, damp or decaying wood, which is a perfect spot for carpenter ants to build their home. Ants won’t kill the tree. The rotten wood or whatever caused the decay may cause tree dieback or death. My major concern is large areas of decay can weaken the structure of the tree’s trunk and limbs. If the trunk or a large branch breaks will it fall on the house or cause some other harm?  I suggest hiring a certified arborist to evaluate the tree for structure and safety. Do an internet search for Wisconsin Arborist Association, then go to the “Arborists for Hire” section to find certified arborists working in Kenosha County. An arborist can prune the tree for better structure and stability.

Carpenter ants in tree should be left alone because the colony will remain in the tree and will be less likely to make a nest in your house wherever there is wet wood (e.g. leaky eves, behind bathroom tile). It is normal to have a few ants wander into the house looking for food. If large numbers of ants are found indoors, then the colony in the house should be uncovered and treated, and the tree colony might be treated as well. University of Minnesota Extension and Iowa State Extension have good factsheets on carpenter ants in trees if you need more information.

Question: I have a 10 year old maple tree in my yard. About a third of the branches seem to be dying or dead. I noticed a fairly large area on the trunk when the bark is loose and starting to fall off. Can anything be done? A.N.

Answer: The vascular system and growing area (cambium) for a tree is directly under the bark. Any damage and loss of bark will cause loss of sap flow to the upper part of the tree. Because the sap runs straight up the tree from roots to canopy the biggest impact on tree health is the bark missing around the circumference of the trunk. Many trees tolerate trunk damage and heal over time.  But additional stressors, like drought, can push the tree from coping to dying. A tree that was already compromised will suffer even greater impacts on its health and growth.

What can you do? Support the health of the tree. Water every 10 to 14 days if we don’t get 1 inch of rainfall. Irrigate under the tree’s canopy so it gets wet 6 to 8 inches deep in the soil. Prune out any dead branches. Established trees don’t require fertilization if you regularly fertilize the lawn around the tree.