What Is Heart Rot Disease: Info About Bacterial Heart Rot In Trees

What Is Heart Rot Disease: Info About Bacterial Heart Rot In Trees

By: Teo Spengler

Heart rot refers to a type of fungus that attacks mature trees and causes rot in the center of tree trunks and branches. The fungus damages, then destroys, a tree’s structural components and, in time, makes it a safety hazard. The damage can initially be invisible from the outside of the tree, but you can detect diseased trees by the fruiting bodies on the outside of the bark.

What is Heart Rot Disease?

All hardwood trees are susceptible to varieties of fungal infections known as heart rot tree disease. The fungi, especially Polyporus and Fomes spp., cause the “heartwood” at the center of these trees’ trunks or branches to decay.

What Causes Heart Rot?

The fungi causing heart rot in trees can attack almost any tree, but old, weak and stressed trees are most susceptible. The fungi destroys the tree’s cellulose and hemicellulose and sometimes its lignin, making the tree more likely to fall.

At first, you may not be able to tell if a tree has heart rot tree disease, since all of the decay is on the inside. However, if you can see inside the trunk because of a cut or injury to the bark, you may notice a rotted area.

Some types of heart rot in trees cause fruiting bodies that look like mushrooms to form on the outside of trees. These structures are termed conks or brackets. Look for them around a wound in the tree bark or around the root crown. Some are annual and only appear with the first rains; others add new layers each year.

Bacterial Heart Rot

The fungi that cause heart rot tree disease are divided generally into three types: brown rot, white rot and soft rot.

  • Brown rot is generally the most serious and causes the decayed wood to become dry and crumble into cubes.
  • White rot is less serious, and the rotted wood feels moist and spongy.
  • Soft rot is caused by both fungus and bacteria, and causes a condition called bacterial heart rot.

Bacterial heart rot progresses very slowly and causes the least structural harm in trees. Although they do cause decay in cellulose, hemicellulose, and lignin in affected trees, the decay does not spread quickly or far.

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Ponderosa Pine Diseases

The multipurpose ponderosa pine (Pinus ponderosa), or western yellow pine, is susceptible to a number of diseases that cause severe damage unless treated immediately. While some diseases damage the roots or needles, others rot the heart or inner section of the tree and cause branches to fall. Treat the disease plaguing your ponderosa pine immediately so the tree regains its natural health and vigor.

Downed trees victims of heart rot

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In the wake of last month’s wind and rain storms, many trees throughout the San Fernando Valley have lost branches, split apart, or been uprooted altogether. I recently witnessed the remnants of three of these trees — one in Woodland Hills, one in North Hills, and one in Valley Village.

Sometimes you need nothing more than a few inches of tree stump to diagnose what happened. If the stump is hollowed out with an interior of soft, fibrous mulch-perfect material, the tree in question is probably a heart rot victim. Heart rot is a wood decay disease caused by a variety of fungi that may affect nearly all species of commonly planted urban trees and is often implicated when large limbs are broken off during a storm. Once a tree limb is hollowed out by heart rot, it loses the strength to withstand what arborists call “dynamic load,” the sort of stress created by a strong wind, and is sure to break off the trunk — often taking the trunk with it — in a significant winter storm.

From what I have seen, deciduous or hardwood trees growing in the Valley whose habitat is the Eastern United States and are more than 50 years old are especially vulnerable to heart rot. Fungi that cause heart rot enter trees through wounds that are caused either by storm damage or by improper pruning cuts. And what 50-year-old tree has not been subject to one or both of the above?

It should be noted that even dry climate trees, such as certain eucalyptus species, begin to decline in vigor at around 50-60 years of age in urban settings, including the San Fernando Valley.

How do you know if your tree has heart rot and could be susceptible to significant limb breakage in a storm? If you see fungal fruiting bodies — commonly known as mushrooms, conks or brackets — growing on the trunk or branches, you are almost certainly looking at a tree afflicted with heart rot. Yet trees can have significant heart rot and not necessarily display fungal fruiting bodies, which only appear when the fungus infection is in an advanced stage, often having been present in the tree — without any visible sign of its existence — for years.

