Beware of false charcoal (Ustulina deusta)

One of scariest fungus diseases is Ustulina deusta (ust-you-liner doy-ster). It rots the wood without there being any external, compensatory growth by the tree, the fruitbody is small, black or grey and not easily spotted and, to cap it all, it was renamed a few years ago and its new name is even harder to say!  Try getting your jaw round Kretzschmaria deusta.

Ustulina deusta fruitbody on beech

Clear reaction zones in lime stump

This disease weakens the wood of the tree, principally near the base, and leaves it very brittle and liable to fracture.  I’ve known trees to collapse with little wind and no warning.  Once felled you can see that the affected wood has become very hard and inflexible, the fracture plane of wood is described in the books as being like a ceramic surface.  In the wood of the broken tree you can see many sharp, dark lines zigzagging across its cross section.  These show where different fungus individuals have bumped into each other and formed a boundary.

The perennial fruitbody is dark grey to black and grows like a scab on the bark or exposed wood.  The scab is knobbly and it looks a bit like charcoal.  But it doesn’t smear your fingers with carbon when you crush it.  If the infection is at an advanced stage there may be quite an area around the base of a tree covered in the fruitbodies.

I’ve often seen Ustulina growing on beech alongside Ganoderma brackets, the two fungi working in concert to strip the wood of any nutrients they need.

In Spring the new fungus growth appears grey rather than black.  This is an asexual stage of growth.

Asexual growth growing on normal growth in early spring

Ustulina attacks many broadleaved species but I’ve seen it mostly on limes and beech.  Wherever it is found it is a potential hazard and, if there are people or property close by the tree should be checked out thoroughly as quickly as possible.