Coral spot

What you are looking at

Small raised cushions the colour of tinned salmon, a couple of millimetres across, studding a dead branch. There are usually a great many of them, packed close enough to make the wood look pink from a few paces. With age they darken through brick red towards black.

Before the pustules appear, the branch dies. A stem wilts in summer, the leaves brown and hang on rather than dropping, and the whole thing is dead by autumn while the rest of the plant carries on. The pink comes afterwards, on the wood that has already gone.

Japanese maples, magnolias, elaeagnus, figs, gooseberries and currants are where gardeners meet it most. It turns up on a great many other woody plants and on almost any dead wood lying about.

A weak parasite with an open door

Coral spot spends most of its life doing something useful. It is a decay fungus of dead wood, and on a pile of prunings or a dead stump it is getting on with the job.

What makes it a garden problem is that it will move from dead tissue into living tissue when a plant offers it the chance. A pruning stub that dies back, a snapped branch, a strimmer wound, a frost crack, or a plant already weakened by drought all give it a foothold. From there it works down into healthy wood and kills the branch.

That is why the same fungus is harmless on one plant and fatal to the maple beside it. The difference is whether there was a way in.

It also explains the single most overlooked source in a garden. Pea sticks kept from last year, bean poles cut from hazel, brushwood stacked behind the shed and a log pile against the border wall are all dead wood, and dead wood covered in pink cushions a metre from a young acer is a problem waiting to happen.

What to do about it

Cut the affected branch back into clean sound wood, well past the last pustule and past any staining, and do it as soon as you notice the dieback.

Look over the whole plant for stubs left from previous pruning and take them back to a bud or a collar.

Clear the dead wood out of the garden. Burn the prunings or take them away, and move the log pile and the pea sticks away from anything susceptible.

Keep the plant growing well. Mulch, water in a dry summer, feed in spring. A strong maple holds the line and a starved one does not.

Stop making wounds. Check ties, keep the strimmer away from stems, and prune cleanly.

Nothing sold to gardeners treats this, and nothing needs to. The fungus is everywhere and the management is entirely about not giving it a route in.

What it gets mistaken for

Honey fungus kills from the base upwards, with sheets of white fungal growth under the bark at ground level and black bootlaces in the soil. Coral spot works downwards from a wound on a branch.

Silver leaf turns the foliage a metallic silver and stains the wood purple-brown inside, with nothing visible on the outside of the bark.

Bacterial canker sinks and kills bark on plums and cherries and weeps amber gum.

Other Nectria species produce similar cankers on apple and beech with rings of callus around them and much smaller, redder fruiting bodies.

Orange algae and some lichens colour bark orange in damp shade without harming anything. Those are flat films rather than discrete raised cushions, and they sit on live bark as readily as dead.