What is Honey Fungus?

Honey fungus is a term used to collectively describe several different species of fungi in the genus Armillaria, which attack and kill the roots of many varieties of trees and shrubs. The fungus gets its name from the honey-coloured mushrooms, which pop up in late summer and autumn. It resides in the soil and targets the roots of plants, slowly weakening the system until the plant is unable to survive.

Common in the UK, honey fungus in trees is a significant concern because it is the most destructive fungal disease in UK gardens. This means early detection and intervention is crucial for plant health and garden maintenance.

 

How Do I Identify Honey Fungus?

When in late summer & autumn it can sometimes be easy to identify due to their clusters of honey-coloured toadstools around the base of trees or affected shrubs, however, it becomes more challenging when these are not present.

However, honey fungus identification when the toadstools are not present is still possible, but it requires a little more work. You can do this by looking for white fungal growth between the bark and wood, by peeling away the bark from the stem at ground level and look for strings of white mycelium. If you can see this, then the tree/ plant is infected.

One other symptom is the presence of ‘bootlace-like’ fungal growths known as rhizomorphs, which appear red or purple at first, and then mature to black.

 

 

What Is Affected by Honey Fungus?

Honey Fungus is native to the UK; however, it doesn’t present as much of a problem in the wild where it is competing with rival fungi, keeping its growth, and spread in check.

The issues arise in gardens and other areas that are managed, where fungi are not normally tolerated, removing Honey Fungus’ natural competitors. This gives an advantage to the pest fungi which can take hold quickly and to devastating effects.

Honey fungus threatens most woody and herbaceous perennials, such as birch, hydrangea, privet, apple, pear, magnolia, and beech. Particularly susceptible plants include viburnum, willow, roses, and flowering currant.

Many perennial herbaceous and woody plants can be attacked and while certain plants are rarely reported to be impacted, none are immune to all threats.

 

How Long Does Honey Fungus Stay in the Soil?

It can live in the soil for many years, even if there’s no plant to attack. Its longevity makes it a persistent issue, and thus understanding its lifespan is crucial for effective honey fungus treatment and control. Conditions such as the type of soil, presence of host plants, and environmental factors influence its survival and growth in UK gardens.

However, if all the infected trees and shrubs are removed, along with all their roots, then one year is the suggested time frame to wait before replanting the area.

 

 

 

Does Honey Fungus Always Spread?

Unfortunately, honey fungus does always spread, and it can spread at a distance of 1m per year and infect nearby shrubs and trees with alarming speed

It spreads through long, black, root-like structures called rhizomorphs. These structures allow the fungus to travel across soil and infect adjacent plants. However, that is not the only way this fungus spreads. The RHS is conducting ongoing research and early indications suggest that spores from the mushrooms of Armillaria mellea are more important in spreading the fungus than previously thought.

“The genetic variability found between samples of the fungus taken from different areas of the garden at RHS Wisley indicates that many of the initial infections arose from spores (although once established in a particular area the fungus will still then spread between adjacent plants via rhizomorphs or root-to-root contact).” – RHS

Since it is parasitic, it can exist for a long time if it has material to feed on. Unlike most fungi, honey fungus can live on its host tree dead or alive, meaning when it kills its host, it doesn’t deplete its food source. This, when combined with its ability to grow underground with ease means this fungus can spread over large areas. In fact, an Armillaria has formed what is thought to be the largest living single organism on the planet and has been reported at 3.4 square miles in size and thousands of years old!

 

Is Honey Fungus Dangerous?

Honey fungus can be incredibly destructive to garden plants and landscapes. It not only damages the aesthetic value of gardens but also impacts biodiversity. Its existence poses risks to the healthy growth and survival of plants, where it causes decay and widespread damage.

The degree of damage that different species of honey fungus inflict on plants varies. While some species just restrict development or destroy weak plants, the more aggressive species can kill otherwise healthy plants. This means that it might not be essential to try to get rid of the fungus; but instead concentrate on keeping your plants healthy while living with it.

 

 

 

How Do I Get Rid of Honey Fungus?

Honey fungus treatment is a complex issue with a combination of preventive and control measures recommended. There are currently tests underway providing positive results from the use of Trichoderma however, the only current option to be completely sure of removal is to dig out the infected plant & its roots and dispose of it. This should kill the bootlace rhizomorphs that spread out from the host plant, but if the fungus has already infected other plants, then they will need to be removed as well.

It can be helpful to seek professional guidance to choose the best approach based on the specific conditions of the garden and the extent of the infection. Different treatments may be required based on the severity and the plants affected, the particular species, making a tailored approach necessary for effective management.

 

There are other ways to help prevent the spread which include:

• Removing a layer of soil around the base of plant stems – trees and shrubs planted too deeply are more likely to be affected
• Removing as much of the infected plant, including the roots and soil, as possible. Don’t leave stumps
• Removing plants growing around the affected plant, particularly in a hedge
• Digging the soil to root out and break up infected roots or rhizomorphs
• Avoiding planting anything back into the soil for a year, to kill off the fungus
• Replanting with less susceptible woody plants
• Recording where you’ve found honey fungus, to map which areas of soil are affected

 

Finally, the last option to treat Honey fungus is Avengelus Trichoderma from MycoSolutions. Trichoderma is a group of helpful soil organisms that form a close symbiosis with plant roots. Since they require the same soil nutrients as the pest fungi, Trichoderma can prevent the growth and reproduction of hazardous fungi and displace them. Trichoderma Atrobrunneum is highly competitive for food and space and grows much quicker than wood decay fungi. This limits space and other resources to wood decay fungi, making it a fierce competitor for pest fungi.

Not only that, but Trichoderma has mycoparasitic tendencies and will kill off and break down other wood decay fungi such as Honey Fungus to gain nutrition. Trichoderma can also cause the induction of systemic resistance which is where the plant’s natural defence mechanisms are stimulated, leading to enhanced resistance against a wide variety of pathogens. Finally, the presence of Trichoderma can enhance the overall defence mechanisms of the plant, making it more robust and capable of dealing with environmental stresses.

If you want to find out more about Avengelus Trichoderma then you can read our blog here, or you can check out Avengelus Trichoderma here!