The Honey Fungus - Armillaria mellea / gallica

Armillaria gallica / bulbosa

Armillaria gallica

To a gardener, Honey Fungus is one of the most feared fungi. If a shrub or tree is infected, its height is often reduced, foliage is sparse and the leaves that remain on the plants are stunted and yellow. Getting rid of it is a major problem. You have to remove as much of the stump as you can, sterilising all tools after use or try and dry out the soil (in NI?) to make life difficult for the fungus. The fungus often attacks trees or shrubs that have been weakened by some other attack, physical or biological, so the healthier the garden is the better. However it can also attack healthy specimens as well. I have spoken to people who have sprayed the area with urea to try and kill it with no success. 

If you think you might have Honey Fungus attacking one of your trees or shrubs, try to look just under a bit of bark about the root collar area and look for a dense white mat of mycelia. If it is there, it is probably Honey Fungus. Also look for the bootlaces or rhizomorphs by which it spreads. Fallen trees are often covered in these rhizomorphs and they can spread out from an infected tree by 60m or so looking for another tree to infect.

Armillaria rhizomorphs

But is this reputation justified in Northern Ireland? That depends on which species of Armillaria we find more commonly here. Typically, we have been recording anything that looks like the Honey Fungus as Armillaria mellea, but we now realise that we probably weren't looking close enough! The common species of Armillaria here and it is very common, is Armillaria gallica (see photograph at top of page) or Armillaria bulbosa as it is named in some books. This species is actually not so vicious and we probably don't have much of a problem here in Northern Ireland.  Armillaria mellea, the vicious species is more a southern species and doesn't like the cooler north as much. It is here, but we have to look a lot more to get a good idea of how common it is. To tell the two apart, look at their stems. Armillaria gallica or bulbosa has a distinctly bulbous base which I think is very obvious when young. Armillaria mellea (see photo below) has a much slenderer stem. This difference is not always obvious and the clearest way to tell them apart comes under the microscope as Armillaria gallica has clamps at the base of the basidia. 


See also this page on the NW Fungus Group website

Armillaria mellea

Armillaria mellea

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