University of Maryland Extension

Wood Rots and Decay - Trees and Shrubs

fungal fruiting body on stem

Back to Common Problems - Trees and Shrubs

Various fungi such as Phellinus spp., Trametes, Perenniporia, Stereum, Oxyporus, Climacodon, Hericium, and Polyporus may cause stem, trunk and branch rots. These fungi cause the heartwood of the tree or shrub to decay. The outward symptoms of stem rots are basidiocarps emerging from the main stem or branches. Basidiocarps are the fruiting body of the decay-causing fungi. They can be fleshy mushroom-like structures that appear annually, or hard, flattened, shelf-like, triangular or shell shaped perennial structures that grow a new layer each year as the rot progresses. Colors range from white, yellow or orange to brown or pale gray. Laetiporus sulphureus produces sulfur yellow to bright orange basidiocarps on ash, beech, cherry, maple, oak, and tulip tree.

Wood rots cause wood to decay in a number of chemical and physical reactions. Infection usually occurs when the fungus gains entry through pruning wounds, frost cracks, or broken branches. Wood rot fungi can infect healthy or dead branches. As the wood decays, the wood lignin dissolves and cellulose predominates. Lignin is the major chemical component of wood and gives wood its strength. The end result is brittle, stringy or crumbly heartwood, which is weak and may fracture across the grain, or into cubical chunks, depending on the type of wood rot.

mushrooms on ground
 

Trees: Basidiocarps of trunk and limb rots are found anywhere on the trunk or large branches. Basidiocarps located on the trunk near ground level may be the symptom of root rot or trunk rot. To determine whether it is a trunk or root rot look for other symptoms. Because the heartwood of a tree is not involved in translocation or storage of sap, there may be no other exterior symptoms of trunk rots. Root rots often cause dieback and other symptoms because they disrupt translocation of sap.

When basidiocarps are noticed, consult a certified arborist to determine the extent of the rot. Although there are no chemical cures for trunk and limb rots, they can be prevented by proper maintenance practices. To prevent infection, prune during the dormant period, as these fungi produce infection-causing spores that are released throughout the growing season, especially in fall.

Armillaria at base of tree

Armillaria spp. produces yellow
basidiocarps on ash, beech, cherry,
maple, oak, and tulip tree

large mushrooms from base of tree

Trunk rot


Shrubs: Many fungi can be found on dead and dying shrubs. There are no cures once the shrub is infected and the fungi cannot be eliminated from the surrounding soil once the shrub is removed. Although there are no chemical cures for these diseases they can be prevented by proper planting and maintenance practices. Avoid damage from improper pruning, lawn mowers, and excavation within the root zone. Avoid planting shrubs in poorly drained compacted soils or in low areas where water collects. Also, avoid placing shrubs near downspouts. Construction of raised beds or grade changes may be needed to ensure proper drainage. Root diseases on older established plants can result from changes in water drainage patterns.
Although there are no chemical cures for stem and branch rots, they can be prevented by proper maintenance practices. To prevent infection, prune during the dormant period, as these fungi produce infection-causing spores that are released throughout the growing season, especially in fall.

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