Cytospora canker

Cytospora and Leucostoma spp.

also called Leucostoma canker, Perennial canker

The named canker of spruce, peach and poplar: sunken bark, amber or white resin bleeding from it, and branches dying back one at a time from the bottom up.

Fungus Serious Airborne sporesRain splashSpread on tools & hands Spreads to neighbors

What you'll see

A sunken, discolored patch of bark, often with a distinct raised callus ridge around it where the tree has tried to wall it off.
Amber gum on peach and plum, or chalky white resin on spruce, running down the bark from the lesion.
On spruce, lower branches browning and dying one at a time while the top of the tree looks fine.
Pinhead black pimples in the dead bark, oozing orange tendrils of spores in wet weather.
Whole branches girdled and dead beyond the canker, with the needles or leaves hanging on brown.

Why it happens

A weak fungus that cannot get into a healthy tree at all. It enters only through wounds and dying tissue — a pruning cut, a mower scrape, a winter crack, a sunscald, a bark split from drought — and then spreads slowly in the wood beneath the bark. Everything about it is opportunistic, which is why it follows stress rather than causing it.

Drought-stressed, transplant-shocked, sun-scalded or root-damaged trees are what it takes. Colorado blue spruce planted too close together in a hot open site is the classic North American case, and peach trees after a hard winter are the other.

Treating it

There is no cure and no spray. Prune out cankered branches in dry weather, cutting well back into sound wood.
Disinfect the saw between cuts with alcohol; you can carry the spores yourself.
Do not prune spruce or stone fruit in wet weather, when the spore tendrils are out.
Water the tree deeply in dry spells and mulch the root zone — the real treatment is removing the stress.
Take out a spruce that has lost more than half its branches; it will not come back and it is a spore source.

Keeping it away

Plant spruce with room, in the right site, and do not line them up as a tight screen.
Avoid wounding the trunk with mowers and strimmers, which is how a great many cankers start.
Water young and newly planted trees through drought and mulch to keep the roots cool.
Prune stone fruit in late winter or early summer, never in the autumn.
Paint or wrap the trunks of young thin-barked trees against winter sunscald where that is a local problem.

Who gets it

Spruce, especially Colorado blue; peach, plum, cherry and apricot; poplar, aspen and willow.