Honey fungus is the common name of several species of fungi within the genus Armillaria. Honey fungus spreads underground, attacking and killing the roots of perennial plants and then decaying the dead wood. It is the most destructive fungal disease in UK gardens.
Honey fungus can attack many woody and herbaceous perennials. No plants are completely immune, but some have very good resistance, such as Juglans nigra (black walnut) and Acer negundo (box elder).
Acer (except A. negundo), Aesculus, Betula (birch), Buddleja, Ceanothus, Cedrus, Cotoneaster, × Cuprocyparis leylandii (leyland cypress), Fagus (beech), Hydrangea, Juglans (except J. nigra), Ilex (holly), Ligustrum (privet), Magnolia, Malus (apple), Photinia, Prunus (except P. spinosus), Pyrus (pear), Quercus (except Q. cerris, Q. ilex, and Q. rubra), Rhododendron (azalea), Ribes (currant), Rosa, Salix (willow), Sorbus (except S. aria), Syringa (lilac) and Viburnum are all particularly susceptible to honey fungus.