In 2020, the biggest walnut tree on the land started to show some signs of weakness.
We noticed that the bark was highly damaged by insects and through the premature autumn colouration and leaf drop we confirmed that it was seriously sick but we couldn’t identify the reason.
In autumn we found a cluster of yellow to honey-colored mushrooms at the base of the tree which gave us a first clue.
We found out that the tree was infected by a fungus called Armillaria Mellea, commonly known as honey mushroom or mushroom root rot.
This was bad news as Armillaria Mellea is a common worldwide pathogen of trees causing root rot, root-collar rot and butt rot. It’s often lethal for the tree especially in trees stressed by other factors.
Given that the signs of a weakened tree were quite obvious, our chances to save the tree were small, but we had to try anyway.
We got in contact with our colleagues from the Soil Food Web School and Dr. Elaine Ingham herself to start a treatment with another fungus called Trichoderma. This fungus is an effective biocontrol agent for a number of plant and tree fungal diseases.
The interesting particularity of this fungus is that it eats other fungi so it can help in removing Armillaria Mellea. In fact, Trichoderma is the only known treatment against a honey mushroom infection – there is no other substance or commercially available fungicide to effectively combat Armillaria Mellea.
According to the advice from Dr. Elaine Ingham, we first had to isolate the infected root system from the rest of the land by digging a 30cm deep trench around the root zone of the walnut tree as Armillaria Mellea can disperse naturally through the spread of rhizomorphs (rootlike structure) in the soil. Once a host is dying, the fungus will look for another host to colonize its root system.
Unfortunately, the tree was already in its final stage of life when we started applying Trichoderma and we couldn’t save it.
Nevertheless, the tree gave us a gift:
A more deepened understanding about a widely unknown aspect of the kingdom of mushrooms and some experience on how to fight Armillaria Mellea in a natural way.
Some months later, a friend put us in contact with Salvatore who is having problems with his olive trees. The way he described the symptoms of his olive trees suggested that he could be faced with the same problem. We paid him a visit to examine the trees and take some soil samples. From all the data and information collected, we found out that the olive trees were indeed infected by Armillaria Mellea.
Salvatore told us that a couple of local agronomists went to the land to check the trees and they suggested uprooting the trees, burning them, and planting new ones. They also recommended disinfecting the infected area with lime. He was clearly upset and disappointed as ¾ of his olive trees are affected by the pathogen and he wouldn’t be able to afford a labor and cost-intensive solution like that.
We elaborated a report explaining the data and suggested an action plan including a treatment with Trichoderma spores (pictures at the top and below).
Our suggested plan was split in 3 phases:
Defense – Attack – Recovery
- During the defense phase some actions are required to stop the spread of the fungus and protect the tree. For example to reduce humidity at the base of the tree by removing weeds and mulch around the trunk.
- The next phase is to apply Trichoderma spores to grow the only known fungus that can attack and eventually kill Armillaria Mellea. The treatment is done by pouring water containing Trichoderma spores in a trench around the drip line of the affected tree. This way, we target the most active part of the root zone where Trichoderma spores have more chances to establish a connection with the root of the tree prior to starting looking for other fungi.
- Last but not least, we will need to bring back to the soil the beneficial organisms that are responsible for providing nutrients and water to the tree and strengthen its immune system. This is particularly important in the case of beneficial fungi (mycorrhizal) as the Trichoderma treatment simply kills every other fungus during the treatment.
We feel grateful for Salvatore’s trust and we will continue working together to save his olive trees. At the same time, we keep learning about this sort of pathogenic fungus and we implement regenerative practices to restore the soils.
A win-win situation.
We will keep you posted on Social Media and through our Newsletter about the progress 🙂