Season: Autumn

A guide to tree fungi

We frequently come across concerns from customers over fungi found on or near garden trees, this page will aim to address and alleviate some of these worries.

I am sure we all recall our school day Biology lessons on the Carbon and Nitrogen cycles that explain how nutrients are recycled in our natural environment. Fungi are a key component in this cycle, they play an essential role in breaking down organic matter to produce nitrates and carbon dioxide that re enter the nutrient cycle to allow our biosphere to continue operating. Fungi are therefore not something unusual to see in your garden, they can come in a wide range of colours and forms for many people they can be seen as quite attractive.

Honey fungus (Armillaria)

In terms of trees the presence of fungal diseases can create a weakened and/or unstable form, so monitoring of the health of your trees is advised. The spores that cause these diseases are spread in a variety of forms including through the air, via insects and in dead leaves. Many fungi exploit the vascular system within the tree that move water and nutrients around, as they grow they extend root like threads (hyphae) into the wood; these fungi are hard to spot as they work within the tree. Other types of fungi grow fruiting bodies on damaged areas like snapped branches, rootplate areas or on leaves, as such these can be a little easier to spot and identify.

Tips to avoid active fungal activity
  1. Fungi love damp areas so try to avoid planting a tree in an area of waterlogged soils, most trees favour well drained soils.
  2. Keep your tree in good health. Just like humans a good diet (regular fertiliser applications) and watering in dry months keeps your tree in tip top vitality and improves its chances to avoid fungal activity.
  3. Remove dead and diseased limbs as soon as you observe them especially in the winter months, this slows the spread of fungi through the tree ( do ensure your pruning tools are cleaned after use to avoid spreading the diseases across trees).
  4. Where leaves have been diseased we advise collecting them in the autumn and disposing of them away from your garden at council recycling depots or via incineration.

Many issues are raised over the use of watering or spraying fungicides to control the spread of fungal activity. Do ensure that you have correctly identified the fungus and apply the fungicide wearing appropriate protection for your eyes, lungs and exposed skin to avoid reactions and illness.

Honey fungus (Armillaria)

More than any other parasitic fungus this one is the most common one we encounter in SW London. They often grow in clumps as a yellow brown mushroom on the surface and white cream paper like sheets under the bark affecting many types of trees and shrubs including conifers, cedars, willow, birch, cotoneaster, plum, apple and cherry trees. The fungus can spread to surrounding trees via rhizomorphs (thread like strands) in the roots in some trees it may not kill the tree but it may weaken it so an inspection by qualified arborists is recommended.

Treatments are available such as Armillatox sprays several times a year around root collar areas but these cannot contend with large area infestations, the best option is to remove the tree and stump when a severe infestation is identified. The replacement trees or shrubs should have a good resistance to Honey fungus (eg. Yew ,Oak, Juniper, Laurel, Acacia, Beech and Ash).

In summary the best advice I can give is to give your garden trees the best opportunities for a healthy life with regular care and monitoring. If in doubt get free professional advice and don't worry fungi are a part of the natural assemblage of life!