Thursday, January 8, 2015

Your Lovely Tree is Dying from the Inside Out

Kimberly Labno

I consult with urban dwellers on their horticultural needs. Recently, I met a client with two gorgeous mature white oaks flanking the entrance of his Center City residence. One of the trees had a fungal growth at the base, about 12 inches in breadth and maybe 1.5 inches in height, and it had been routinely removed for appearance sake by the owner's house staff. The tree had an overall strong canopy. Even though the wound was shallow and there was little wood rot in the trunk, I knew the tree was dying.
                                                               (courtesy of RHS)
The tree fungus is Ganoderma sp., commonly known as shelf or bracket fungi. The fungus causes what is called butt rot and root rot. It has significant impact on oaks, and potentially especially those near the end of their life expectancy of 65-85 years old - note this expectancy is based on trees in naturalized settings, not urban tree pits. The visible fungus is a fruiting body, which means that the fungus is systemic.

If it helps, you can visualize a flowering shrub with infected roots and flowers in bloom- the fungus has established in the base and/or roots of the tree and the visible fungus is the flower in bloom. There is no cure and removing the fruiting body has little to no impact on control of spread, outside of reducing the number of spores released that may enhance disease spread from say tens of millions to just millions in number. The plant is dying from the roots outward. Eventually, the tree will show signs of sickness like leaf dieback and discoloration. Based on the literature, the lifespan of a tree with this fungus is something on average like between several and ~ 10 years. In natural settings, most trees with this rot meet their end from breakage or toppling in winds/storms.

The client was a sad about losing the trees and although the tree was leafing out well and he could play a waiting game for the infected tree to die- and infect the neighboring oak, he choose to seek removal estimates from professional arborists. The arborist concurred with my diagnosis and outlook and recommended replacement trees that are probably familiar to many as reliable street trees.

To learn more, here are a handful of references.

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