Brittle cinder fungus (Kretzschmaria deusta): what the sources record

This page describes what three published sources say about one wood decay fungus. It does not identify a fungus from a photo and says nothing about any single tree. The sources come from the United States and Italy; none is a regulator's notice. The parent page, wood decay fungi on trees, compares the fungi that have pages here.

Name and type of rot

The Missouri Botanical Garden calls brittle cinder fungus a soft rot fungus in the group Xylariaceae. It says the common name comes from the burnt or scorched look of the fungus in its sexual stage. A TCI Magazine article by a plant pathologist gives the older names Ustulina vulgaris and Hypoxylon deustum.

The garden's page says the fungus attacks both cellulose and lignin but mostly breaks down cellulose, so the wood loses strength and turns brittle. An Italian study in the journal iForest describes the same thing at cell level: the fungus makes holes in the secondary cell walls, which lowers the tensile strength of the wood. The authors say the wood becomes brittle and snaps with a characteristic fracture, and that dark lines in decayed wood are considered typical of this fungus.

Hosts

The Missouri Botanical Garden names beech, maple, linden and hackberry as common hosts. It adds oak, hornbeam, elm, tulip tree, black gum, ash and other hardwoods. The TCI author says she has found it on honeylocust, oak, shagbark hickory, beech and maple. The Italian study looked at veteran beech trees (Fagus sylvatica) in Trentino.

Where it shows on the tree

The garden describes irregular patches along the lower trunk, often close to the soil line, sometimes reaching several feet up along a crack or groove. The TCI author says that in nearly every case she has seen, it sat right on the buttress where the trunk meets the soil. She describes a flat, two-dimensional crust that can hide under snow and ground cover.

Through the year, the garden says the early stage in spring and early summer is light grey with a whitish border and may give off clear to amber droplets. For the rest of the year it is a bumpy, blackened crust that sounds crisp when broken. The TCI author gives April to June for the grey stage and July to August for the black, warty stage. The garden says the crust can be mistaken for Hypoxylon or Biscogniauxia canker, and the TCI author says it can be mistaken for slime flux or wounds.

What the sources say it can indicate

Garden: the extent of internal decay is hard to judge from the presence of the fungus alone. A tree can have a full crown and look healthy yet have advanced internal decay. The page links the decay to breakage and sudden tree failure.
TCI article: the author writes that the fungus "can be an indication of risk", that above-ground symptoms are often absent, and that a tree struck with a sounding hammer typically does not give a hollow sound.
Italian study: in a survey of 115 veteran beech trees in 40 sites, the fungus was recorded on 50.4 per cent of the trees and near the trees at 29 sites. It was present on every one of the trees that had fallen most lately before the survey. Four of the surveyed trees collapsed in the years before the paper. The authors write that the fungus, long treated as a facultative parasite, may play a larger role in the decline of old beech trees.

How it spreads and what the garden lists for management

The garden says airborne spores infect trees through wounds at the base, such as those from string trimmers or mowers, and that there is some evidence of spread through root grafts. It says there is no effective control or treatment once a tree is infected, and its list of strategies is to send a sample to a diagnostic lab, contact a Certified Arborist, and avoid damage to bark and buttress roots. For who may apply pesticides to trees at all, see pesticide licences by country.

The garden says identification should be done by an expert. For who carries out tree risk assessments, see tree risk assessment methods and consulting arborist credentials.