A Case History of Inonotus dryadeus
February 4, 2013
Root Rot often called White Root Rot or Weeping Conk is actually Inonotus dryadeus a very common problem with our large Willow Oaks in Charlotte, and I imagine around the South East US. It is a serious issue because many times trees are left standing that are hazardous and in danger of uprooting. I'm sure if you live in the wooded parts of town with the large willow oaks have seen these mushrooms at the base of some of the older trees. You should know something about this situation because these trees are potentially dangerous. The root systems of these trees have weakened and can fall or blow over.
What you see initially is a single mushroom. This is the fruiting body of the fungus. The fungus’s mycelium that is not seen is below ground eating away at the strength of the anchor roots of the tree. Commonly the mushroom is call White Root Rot, not because of the Cinnamon colored top, but because the white mycelium (fungus roots so to speak) is digesting the wood tissue. The scientific name is Inonotus dryadeus, and it is one of the polyporus fungi. If you turn one of these mushrooms upside down, you will observe "many" “small holes” on the bottom.
These mushrooms are usually located at ground level on older willow oaks. They fungae spores probably enter the tree from a previous wound such as created by a sidewalk, driveway, curb, or from lawn mower damage.
As the mushroom grows underground, it eventually destroys the root system. Sometimes the upper canopy will show signs of distress, and the tree is removed before it dies. Other times the tree will blow over from a violent wind storm, or ice storm. Since the tree is heaviest when it is in full leaf, and the ground is often saturated, early spring is the most vulnerable time for trees to uproot.
How could this affect you?
If you have one of these old willow oaks with this mushroom at the base anywhere within one hundred feet of your home, car or loved ones, then you need to know when or if it should be removed. My daughter used to complain because I illustrated points I was trying to make by telling her a story. So bear with me. Here’s mine.
We have lived in our home on Queens Road West for over forty years and originally had eight willow oaks all of which were probably planted by the architect /developer John Nolen. We have lost six of those Willow oaks to decay and only two remain. I noticed in 2008 that one of the large willow oaks in the front yard had a single mushroom at the base. I did not bother to photograph it then and thought that the tree was not a hazard at the time. I assumed I would have seven years or so to observe the mushrooms spread and watch the general health of the tree.
In 2010 I photographed it again during the summer which shows the previous season’s mushrooms. It was spreading across the trunk, and the tree otherwise looked healthy. We usually see these mushrooms fruit late August or September. In the fall of 2010 I saw no evidence of the fresh mushrooms which I thought was odd. Did they go away? Was there some seasonal various that caused them to not appear? I just did not know, but decided to keep a better eye on their progress. During the fall of the next season, I did not see any new fruiting bodies of the mushroom.
In the summer of 2012, based on the fact that I thought the tree was leaning, my wife and I decided to have the tree removed. The tree was a little thin and weak in the top or canopy, but in general it looked healthy. When we had it removed I asked David, who was the stump machine operator, to tell when he encountered dead wood as opposed to healthy live wood. The harder wood would be alive and any rotted wood would be soft and cut easily. He said he could detect the difference while cutting.. When David was finished, he said it was strange, there were no roots of the far side of the tree. He had started cutting the stump exactly opposite where the mushrooms had been.
I concluded that the roots that had previously anchored the tree on the far side had decayed in the moist soil over the past four years. After the stump chips were removed, I took a shovel and dug down all the way around the tree and marked the live wood with yellow marking flags. I placed one red flag where I found no roots and placed a second red flag around the circumference where the sound wood started again. Photo below
The soil between the two red flags had no live roots growing. The yellow flags do not come all the way around to the second red flag, but that is only because I was digging the area directly in front of the camera. Also if you look at the soil on the left there is fresh sawdust (stump cuttings) and on the right you see mostly dark soil. The live roots got in the way of the digging on the left and on the right it was easy to dig the soil and decayed roots.
At least 40% of these anchoring roots were destroyed by decay. .It turns out that I had made a good decision. The right kind of wind or ice storm could have caused the tree to fall over. Is this a typical situation for every case of White Root Rot or for that matter some other type of decay organism?
I think every situation should be analyzed, but delaying could be very dangerous. I observed White Root Rot every season for the 42 years I was in the tree maintenance business. I had one acquaintance tell me that they had a tree with this fungus growing on the trunk that had been in the tree for thirty years ever since they had moved into their house. I never saw that tree and do not know if the real identity of the root rot was Inonotus dryadeus .
There are less aggressive fungi so I don't really know if we were talking about the same organism. Over the years I developed the opinion that once this fungus appeared we had about seven years before the tree became hazardous; however, in the case I mentioned above, the entire episode took about three to four years from the time I first saw the fungus to the time we removed the tree.
Certainly, deciding how long to leave a tree standing once one spots the fungus is a question that requires some serious thought. The tree care industry could do some more research and pass this information on to the public. Unfortunately, much of this type of information is published in scientific publications and sometimes in trade magazines which the general public does not see. Meanwhile, if you see large mushrooms at the base of your tree, you should meet with a consulting or certified arborist to help you make a sound decision. Most reputable tree service companies in Charlotte have Certified Arborist on their staff.
Street trees in our older neighborhoods such as Plaza Midwood, Dilworth, and Myers Park have older trees that are often affected by these mushrooms. This is probably due to the fact that these trees are close to sidewalks and curbs. Alert Charlotte officials especially if you see advanced decay on street trees. The simplest way would be to contact City Landscape Management at 704-336-4262.
An article similar to this is being published in several neighborhood newsletters. If you are interested in using the article, just give credit
More photos and some details of this willow oak are located here