Armillaria Root Rot


If you find a decaying oak or maple and see the growth of mushroom clusters, also known as honey fungus, at the base of a tree calling the experts at Advanced Tree Care, may not help save the tree involved but can save many of the trees nearby.

Armillaria Root Rot is a fast spreader, these fungi produce tough, cord-like strands called “rhizomorphs” that grow from decaying stumps and roots through the soil. It can live for years in the forest floor or where there is a wood product breakdown. This tree fungus is a root rot disease that begins in rotting oak or maple trees and spreads to other trees through the root system. It feeds off nutrients from tree roots.

The infected tree has:

  • Stunted leaves, dull-colored or wilted leaves which turn yellow or brown.
  • Die-back occurs on twigs and branches.
  • The host tree has a white rotted fungus that includes light or bleached wood.
  • Trees like spruce and yew produce a heavy flow of resin.

In the time it will kill the tree. Trees infected by armillaria root rot have decayed roots as well as decaying lower trunks.  These trees can easily apart break or fall over during a storm or during high winds.

Armillaria root rot can infect many deciduous and evergreen trees and shrubs.

The trees most affected by this fungus are:

  • Oaks including our state tree the Northern Red Oak.
  • Maples
  • Pines
  • Taxus which is an English yew shrub.
  • Fruit trees.

If you have ever seen a spruce with healthy green needles at the tips of the branches, but no needles further down the branch, welcome to needlecast. This fungus attaches itself to spruce trees, it has a strong preference for Blue Spruce trees and can attack the white spruce and other conifers, like pine and fir, that are also susceptible. The Norway spruce is resistance to the disease.

Needlecast takes time, usually about four seasons, to completely take hold of a tree but once the first signs of the disease begin to show on your tree it will become an obvious eyesore on your property. This fungus hits trees that are already stressed, either from drought, poor nutrients in the soil or too many trees planted together. Needlecast diseases of evergreens are caused by several fungi, but all the needlecast fungi form small structures on the infected needle in which thousands of spores form. These "fruiting structures" may be black, orange-red, or tan, depending upon the fungus.

Black knot is a serious disease of plum and cherry trees (Prunus species) throughout the United States. Black knot is a disease that gets progressively worse each year unless controlled, and it will eventually stunt or kill the tree.

As seen through the lens with a magnifying glass, there will be rows of small black dots. These dots are the fruiting bodies of the fungus, and they are a characteristic of the disease. This disease is spread by rainwater splashing the spores from infected needles to newly emerging needles in the spring. Pycnidia, the fungal fruiting bodies containing spores, begin forming in rows on infected needles during spring when moisture is high.


Trees exposed to stressed growth conditions like drought, winter problems, insect infestations like borers, or injured because of contact with a vehicle are more likely to develop the fungus. This root disease results from the colonization of trees and shrubs by fungi in the genus Armillaria. It is an incredibly durable fungus, being able to withstand extreme weather and temperatures. Removing soil from the base of the tree trunk you will be able to see the shoestring-like rhizomorphs attached to the tree roots. In an infected tree, you may find white feathery mats of fungus which fan out between the bark and the wood of the tree.

What’s the damage?

Armillaria can cause wood and root rot, which often goes unnoticed in trees. It’s well protected beneath the surface and can survive wildfires. Because it is in the root system of the tree it can travel to other trees. Armillaria root rot is found in urban and suburban areas of the state as well as in the forests and recreational areas in North Jersey and along the Delaware River. This fungus threatens many of the area's shade trees and conifers.


While there is no guaranteed treatment for this fungus, there are several steps you can take to minimize the issue.

  • Trees that are healthy can rebuild themselves and repair any damage caused by the fungus.
  • Watch your trees carefully for any signs of illness.
  • Take care of them during extreme weather such as droughts and reducing stress.
  • Use a professional tree service to diagnose and treat your tree.
  • If caught early, the soil around your trees can be treated with a good fungus, like Trichoderma, to combat destructive fungus spores such as Armillaria.

These are some ways to help protect your oaks against fungi such as Armillaria. Prevention and early detection are keys to ensuring that your trees won’t need removal because of disease.

Once the disease has spread throughout a tree root system, the tree must be removed and the stump ground down. This is to prevent the disease from jumping to other trees. Removing the tree from your property is the safest thing to do.

There are trees that are resistant to Armillaria root rot and some of them are locust, Japanese maple, tulip tree, sycamore, sweetgum, mulberry. Fruit trees include pecan, pear, and plum.

Although Armillaria may be resilient and almost unrecognizable, that doesn’t mean that your trees are helpless. Calling the experts at Advanced Tree Care is a step in the right direction of preserving your trees for years to come.