Root and Butt Rot caused by Kretzschmaria deusta
The fungal pathogen Kretzschmaria deusta is sometimes known as the burnt crust fungus or brittle cinder fungus.
Root and butt rot from Kretzschmaria is most common on European beech (Fagus sylvatica) in landscape settings in the region. The fungus can also be found on American beech (F. grandifolia), sugar maple (Acer saccharum), red maple (A. rubrum) and Norway maple (A. platanoides). Less common hosts include oak (Quercus) and linden (Tilia), among other hardwoods.
Symptoms & Disease Cycle
Kretzschmaria is a destructive white rot pathogen of hardwoods, decaying both lignin and cellulose. However, unlike many white rot fungi, cellulose is preferentially targeted and in some ways, Kretzschmaria is more like a brown rot fungus. As cellulose is decayed, infected wood rapidly loses strength. But interestingly, the wood still appears relatively sound, due to the pattern of decay this fungus exhibits. Infections can initiate in the roots and spread to the base, where the fungus causes a butt rot of the lower trunk. Additionally, Kretzschmaria can colonize basal wounds, which are far too common on landscape beech trees. Decaying wood appears bleached with distinct black zone lines intermixed in the decaying wood. Like most wood-rotting fungi, symptoms are often cryptic to non-existent. Undersized foliage, canopy dieback, basal cankers, sap flow and sloughing bark can develop as infections intensify. Bleeding cankers can also develop and may be confused with those caused by Phytophthora.
Signs of the pathogen include gray-colored fruiting bodies with bright white margins that are produced from late spring to early summer. These structures appear mostly flattened from a distance and are very different from the fruiting bodies of most wood-rotting pathogens. Upon closer inspection, the fruiting bodies appear as lumpy masses growing from infected bark. Over time, the fruiting bodies become dark black in color and may be difficult to distinguish from dead bark scales soaked with sap. The fruiting bodies are almost always produced very close to the soil line but may be higher on the trunk when advanced infections exist.
Kretzschmaria produces airborne spores from fruiting bodies that can establish on surrounding beech or maple with basal cankers. Spread also likely occurs through root grafts between susceptible trees. However, overland spread is believed to be limited as multiple infected trees in a "disease pocket" are uncommon in landscape and forest settings. Nothing can be done to eradicate the pathogen once present since the fungus lives in roots and the heartwood. Boosting vigor and minimizing additional stresses are really the only management strategies for advanced wood rot infections. A basal bark application of phosphites may help to slow the progression of the disease into the sapwood and cambium but ultimately the tree will die as a result of the disease. Upon death, try to remove as much of the root material as possible. If the stump is left, the fungus will persist on site and may infect a newly planted tree nearby. Avoid replanting with beech or maple when the tree is removed.