Question
We have lived in our home for 24 years. There are 4 arborvitae trees that are a western wind break. These trees were full grown when we moved in. They are are about forty feet tall.

During spring clean up I noticed that in one of the aborvitaes that there is a hole where there once was a branch. The tree looks hollow. Very concerned about this.

What is the live span of this tree?

All four of them lean toward our house. Also have noticed Carpenter Ants in the area.

And last year was a bad drought year in this area. (Lost 2 azaleas that were 20 years old!)

I think I have already answered my question: the trees need to go.

But give me your opinion. Because I am just sitting here shaking my head at what the cost will be to take down these antique trees!

Dick and Helen

Answer
Just because a tree is hollow dose not mean it is dying. The living part of trees are the outer cells of the trunk and branches and the leaves. The only problem with hollow trees may be the fact that they could break during wind storms. But if the tree will not hit anything IF it fell it is not considered a hazard tree.

Arborvitae has many species of tree in the family. In the natural setting thujas grow very old. These trees have been crossed and bred as a smaller tree for homes and as hybrids and being grown in the yard away from it natural setting they live shorter lives. The life span can be from 50-a couple of 100 years old depending on the tree and its location.

If the foliage is still green and healthy the tree is ok. Thuja wood does not decay fast so I would think the tree is not hollow and the hole does not extend too deep. Now carpenter ants will and can nest in a tree and extent "holes" in a trees trunk.

I would treat the hole with an insecticide if the ants are in it. This will keep ants out and stop or slow the expanding of the hole.

The leaning (you said the tree were for a wind break) depending on what type and extent of the winds you have there is more than likely the result of the wind over many years.

The bottom line do you want or like the trees there and are they green and full and healthy looking--if so I would keep them. It will take some years to grow another line of trees for the wind break.

From what you said I would lean toward keeping them and maybe treating the ants.

Carpenter ants
Carpenter ant nests are very common inside trees, especially older trees that are hollow or have a significant amount of dead limbs and branches. The nests are usually in rotted, decayed wood, although some nests may extend into sound heartwood in the center of the tree.

Carpenter ants in trees are not directly harmful to the tree. Control is not essential for the tree's health, as the ants are only taking advantage of an existing situation of soft, weak wood in which to establish their colony. Stress, mechanical injury, environmental conditions, disease or other insects are responsible for killing limbs or sections of the trees in which the ants are able to nest. Once injury has occurred, wood decay can set in if moisture is present; it is the wood decay that gives the carpenter ants the opportunity to colonize the tree. Carpenter ants use knots, cracks, holes and old insect tunnels to gain access to these areas.

Dust insecticides (such as Sevin or rotenone) labeled for use on trees in the landscape are suggested for control. Apply the dust directly into the nest cavity.

Plugging or sealing tree cavities or treating tree wounds with wound dressings is not advised. Such treatments are unnecessary and will not eliminate nor prevent decay or carpenter ant activity.