2018-01-31 / Gardening Tips

Hazard Tree Diagnosis Part 2

By Bob Beyfuss

Last week I wrote about the difficulties in determining whether or not a tree presents a hazard to people or property. This week I will tell you how to recognize a few “red flags” that should allow you to get a better idea if there is a problem. I received several emails from people who had tree disasters that they did not see coming at all.

Since plants lack speech to tell you if they have health problems, diagnosing their health requires you to understand a bit about tree physiology and perhaps even a little about physics. Most people realize that a dead branch, or even a branch with very few healthy leaves is a sign that something is not right.

When seemingly healthy branches break off and fall, the tree owner usually sees that there was significant internal decay in the center of those branches and that decay usually has spread upward and downward from the trunk. Trees cannot heal wounds or cure internal fungal infections that cause rot. They respond to these problems by walling off tissue that surrounds the wound or internal decay.

Growing a new trunk

Trees will literally try to grow a new trunk around the decayed or dead tissue. This results in a bulge that is not obvious to an untrained eye. Any unusual swelling of a trunk or branch usually indicates internal decay. This may be easily confirmed by using a long length, but small diameter, drill bit to drill into the suspect area. A variable speed drill that allows a slow penetration makes this a bit easier. If the drill sawdust is a uniform white all the way through the branch or trunk, there is no decay in that particular spot. If the sawdust is brown or black and moist, there is decay present. If the drill suddenly hits a hollow spot, that will also be obvious.

Of course it is not a great idea to drill lots of holes in your tree, looking for decay, but healthy trees can quickly seal off these small diameter holes with little damage. Columns of decay in trees spread vertically much more so than laterally. The decay follows the top and bottoms of xylem vessels (water conducting tubes) which act much like long, skinny, straws that are perforated at top and bottom. The side walls of xylem cells are much more resistant to decay and tend to keep the infection from spreading laterally. A good place to look for internal decay is directly above and below where a branch has broken off, or where there is an obvious scar on the tree trunk. Look for a bulge and start drilling!

Other signs of decay

Other signs of internal decay are fungal fruiting bodies (woody mushrooms) growing out of the trunk or at the very base of the tree. These “bracket” fungi always indicate internal decay and are therefore “red flags”. If the tree has plants growing out of a crotch where two or more branches arise, this too indicates decay and is another red flag.

Narrow crotch angles, such as you would see if you use your index and middle finger to make a “V” sign (or a “peace” sign to aging hippies) present a long term problem. As each of the “fingers” grows wider over the years, it pushes on the other and may cause that crotch to split open, especially if either or both branches has some internal decay. Structurally, a crotch angle that resemble the angle formed by extending your thumb and middle finger as wide as possible, will allow each of the branches to grow thicker without pushing on the other branch.

The worst type of failure is when an entire tree falls over and crushes something important, like your house, car or your garage. Although this may appear to happen spontaneously, there are usually clues before it happens. If you notice that your entire tree appears to be “listing” or leaning to one side or another, even slightly, carefully examine the ground on the opposite side of the “list”. If the ground appears raised up, even just a few inches, this is a serious red flag, as it indicates that the roots are on that side are rotted and can no longer support the weight of the leaning tree.

Next week I will discuss some ways to address these issues.

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