Most of the fungi that attack maple roots also attack roots of other trees, and their cosmopolitan nature makes direct control virtually impossible. Nonetheless, it is wise to identify those trees affected by root pathogens so that resistant replacements can be sought for future plantings.

1) Armillaria root rot, shoestring root rot
Armillaria mellea all species

A. mellea is a fungus that parasitizes roots and root collars of many different species of trees, including maples. Usually, the fungus attacks only hardwood trees affected first by other adverse environmental factors such as defoliation and/or drought. Thus, A. mellea is one part of a larger problem often referred to as "dieback-decline. "

If A. mellea is part of a dieback disorder, several observations help to diagnose its presence:

• A dense white mat of fungal tissue is visible when bark from an infected root or the root collar is removed (figure on left). This tissue is bioluminescent, and fresh mats can be seen to luminesce when viewed in the dark.
• Black, shoestringlike fungal organs (rhizomorphs) form a dense network beneath bark of trees with advanced infections (figiure in center). Rhizomorphs are the primary means by which A. mellea spreads from infected to healthy trees. They can grow through the soil for up to 10 m.
• A. mellea produces clumps of light brown mushrooms near root collars of infected trees in late summer and early fall (figure on right). The mushrooms, known to naturalists as "honey mushrooms," have slightly hairy caps, white spores, and "rings" or "skirts" about their stems. The mushrooms usually deteriorate within a week after they are produced.

2) Ganoderma root rot
Ganoderma lucidum red, sug, nwy

Disease caused by G. lucidum is characterized by presence of platelike fruiting bodies with shiny, reddish-purple tops and cream-colored edges and undersides. Usually, these "conks" are produced at bases of infected trees, but occasionally they are produced on diseased roots and seemingly emerge from the soil 5 m or more from affected trees. In northern states, conks appear in late summer and usually deteriorate beyond recognition by midwinter. G. lucidum is rare on forest trees, but common on maples (and other trees) in urban environments.

3) Xylaria root rot
Xylaria mali sug

This disease occasionally affects landscape trees, but is most common in forest stands where maples are subjected to repeated wounding of roots. Sugar maple roots in stands where trees are tapped for sap are most likely to be affected because early spring traffic in wet soils is likely to result in root wounds. Symptoms in the crown are like those of other root diseases, leaves are off-color and small, and some branch dieback is evident. X. mali produces its spores in tan (when young) to black club-shaped fungal structures that are 2-6 cm tall and 3-10 mm in diameter. These structures are produced in mid-summer but are tough enough to remain identifiable virtually all year.

4) Hypoxylon root rot
Hypoxylon deustum (Ustulina vulgaris) sug, red

H. deustum forms a black, crustose covering over dead root buttresses and stumps of many hardwoods including red and sugar maples, paper birch, white ash, and several species of oak. The fungus is a pathogen when it decays maple sprouts as they try to develop from residual stumps and root systems. As the number of sprouts killed by H. deustum is relatively small in relation to many that grow following harvesting or thinning, no control measures have been developed.