Pocket plum disease

 This summer there have been some spectacular local outbreaks of pocket plum disease, affecting sloes on blackthorn on the Durham coast near Hawthorn dene  and bird cherry fruits in Weardale. It's caused by the fungus Taphrina pruni, which induces the fruits to swell, become spongy and fill with watery fluid. In bird cherry (bottom picture) the normally spherical, shiny black fruits become banana-shaped. No seeds are formed inside these deformed fruits, instead there is an empty 'pocket'.

Attack of the killer bootlaces

This strange black network, that grew under the bark of this pine tree when it was alive, identifies the fungus that killed it - honey fungus Armillaria mellea.

Honey fungus is perhaps the most notorious of all fungal tree killers, not just of forest trees but also specimen trees of many species in gardens and arboreta.

The fungus kills the host by producing this network of rhizomorphs - bundles of hyphae that look like boot laces. They digest the living tissues between the bark and the water-conducting xylem that forms the woody core of the tree. The victim in this photo is a beech tree.

The rhizomorphs are doing their deadly work well before the fungal fruiting bodies appear. Often the first symptoms are individual branches of the tree dying, but it can take years to completely kill the tree. Often the roots are killed and then it topples in a gale. Meanwhile the rhizomorphs also grow downwards over the roots and out through the soil, until they find roots of a neighbouring tree that they can invade. 

Heterobasidion annosum - a notorious, tree-killing bracket fungus

We found this impressive specimen of the root rot bracket fungus Heterobasidion annosum in Hamsterley Forest at the weekend. The roots of the Norway spruce that it was growing on will have been largely destroyed by the time the fungal fructification reaches this stage.

The bracket was actively releasing spores - notice the dense white covering on the ground under the bracket. They are often dispersed by soil animals.

Root rot is one of the most damaging tree pathogens and the surrounding trees, as well as this one, are likely to be fatally infected.