Heart Rot Tree Disease - Prevention and Control

A Common Disease in Tree Heartwood

Heart Rot Conk Mushroom. USDA Forest Service, Northern and Intermountain Region , USDA Forest Service, Bugwood.org

Heart rot in living trees is caused by many fungal agents and pathogens which have entered the tree through open wounds and exposed inner bark wood and infected the "heartwood". Heartwood makes up most of a tree's inner wood and support so rot here will cause tree failure over time. Heartwood cells have some resistance to decay but depend on a barrier of protection from the bark and outside living tissue.

It can occur in both hardwood and deciduous tree species but is especially common in Oaks via I. dryophilus and P. everhartii  decay fungi.

More on Heartwood

It should be noted that heartwood is genetically programmed to spontaneously and annually separate from living wood tissues. Once heartwood formation is annually laying down layers and growing in volume, the heartwood quickly becomes the largest part of the mass of all trees. When that living barrier of protection fails, diseased heartwood softens resulting in trees being structurally weaker and prone to breakage.

Usually, a "conk" or mushrooming fruiting body is the first sign at the site of infection. All deciduous trees can get heart rot while resinous conifers have some extra resistance. A useful rule of thumb suggests that a cubic foot of wood has decayed for each conk produced - there is a lot of bad wood behind that mushroom. Fortunately, heart rot fungi do not invade living wood of healthy trees.

Heart rot is a major factor influencing the economics of logging high-value lumber and becomes the natural growth dynamic of many older forests. Heart rot is prevalent throughout the world affecting all hardwood trees and can be very difficult to prevent. 

Prevention and Control of Heart Rot

As long as a tree is growing vigorously, rot will be confined to a small central core.

This is called tree wood compartmentalization. If the tree is weakened and fresh wood exposed by severe pruning or storm damage, decay fungi can advance into more and more heartwood.

There is no economically feasible fungicide to use on a heart rot hosting tree. The  best way to prevent heart rot in your hardwood or conifer tree is to keep your tree healthy using proper management techniques: Take this test.

Minimize pruning wounds that expose large areas of wood. Shape trees at an early age so major branch removal will not be necessary later. Remove broken branch stubs following storm damage. Have suspect heart rot trees checked by an arborist to determine if sufficient live wood is present for structural safety. Check trees every few years to be certain new growth is maintaining a sound structure. Large trunks and main branches with extensive decay may have little sound wood to support the tree.