Cytospora canker

What it is

A fungal canker disease that enters through wounds and stress

Trees affected

Aspen, cottonwood and poplar, spruce, apple, cherry, birch, silver maple

Where in our area

Planted trees on valley lots and Tahoe-elevation aspen and spruce, about 4,000 to 7,100 feet

Key sign

Sunken dead bark with tiny black bumps; orange tendrils in damp weather

Trigger

Drought, root injury, compaction, pruning wounds, sunscald

Cytospora is a weak pathogen: it usually gets in only when a tree is already under stress. Colorado State Extension names drought, root damage from construction, compacted soil and line trimmer injury among the causes. This page covers what to look for, which trees, what an arborist checks and when pruning or removal is the answer.

What does Cytospora canker look like?

On aspen the first sign is often an orange to blackish patch in the bark, and Colorado State describes the colors as running from fluorescent orange to a wet, oozing orange-black. The patch is sunken, the inner bark darkens and may smell foul, and tiny pimple-like black bumps, the spore structures, dot the dead area. In wet weather, orange coiled tendrils can emerge.

On spruce, look for a sunken, gall-like area on a lower limb with gray, oozing edges; needles above it turn brown and fall. On peaches and cherries, the sign is gummy sap. On any of them the limb above the canker dies back.

• Sunken bark, often orange to dark
• Black pinhead bumps in the dead area
• Oozing or gummy patches
• Dead limbs above the canker

Which trees and which elevations?

Colorado State Extension lists aspen, cottonwood and other poplars, spruce, apple, cherry, birch and silver maple as hosts. In our area that is quaking aspen, Fremont cottonwood, Colorado blue spruce, silver maple, white birch and fruit trees.

Valley lots at 4,000 to 5,100 feet carry most of the planted hosts, with the Truckee Meadows and Carson Valley cottonwoods the largest. At Tahoe, aspen and blue spruce growing in yards at 6,243 to 7,126 feet are the ones to watch. Pine, juniper, hackberry and linden are listed as less susceptible.

Why do trees get it?

The fungus spreads in rain, wind and on insects or birds and gets in through wounds. Colorado State Extension says it mostly attacks trees weakened by drought, crowding, temperature extremes, transplant shock, poor pruning, sunscald or mechanical injury. In a dry climate, drought is the common thread; see drought stress and dieback and sunscald and frost cracks.

The trigger is what stresses the host, so an arborist looks at the cause as well as the canker.

What does an arborist check?

The arborist checks whether the canker is on a small limb or on the trunk, how far around the trunk it has spread, how much of the crown is dead and whether other stress is present, such as root cuts or soil compaction.

• Canker size and location, limb or trunk
• How much of the trunk's circumference it covers
• Dead crown and dieback pattern
• Wounds from mowers, trimmers or construction
• Trees or buildings below

When is pruning or removal the answer?

On a small limb, the answer is pruning. Colorado State suggests cutting one to two inches into healthy tissue, leaving no stubs, cleaning the tools between cuts and pruning only in dry weather, since wet bark spreads the fungus. Dead and dying branches come off.

On the trunk it is different. The Colorado State guide says cankers that girdle the trunk cannot be reversed, and severely infected trees should be removed. That is the usual answer for an aspen or cottonwood with a trunk canker near a house; see tree removal and is my tree dead or dying.

What does Battle Born Tree Service do about Cytospora canker?

Call 775.232.8243 or use the estimate form on this page. An ISA Certified Arborist looks at the tree on site, explains what is wrong and tells you whether the job is pruning out cankered limbs or removal. Credential WE-11728A is held by one of our two certified arborists. We identify the problem, prune out dead or hazardous wood and remove trees that cannot be saved; we do not spray, inject, fertilize or apply products.