Tree problems · Disease

Cytospora canker: signs and what to do

Cytospora canker is a tree disease, often seen on colorado blue spruce, aspen and cottonwood. Look for: on spruce, a branch that dies back above a canker, often in an upward spiral.

General information, not a diagnosis. A certified arborist or your county extension office can confirm.

Disease
Colorado blue spruce (the most often hit)
Other spruces and firs
Aspen and cottonwood
Many other stressed trees, including maple and birch

Signs to look for

Tick what you see. More ticks make it more likely, but only an on-site look can confirm.

On spruce, a branch that dies back above a canker, often in an upward spiral
Spruce needles that turn purple, then brown, then drop
Whitish or bluish resin on cankered spruce branches
On broadleaf trees, sunken or discolored patches of bark on branches or trunks
Small black, pimple-like dots in the dead bark, which can push out orange threads of spores in wet weather
Oozing liquid from the bark of some trees, such as aspen

0 of 6 signs ticked. Ticks stay in this browser only.

Season

The fungus lives through winter in the cankers. Spores are released in wet weather and enter fresh wounds on trees that are already stressed. Damage grows over several seasons.

How it spreads

Spores spread in splashing rain and wind and may also be carried by insects, birds and tools. They enter through wounds from pruning, mowing, weed trimming, hail or storms.

Where it is found

Cytospora canker is found in many parts of the United States on many kinds of trees. Check your state official map; ranges change.

Official sources

What to do

1
Look for dead branches with resin, sunken bark or black dots. Take close photos of the bark and the needles or leaves.
2
Think about what is stressing the tree: drought, compacted soil, poor drainage, root damage, or a site that is too hot or wet.
3
Prune off dead and cankered branches in dry weather. On spruce, cut back to a healthy branch union.
4
Wipe your pruning tools with 70% alcohol or a household disinfectant between every cut.
5
Water deeply in dry spells, mulch to the drip line but keep mulch away from the trunk, and avoid trunk wounds from mowers and trimmers.
6
Do not pay for a spray as a cure. University guides say fungicide is not effective for this disease.

Safety first: do not climb, do not cut near power lines and do not use a chainsaw on storm-loaded wood. Call the utility for downed lines and 911 if anyone is in danger.

Prevention

Cytospora mainly attacks stressed trees, so good care is the best protection. Match the tree to the site. Space spruces so branches do not overlap and air can dry the canopy. Protect trunks and roots from damage. Ask a nursery about dwarf or better-suited varieties if you want to plant blue spruce.

When to call a pro

Call a certified arborist if a spruce has many dying branches, if a trunk has a large canker, or if a cottonwood or aspen is losing limbs near a house, driveway or line. Pruning and removing large trees is work for a trained and insured crew.

Not sure who to call? Read how to hire a tree service or check is my tree dangerous?

Trees it affects

Usually seen on: Colorado blue spruce (the most often hit), Other spruces and firs, Aspen and cottonwood, Many other stressed trees, including maple and birch.

See all species in our tree library, or pick a tougher tree with the tree picker.

For tree companies

How to explain cytospora canker to a customer

Explain that this disease follows stress, so fixing the stress matters as much as pruning. Be clear that no spray cures it, and do not sell one as a fix. Offer a plan: clean pruning in dry weather, better watering and mulch, and honest advice if the tree is too far gone.

Send this page to the customer after your visit so they can read the signs in plain words. See also selling plant health care and the job photo checklist.

Questions

What is Cytospora canker?

It is a fungus disease that kills patches of bark and then whole branches. It attacks spruce, aspen, cottonwood and many other trees.

Why is my blue spruce dying from the bottom up?

Cytospora canker is one common cause, but there are others, such as needle cast diseases. A pro or your extension office can tell them apart.

Does the fungus kill healthy trees?

It mostly attacks trees that are stressed by drought, wounds, poor soil or a bad site. Healthy trees usually resist it better.

Can I save the tree?

Sometimes, if the problem is only on a few branches. Prune them off in dry weather and reduce the stress. A tree with large trunk cankers may not recover.

Is there a spray that works?

University guides say fungicide is not effective for this disease. Care for the tree and clean pruning are what help.

When should I prune?

Prune dead and cankered branches in dry weather, because spores spread in wet weather. Disinfect your tools between cuts.

Can it spread to my other trees?

The spores can spread to wounds on other stressed trees. Removing dead branches and caring for nearby trees lowers the risk.

Should I plant another blue spruce?

Ask a local nursery or your extension office. In some areas, other spruces or dwarf varieties are a safer pick.

Can Lirevon diagnose cytospora canker on my tree?

No. Lirevon is a remote marketing team for tree service companies and does not do tree work. This page is general information, not a diagnosis. A certified arborist or your county extension office can confirm what is wrong with your tree.

How do I find a good local pro for this?

Search Google Maps for certified arborists or tree services near you, read their reviews and ask for proof of insurance. Get two or three written quotes. Our guide on how to hire a tree service lists the questions to ask.

When customers spot cytospora canker, they call

Make sure someone answers. Missed-call text-back, lead follow-up, booking and review requests, set up for you. See our services and pricing.

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