MANAGING GIANT POLYPORE ON BEECH TREES

What is Meripilus giganteus?

Meripilus giganteus, also known as the giant polypore, is a fungal pathogen that primarily affects beech trees. It causes root and lower stem/basal rot, weakening the tree’s structural integrity and increasing the risk of failure.

Identification Guide

Meripilus giganteus fruiting bodies:

• Annual & Soft: Develops quickly into a frond-like mass.
• Early Stage: Starts as a yellow-white mass.
• Mature Stage: Tan to dark brown upper surface; off-white pore layer beneath.
• Distinctive Feature: Fronds bruise black when touched.
• Spores: White; flesh is off-white.
• Senescence: Hardens and turns charcoal black, sometimes with red-brown banding.
• Wet Conditions: Fruiting bodies often disintegrate.

Signs of Infection (host tree)

Watch for:

• Evidence of the fungal fruiting bodies around the base of the tree or surrounding ground.
• Folia dieback, thinning of crown or reduced leaf/bud density.
• Mushy or decaying roots near the base.

Why is it a concern?

• Safety Risk: Meripilus giganteus favours roots making identification of decay difficult. Infected trees can collapse without warning, posing a significant hazard to people and property.
• No Cure: Once infection is established, there is no effective treatment, only appropriate management of the host tree. Unfortunately this commonly results in removal and/or harsh crown reduction.

Preventative Measures

To reduce the risk of infection:

• Avoid Wounding: Prevent injuries to roots from pruning, proximity of construction work, compaction of soil, or damage by landscape machinery.
• Sanitize Tools: Clean pruning tools to avoid spreading fungal spores.
• Improve Tree Health: Provide adequate moisture and nutrients to keep trees vigorous.
• Proper Spacing: Avoid planting trees too close together to reduce root contact.
• Maintain Soil & Mulch: Use soil treatments at planting and maintain good aeration and mulching around the base.

Management of Infected Trees

• Professional assessment: A qualified and experienced arboriculturist should evaluate structural stability. The arboriculturist will assess the extent of colonisation and decay and prescribe suitable remedial tree works and/or on-going monitoring schedule to appropriately manage the host tree. This is also dependant on the trees location and the severity/value of target zones surrounding the tree.
• Remedial tree works: Ultimately, total removal is likely to be the outcome of a Beech colonised by Meripilus giganteus. However, in cases of early identification an arboriculturist may be able to prescribe a programme of root feeding to improve the trees vigour and reduce the rate of decay or a phased crown reduction to mitigate a reduction of structural integrity allowing the tree to remain in the short term.
• Dispose of infected material: Remove and burn or properly dispose of roots and stumps to prevent spore spread.
• Ongoing Monitoring: Regular inspections for signs of fungal activity.

Get in contact with our arboricultural team if you require assistance with Tree Surveys