Honey fungus Armillaria mellea. By Neil Bromhall for rightplants App
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The honey referrers to the honey yellow-brown coloured mushrooms which appear in autumn. Mell being Latin for Honey.
The mushrooms are scaly like an armadillo. The toadstool stem has a collar-like ring and the gills are creamy white.
It is also known as boot-lace fungi because the rhizomorphs look like black bootlaces.
Armillaria mellea is a parasitic fungus that lives off trees, woody shrubs and perennials and is the most destructive fungal disease in the UK and is the gardeners’ nightmare.
The rhizomorphs grow relatively close to the surface – in the top 20cm but can go down as far as 85cm.
The rhizomorphs can spread up to 1m per year in light, sandy, loamy soils though the spread is slower in thick clay soil.
When the rhizomorphs penetrate the soil and come in contact with roots. They penetrate the roots and infect the new host plant. After the mycelium has colonised the dead wood underground, the hyphal strands form together to make the bootlace-like rhizomorph which then spread up the trunk and also underground to find new host plants.
Death can be quick or take several years. The mature apple tree in my new garden gave a fabulous display of flowers in spring then suddenly died.
Te only symptoms you may notice are foliage discolouration, dieback of branches, and early autumn leaf colour and leaf fall. Severe infection can cause the plant to ‘bleed’ or the bark to split just above ground level.
A sign of infection is resin exuding from cracks in the bark of conifers.
Some plants will give a final display of bloom and then suddenly die, as my apple tree did this year.
Black bootlace-like rhizomorphs can be found under the bark but another sign is the presence of thin sheets of cream coloured mycelium which has a strong smell of mushrooms.
There are no chemicals to control the fungi. The best way I’ve found to control the fungus spreading is by digging up the diseased plant with as many roots as possible and burning it.
Don’t plant a shrub or tree in the same position but in another part of the garden you burying a protective barrier made of plastic sheet up to 85cm deep and protruding 2-3cm above ground. The rhizomorphs can’t penetrate the plastic so the newly planted shrub should be safe inside its protective barrier.
Deep digging can help break up the rhizomorphs and limit its spread though digging a deep trench and lining it with a barrier made of plastic sheet might be more useful.
Digging a trench around an old infected plant can help as you’re breaking up and cutting through the rhizomorphs and disconnecting them from the host plant (in this case a dead Cherry tree).
Any infected roots and wood should be dug up, removed and burned.
It has been suggested that the white ash mixed with water and poured around plants suspected of ill health can help by restoring the plant to good health. It’s worth a try and maybe a good idea to do the same when planting a new tree or shrub.
Plants that are less prone to attack are:-
Acer negundo (Box elder) Juglans nigra (Black Walnut) Quercus cerris, Quercus ilex, Quercus rubra, Sorbus aria, Taxus (Yew)
Prone plants are:-
Acer, Aesculus, Betula (Birch( Buddleja, Ceanothus, Cedrus, Cotoneaster, x Cuprocyparis leylandii (Leyland cypress) Fagus Beech) Hydrangea, Julans, Ilex (Holly), Ligustrum (privet) Magnolia, Malus (Apple) Photinia, Prunus, Pyrus (Pear), Quercus, Rhododendron (Azalea) Ribes (Cuirrent) Rosa (Rose), Salix (Willow) Sorbus except, Syringa (Lilac), Viburnum
There are two main species found in gardens Armillaria mellea and Armillaria gallica
A gallica are large and produce easily visible rhizomorphs quite often found in compost heaps.
The list below gives species that are fairly resistant but not immune :
The true firs, Abies species J
uniper, Juniperus species
Tree of Heaven, Ailanthus altissima
Larch, Larix species
Common Box, Buxus sempervirens
Liquidambar, Liquidambar styraciflua
Incense cedar,
Calocedrus decurrens
Southern beech,
Nothofagus species
Hornbeam,
Carpinus betula
London plane, Platanus X hispanica
Indian
Bean Tree, Catalpa bignonioides
Cherry Laurel, Prunus laurocerasus
The Thorns, Crataegus species
Blackthorn, Prunus spinosa
Beech,
Fagus sylvatica
Douglas fir, Pseudotsuga menziesii
Ash, Fraxinus excelsior
Oaks, Quercus speces
Holly,
Ilex aquifolium
False Acacia, Robinia pseudoacacia
Limes,
Tilia species
The list below gives species that are highly resistant :
Box Elder,
Acer negundo
American Black Walnut,
Juglans hindsii
English Yew, Taxus baccata
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