Regional Gardening Reports :: National Gardening Association

In the Garden:
Northern & Central Midwest
December, 2009
Regional Report

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These lichens on the bark of a shagbark hickory are beautiful and harmless.

Issues With Trees

Now that most of the leaves are down on the deciduous trees, it's a good time to take stock of exactly what is going on with the trees. The weather is still pleasant enough to go out and do some scouting for problems. Here are some of the issues you may come across:

Bronze Birch Borer
We've all seen the white birch with two or three stubs where part of a branch has been cut out. This type of "flagging" in a white birch, which means that a branch has died, is usually an indicator of bronze birch borer damage. The borer lays its eggs under the bark, and when the larvae hatch, they tunnel around in the layer just under the bark that contains the transport tissue. If the borer makes a tunnel all the way around, the branch dies. Other indicators include bumpy lines on the bark which actually follow the borer trails, and D-shaped holes which is where the borer emerges.

Emerald Ash Borer
Emerald ash borer produces similar signs and symptoms to the bronze birch borer except that the dieback starts in the upper third of the canopy and then progresses downward until the tree is bare. Other signs include splitting bark and D-shaped exit holes. If you peel the bark off either of these trees (after they are dead, of course), you will see the galleries dug by the larvae.

Increased sapsucker damage on any tree, shown by rows of holes drilled into the bark , is an indicator of some type of insect under the bark. Most trees can withstand the actual damage by the sapsuckers, but the tree may succumb to the damage being done by the insects under the bark.

Fungal Wilt
Single or multiple branches dying on Norway maples or redbuds are usually indicators of a fungal wilt that the tree has internally (there are other trees that are susceptible). The fungus effectively plugs up the transport tissue and cuts off the water supply. Unfortunately, if your tree does have this fungal wilt, you have to be careful in choosing a replacement because the fungus resides in the soil and will infect other trees that are susceptible.

Localized dead areas on tree trunks, which may or may not be oozing, usually indicate canker. In many cases the tree will heal itself, but if the canker becomes too advanced, the tree may succumb or break. Cankers can be caused by mechanical damage, environmental conditions, or fungi and bacteria. Cankers may appear sunken on young trees. The best treatment is prevention. Since cankers tend to invade stressed trees, keeping them as healthy as possible will help avoid problems.

One last issue you may come across is rough gray-green patches on tree bark. These are lichens, specialized organisms which are combinations of an algae and a fungus. Best of all, they are completely harmless!

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