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When holly goes pathological

Only fungus and injury cause color change in normally white holly. 1998.

by Professor Gene Wengert

Recently I called a sawmill in PA about the price of KD holly. One of the selling points was that it was all white, no green. It has been rare for me to mill holly with green, however I frequently find gray spots and streaks. It is rare for me to saw any that is all white. What causes the gray, heart wood? What causes the green?

The normal color of holly is white--both sapwood and heartwood. However, bluish (or perhaps greenish?) steaks will be seen and would be classified as mineral, which is not a grading defect according to the NHLA rules.

It would be expected, however, if the tree were injured, it would close off the injured area (this is the way a tree protects itself from fungal, bacterial, and other invaders, as it doesn't have antibodies like we do). The closed off area is often called pathological heartwood (because it is like heartwood, but the heartwood is not caused by aging but by a pathogen) and the heartwood so formed is grayish in color (perhaps because of the presence of fungi that discolor the area?).

Hard maple is a species that is also well known for its ability to encapsulate the wounded area.

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.

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