Question
I have a problem with a very large pecan tree. apparently a limb had been cut by a previous owner and we noticed "holes" that were multiplying in that area. We covered the area with tar. The holes have "re-appeared" and now there is a mushroom growing out of one of them.  I hate to cut the tree down. It is so beautiful. Is there hope to save it? I was thinking of "cementing" the hole. What do you think?

Answer
The mushroom is the fruiting body of a decay fungi that has entered the wound where the branch was cut. Decay fungi will grow in the woody part of the enter trunk. These are dead cells and their being decayed will not cause any problem with the health of the tree. The decay fungi will not infect the living cells which are just under the bark. If the tree looks healthy and the foliage is full and green there  is no reason  to cut the tree. The worst thing that could happen would be the tree would lose strength in the trunk. The tree will become hollow over time. IF large limbs start to break off during high wind storms that also show signs of being hollow then you might start to become concerned about the hazard of the tree breaking off and falling on something.BUT this will or could be many many years from now.

Filling of hollow trees, a process called "cavity filling," was practiced by arborists for many years. Thanks to modern research, it has been discovered that cavity filling is not needed to support or improve the health of hollow trees. Tree experts have found that cavity filling with cement can actually damage a hollow tree. The column of cement created in the tree by a cavity fill doesn抰 move, just like a column on a building, but the tree is always moving. It sways with the wind constantly. The rubbing created by the swaying tree and the solid column of cement further damages the tree.

Decay organisms, such as rot fungi, that created the hollow in the first place are able to take advantage of the new injuries created by the rubbing and invade the healthy tissue of the tree. If that wasn抰 bad enough, the cement holds moisture, creating a favorable environment in the filled cavity for the decay organisms! Tree experts explain that it is much the same as when carpenters place a vapor barrier between a house抯 foundation and the wooden sills. If they put the sills directly on the concrete foundation, the wood will rot rapidly. If you place cement in a tree cavity, it will speed the wood decay! If cavity filling is desired for aesthetic reasons, there are some new synthetic foams that can be sprayed into the cavity by professional arborists. These materials will bend with the swaying tree. There is really no reason to fill a cavity; it doesn抰 improve the tree抯 health and doesn抰 offer any added support.


Instead I would fertilize the tree once a year with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. This will help the overall health of the tree.