Parkway trees, those that eke out a living on those narrow strips of ground between sidewalk and street, are the most beleaguered specimens of the urban forest. This is especially the case with riparian or riverbank trees, whose roots are most comfortable growing laterally but, in parkway strips, are hemmed in by concrete. River birch (Betula nigra) is a case in point. This species, indigenous to flood plains and riverbanks of the Eastern U.S., was planted as a street tree in certain Woodland Hills neighborhoods more than half a century ago. No wonder it has mostly disappeared from those neighborhoods, victimized by root restriction, severe periodic droughts, and heart rot. During one of last month’s storms, a 60-foot specimen split apart. Yet a relatively new river birch selection known as ‘Dura-Heat’ is now available in local nurseries. Its superior heat resistance, ability to grow in sun or shade, exfoliating and cinnamon colored bark, as well as its adaptability to most soil types, makes it a candidate for local planting, albeit in a large backyard as opposed to a parkway location.

Silver maple (Acer saccharinum) is another formerly popular street tree that has all but vanished from our urban forest. Its foliage is its main attraction, green on one side and silver on the other, and it positively glistens in a breeze. Somehow surviving for over half a century in a North Hills parkway strip, it, too, fell over in one of our December storms, a victim of heart rot.

Last but not least, a massive Deodar cedar (Cedrus deodora) was recently uprooted in Valley Village. No signs of heart rot were visible but it is likely that a sudden influx of water, taken up from the ground during December rains, created a top heavy condition that the root system, revealed to be quite shallow — perhaps because the tree was growing in a heavily watered lawn ­— was unable to support.

For more information about area plants and gardens, go to Joshua Siskin’s website at www.thesmartergardener.com.. Send questions and photos to [email protected]

Fusiform Rust


In forest stands these diseases are of minor importance on oak (alternate host). However, they affect the aesthetic value of shade trees and ornamentals. Fusiform rust on pine (primary host) is the most important disease of pine in the Southeast.


Small yellow spots develop on the leaf surfaces in spring. Some defoliation may occur. Red, water and willow oaks are primarily affected. White oaks are seldom affected.


Leaf rusts require two hosts to complete their life cycle. Fungus spores (aeciospores) produced on pine galls are windblown and infect young oak leaves. Spores (urediospores) are produced on the oak leaf which reinfect oak. Spiny-like hairs (telial columns) on the lower oak leaf surface release teliospores which produce another spore stage (basidiospore) that infects pine. This infection results in a gall with aeciospores, and the cycle is complete.


Heart rot

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Heart rot, any of several diseases of trees, root crops, and celery. Most trees are susceptible to heart-rotting fungi that produce a discoloured, lightweight, soft, spongy, stringy, crumbly, or powdery heart decay. Conks or mushrooms often appear at wounds or the trunk base. Heart rot in trees does not usually affect the living sapwood but does cause structural weaknesses and can lead to broken branches and trunks. The disease causes economic losses in the lumber industry, since infected trees are often unsuitable for timber. Trees wounded by logging machinery or by felled trees are more susceptible to heart rot fungi.

Other types of heart rot are caused by nutrient deficiencies rather than by fungi. A dark brown to black internal rot of beets, carrots, rutabagas, and turnips is caused by a deficiency of boron. A similar rot of celery, fennel, and parsley is induced by calcium deficiency. Both of these types of heart rot can cause crop losses in poor soils. See also rot.

This article was most recently revised and updated by Melissa Petruzzello, Assistant Editor.

Shoestring Root Rot

Shoestring root rot, formally known as armillaria root rot, is a soil-borne fungal disease. The maple family is commonly infected by this disease. The shoestring fungal spores prey on weakened maple trees that have been stressed by severe weather conditions, such as excessive heat and drought, poor drainage and wet feet, frost, and lack of sunlight. The disease infects the maple tree through its root-weakened root system and kills the tree’s feeder roots. Infected maple trees experience yellowing and discoloration of their foliage, loss of vigor, dieback and premature defoliation. Smaller maple trees will succumb to the disease much quicker than larger maple trees. Shoestring root rot can be prevented by maintaining the maple tree’s vigorous growth and keeping its area free of defoliated and decayed debris. Chemical treatments are not recommended for infected trees, as explained by the University of Illinois Integrated Pest Management.

  • Shoestring root rot, formally known as armillaria root rot, is a soil-borne fungal disease.
  • Shoestring root rot can be prevented by maintaining the maple tree’s vigorous growth and keeping its area free of defoliated and decayed debris.

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