Japanese Maple

(Question)

An established cut leaf weeping Japanese Maple did not survive last winter, however 10 others on the same property did. It simply did not bud or come into leaf at all. The location was sun am shade pm. Garden has clay soil. Tree was transplanted 7 years ago, actual tree was about 15 years old.
Attached is a photo of the tree plus its roots. There is a white powdery type growth on the closest to the surface roots. Anybody know if this had anything to do with its death? Any ideas on why it died? It did show signs of leaf burn last summer and it was well watered going into winter and had a good covering of Cedar mulch over its roots.

(Answer)

This past winter was very hard on even well-established trees and shrubs, and many Torontonians have reported the inexplicable and sudden death of a previously healthy tree.  It is quite possible that even the small amount of stress from the previous summer rendered your Japanese Maple unable to make it through the harsh conditions. 

There are no diseases of Japanese Maples that describe a powdery substance on the roots as a sign or symptom, so it is most likely that the white powdery material you see on your Japanese Maple roots is a the vegetative part of a fungus, known as mycelium, which plays a vital role in breaking down plant material in the soil, and is an important source of nourishment for soil invertebrates. You may have come across other instances of mycelium on wood that has been buried underground, on rotting straw or on leaf mould.  It is not harmful – on the contrary, mycelium plays a vital role in the breakdown of organic materials – and it is not the cause of your Japanese Maple’s demise. 

A possibility may be Armillaria root rot disease, which is a widespread forest disease in Ontario, although some sources say that Japanese Maples are resistant.  To determine whether this may be the cause, you could look for the signs: a soggy, whitish layer of fungal threads or “shoestrings” (the mycelial mat) between the surface of the inner bark and the outer sapwood of the tree.  Pale honey-coloured mushrooms around the base of trees or in adjacent soil are another indicator of this disease.  The Ontario government’s website gives a good description:  https://www.ontario.ca/environment-and-energy/armillaria-root-rot.

Here is a link to the Toronto Master Gardeners fact sheet on Japanese Maples which provides a brief description of the diseases that can affect these trees: https://www.torontomastergardeners.ca/index.php/factsheet/growing-japanese-maples-a-toronto-master-gardeners-guide/

And here is another very interesting read about the effects of a long cold winter on trees and shrubs: https://ag.purdue.edu/hla/Extension/nle/Articles/TheRevealingEffectsofWinteronTresandShurbs.pdf