We've several trees of different varieties that have holes in the bark. They are spaced evenly, a little less than 1/4" apart and are in rows/columns. One tree, a mountain ash, has died and I've noticed these same holes now appearing on our clump of birch trees. What causes this and what should be done to protect more trees from dying?
Minnesota Master Gardeners say:
The holes you have described sound like the work of sapsuckers. These birds drill holes so they can feed on sap that accumulates in them. They may also feed on insects attracted to the sap. The holes, though often numerous, are superficial and usually do not seriously damage trees. However, the wounds can provide points of entry for insects or disease and when sapsuckers are particularly persistent a tree may decline or die as a result of the birds' activity. Mountain ash and birch are among the species most attractive to sapsuckers.
In central Minnesota, sapsucker damage is usually most evident during the birds' spring and fall migration. When you see the birds at work or observe freshly dug holes you may be able to discourage them by covering the affected areas with heavy paper, hardware cloth or tree tanglefoot or you could try tying boards or strips of wood to the affected trunks or branches. Scare tactics can also be effective in the long run, but that requires persistence.
Here are some links to more information about sapsuckers and how to control them.
