Question
We had a very bad thunderstorm last night and one of my green ash trees broke in half. The tree looked perfectly healthy on the outside, but I found the condition inside the tree to be light brown in color, came apart easily and it felt more like balsa wood.  I saw some bore holes in the interior, but was not able to recover any type insect or larva. Can you tell me what would cause this tree to have these conditions, especially the balsa wood type finding? Part of the inside was also spongy and like sawdust.

Thank you.  

Answer
Sounds like one of the heart rot decay fungi. Several wood-rotting fungi attack living green ash trees. The most common is Fomes fraxinophilus. Two other fungi, Polyporus sulfureus and Phellinus punctatus, also cause heart rots in living ash trees in North Dakota. Heart rots are much more severe in mature and overmature trees in native woodlands.

Symptoms The rotted area as seen in cross section of the trunk is very irregular in outline and often is more extensive on one side of the tree The normal wood of the white ash is light yellow In the first stages of decay the wood is stained brownish Later the affected wood becomes whitish and is surrounded by a brown zone where the decay is extending into the normal wood The spring wood of each annual ring becomes white while for a time the summer wood remains brownish Shortly however the summer wood becomes whitish and in the final stages of the decay the wood is soft and crumbly.