Armillaria, the Parasitic Fungus

This summer we planted my cedar garden in an area that is protected by wire and situated just below the cabin by the brook. My intention was to create a safe place for northern white cedar seedlings to thrive; they are slow growing second succession trees and hungry Whitetails (deer) feast on their tasty fronds during the winter. In this small area there are a number of dead trunks that are decomposing; two have been cut at ground level producing beautiful patterns. Moist rich fragrant woodland soil made planting each seedling easy.
 
Just to the right of the garden a thirty year old adult cedar (rough estimation) was spreading her shallow roots over this ground. Because mycorrhizal fungi live around the ‘mother’ tree I believed that these rootlets (hyphae) would seek out others, hopefully providing the little cedars with nutrients (I say she out of habit – some trees seem more female than others to me - and this was one of them-  but each cedar has male and female parts).
 
I have been watering my cedar garden every day since mid summer and I am pleased to note that none of the seedlings seem to have suffered transplanting stress. If all goes well, someday a small cedar grove may thrive here…

About a week ago (9/21) I was sitting among the cedars on a bench when I noticed that mushrooms were springing up around the base of the spruce that was last cut down because it was dead. Because we are suffering a severe drought I was surprised to see mushrooms, even here. I had only glimpsed one amanita, and one shelf mushroom this month so I found the fruiting odd. I broke a cap off and brought it back to the house to make a spore print as I researched the mushroom’s identity.
 
While waiting for the spore print I discovered that the mushroom was probably one of the species of Armillaria that appears growing out of the base of trees or stumps for only a few days a year in late September or early October.
 
The spore print was white, confirming my identification.
 
Oh dear.
 
I remembered Merlin Sheldrake’s remarks about Armillaria. These honey fungus were long lived and form some of the largest living organisms in the world. Armillaria ostoye/solipedes one of two most deadly parasitic Armillaria species covers more than three and a half square miles in Oregon’s Malheur National Forest and is more than 2500 years old and weighs hundreds of tons. Armillaria ostoyae started from a single spore too small to see without a microscope. It has been spreading its black shoestring filaments through the forest killing trees as it grows.
 
(This organism rivals Pando, the trembling giant who is a single aspen clone who is geneticially male. A forest of one he is a grove composed of 47,000 quivering aspen trees connected by a single root system).
 
Honey Mushrooms are not only circumpolar in the northern hemisphere, but are recognized as one of the most widely distributed mushrooms in the world as they can be found at the appropriate latitudes in the southern hemisphere as well.
 
Honey fungus is a "white rot" fungus, a pathogenic organism that affects trees shrubs and other plants. Honey fungus can grow on living, decaying and dead trees and plants.
At times the honey mushroom’s fungus is saprotrophic—that is, it decomposes the heartwood of plants, turning the non-living part of trunks and roots into soil, but this is a temporary state. Eventually the fungus gets hungry for more food.
 
Honey fungus spreads from living trees, dead and live roots and stumps by means of reddish brown to black root –like structures called rhizomorphs. These grow close to the soil surface and invade new roots or the place where the roots meet the trunks or stems. An infected tree will die once the fungus has girded it or after significant root damage has occurred. This can happen rapidly or take years.
 
Initial symptoms of honey fungus infection include shortage of spring leaves or dieback. Rhizomorphs appear under the bark and around the tree, and mushrooms grow in clusters from the infected plant in during September and October. Thins sheets of cream colored mycelium beneath the bark at the base of the trunk or stem indicate that honey fungus is the pathogen. The sheets often have a strong mushroom scent. On conifers honey fungus often exudes resin from cracks in the bark.
 
The mushroom, the reproductive structure of the fungus, grows on wood or roots, typically in small clusters that last only a few days (mine lasted four days). The mushrooms are yellowish brown and may range in shape from conical to having convex depressions in the center (mine were honey colored and displayed both of these shapes). The stalk or stipe may or may not have a ring (some of mine did; others did not). All ten Armillaria species have a white spore print. Some species of Armillaria are bioluminescent – they glow in the dark.
 
Of the ten species Armillaria mellea and ostoyae are the most aggressive killers. Armillaria gallica frequently infects plants that are suffering from environmental stress or other infections. One of the former grows in the mountains of New Mexico.
 
I was not able to determine what species of Armillaria I have growing in the cedar garden but I do know that there are two more dead trees in this small area, one a spruce and the other a maple.
 
Oddly, also in this one small area many tree seedlings – balsam, spruce, hemlock, white pine, maple - are sprouting and virtually all of them seem healthy. It may be that the fungus has yet to enter these plants?
 
I read that on the west coast that red cedar seems to have some immunity to honey fungus disease and because the northern white cedar and red cedar are related (Thuja) I wonder if my seedlings might have some protection from the invasion of this pathogen. These new world cedars are actually junipers.

Honey fungus is particularly damaging to lilac, privet, apple, many flowering cherries, willow, birch, walnut, cedars, and cypresses. Box elder, Californian black walnut and yew seem to be virtually immune. Other resistant species include fir, bamboo, hornbeam, beech, ash, junipers (hah, found this information after writing the above), larch, and oaks,

Symptoms of attack by Honey fungus include:
1. Yellowish-brown (honey) colored mushrooms, usually in clumps, on or near tree stumps or recently felled trees or dead plants. The mushrooms may not appear every year but when they do the spore print should be white.
2. Occasional death over the years of previously vigorous woody plants in a relatively small area.
3. The best indication of attack by Honey fungus is the presence of white fungal growth beneath the bark on roots and the collar portion of a dead or dying tree. Peel back a section of the bark from the lower trunk or upper roots. Honey fungus mycelium forms white or cream paper-like sheets sandwiched between the dead bark and underlying wood. The sheets have a strong mushroom smell.

Control of Honey fungus
The stumps and roots of dead trees are ideal breeding grounds for the fungus, therefore the most effective way to prevent the spread of the disease is to remove all dead stumps and roots from an affected area.

Do not replant on the site for one year and then replant with resistant species. Ironically as deadly as this fungus can be for trees and plants their fruiting bodies are considered to be delicious to eat. Honey Fungus are regarded as one of the best wild mushrooms by many, but they must be cooked thoroughly, and even so may cause gastric upset in some people. Don’t harvest honey mushrooms from spruce trees. They may make you ill.
 
I had no idea when I began this project that I was beginning an experiment. When I wrote to Merlin his response was that I had to wait and see. What will happen to the seedlings when they encounter the honey fungus… will they be able to resist infection?