Mulberry Heart Rot: Managing Structural Decay in Mature Trees

Diagnosing the 15–20 ft Mulberry with Trunk Decay

Your mulberry (Morus spp.) losing bark at the base (9–12" on south side), exposing interior wood, with normal canopy = heart rot/wood decay—fungal decomposition of non-living central wood. Common pathogens: Ganoderma, Phellinus, Laetiporus, Schizophyllum.

Key Understanding

• Heart rot fungi only colonize dead wood (heartwood)
• They enter through wounds (storm, pruning, sunscald, old injuries)
• Living sapwood/phloem/cambium remains functional → canopy looks healthy
• No chemical cure exists—fungi are inside structural wood

Structural Risk Assessment

South-side decay = prevailing wind exposure. If >30% circumference or >1/3 radius decayed, failure risk increases. Conks (fruiting bodies) at base = advanced decay.

Management Options

1. Monitor: Annual canopy density check. Thinning = declining vascular function.
2. Fertilize/water: Reduce stress → maintain sapwood defense.
3. Prune deadwood: Remove hazard limbs. Sterilize tools.
4. Resist filling cavities: Traps moisture, accelerates decay.
5. Consult ISA Certified Arborist for resistograph/sonic tomography if high-value target.

When to Remove

If: canopy thins significantly, large dead limbs, conks abundant, lean develops, or targets (house, play area) at risk. Mulberries are fast-growing—replacement reaches shade size in 5–7 years.

Prevention for Other Trees

Protect trunks from mowers/string trimmers. Proper pruning cuts (no stubs, no flush cuts). Mulch rings eliminate mechanical damage.