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Despite not being native to our state, Colorado blue spruces (Picea pungens) are remarkably popular trees among Michigan homeowners. Given their manageable size, attractive growth habit, and stunning blue foliage, it’s easy to see why they’re so commonly planted in our area.
But unfortunately, they don’t always thrive in our area, given the way our climate and soil conditions differ so markedly from those in their natural range. Blue spruces have evolved to live within a very specific set of environmental conditions, and they often struggle when planted in areas that can’t duplicate them.
This manifests in different ways in different parts of the country, but here in Michigan, it often takes the form of Cytospora canker (Cytospora kunzei).
We’ll explain everything you need to know about this pathogen, the way it affects blue spruces, and what — if anything — you can do about it.
What Is Cytospora Canker?
Cytospora canker is a fungal pathogen that affects a few different tree species, though it’s most commonly associated with the Colorado blue spruce.
The fungus is often found living in the healthy branches of trees. It doesn’t usually trigger any physical symptoms or problems for the tree until drought, injury, or some other stressful event occurs. Once this happens, it becomes active and starts causing cankers to form on the bark.
Though it can kill trees at times, it is usually more of a chronic problem that stresses the tree further, makes it more vulnerable to secondary pests and pathogens, and diminishes the tree’s aesthetic charm.
Signs & Symptoms of Cytospora Canker in the Blue Spruce
Cytospora canker can cause a number of symptoms in blue spruces, including:
- Dead lower branches, which are often the first sign homeowners notice.
- The needles may turn brown and fall off the tree.
- White to pale blue patches of resin can appear on affected limbs.
- Dying branches higher in the canopy as the disease progresses.
- Areas of dead bark (cankers) may appear on branches.
- The bark will often darken in color near affected areas.
The disease’s namesake cankers disrupt the tree’s ability to transport water and nutrients to and from the affected limb, which further stresses the tree. These cankers will often grow over time and eventually girdle the entire branch.
Other Trees Susceptible to Cytospora Canker
While blue spruce is the primary host for Cytospora canker, other trees can occasionally contract the disease. A few of the most notable include:
- Balsam Fir (Abies balsamea)
- Fraser Fir (Abies fraseri)
- European Larch (Larix decidua)
- Japanese Larch (Larix kaempferi)
- American Larch (Larix laricina)
- Norway Spruce (Picea abies)
- White Spruce (Picea glauca)
- Black Spruce (Picea mariana)
- Jack Pine (Pinus banksiana)
- Red Pine (Pinus resinosa)
- Eastern White Pine (Pinus strobus)
- Douglas-fir (Pseudotsuga menziesii)
- Eastern Hemlock (Tsuga canadensis)
Protecting Your Blue Spruce Trees from Cytospora Canker
Unfortunately, there is no cure for trees already suffering from Cytospora canker. There are currently no effective fungicide treatments for Cytospora.
Instead, the best options center around prevention and providing additional support to trees that are already suffering from the disease.
A few of the most common and helpful strategies for protecting blue spruces include:
- Monitor blue spruces (and other susceptible species) regularly. By spotting the signs of Cytospora canker early, you can begin taking the steps needed to limit the disease’s progression.
- Provide supplemental water during droughts. Insufficient soil moisture is one of the leading stressors that can make blue spruces susceptible to Cytospora canker.
- Apply a layer of organic mulch over the root zone. Mulch helps retain soil moisture, provide organic matter to the root zone, and protect the roots from physical damage.
- Protect the tree from mechanical injuries. Wounds can provide infection sites for Cytospora and also place additional stress on the tree, so avoid damaging the trunk, branches, and roots.
- Prune out infected branches. Pruning infected branches can be helpful for limiting the spread of the disease, but it’s important that you sterilize your tools after cutting diseased wood.
There’s one last bit of advice we can share, though it is unlikely to be helpful in your current situation: Avoid planting blue spruce on unsuitable sites. This is especially true if you find it necessary to replace a blue spruce that’s already succumbed to Cytospora canker.
While many tree species are highly adaptable and can thrive in suboptimal planting sites, blue spruce trees often struggle when planted in marginal locations. They require full sunlight, low relative humidity, and moist but very well drained soil.
Cytospora Canker in Michigan: FAQ
Still have questions about Cytospora canker or the best way to protect your trees? We’ll share answers to some of the most common questions Michigan homeowners have below.
Can a blue spruce recover from Cytospora canker?
There is no cure for Cytospora canker, but many trees continue to survive for years, particularly when provided with proper support. With proper pruning, supplemental water, and soil support, it’s often possible to retain blue spruces long after they become infected.
Will Cytospora canker eventually kill my blue spruce?
Possibly, but Cytospora doesn’t usually kill trees outright. In fact, many blue spruces end up surviving for years after their initial infection, though they may lose branches or some of their initial beauty.
Can Cytospora canker spread to other trees on my property?
Yes. Though the disease is most problematic for blue spruces, it can spread to other susceptible species on your property.
What is the best time of year to prune branches affected by Cytospora canker?
The current environmental conditions are more important than the season when pruning Cytospora-infected branches. Avoid pruning during wet weather and instead prune when the foliage and wood are dry to help limit the spread of fungal spores.
Are there any fungicides that treat Cytospora canker?
Unfortunately, no. None of the fungicides commonly used to treat other fungal diseases are effective for Cytospora canker.
Is Cytospora canker more common in older blue spruce trees?
It depends on your definition of “older.” The disease may very well strike 50-year-old blue spruces, but it can also infect ones much younger than this. However, Cytospora generally does occur in blue spruce trees that are at least 15 to 20 years of age.
When should a blue spruce with Cytospora canker be removed?
Because many blue spruces will continue to survive with Cytospora infections for years, it’s usually wise to consult with an ISA-certified arborist before making a final decision. In many cases, with proper supportive care, infected spruce trees can be retained.
Let Us Help Provide the Support Your Trees Need
Whether you need help supporting a blue spruce with Cytospora canker, an ash tree suffering from EAB, or a hedge being destroyed by box moths, the plant health care experts at Longtree Tree Service can help.
Contact us today to schedule your free onsite evaluation. One of our ISA-certified arborists will assess your trees or shrubs and provide a recommendation and itemized estimate.
But don’t delay — most tree pests and diseases are easiest to treat when addressed early.
Sources and References
- MSU Extension – “Cytospora Canker”
Extension factsheet on Cytospora canker of spruce, covering symptom recognition (sunken branch cankers, white resin flow, progressive lower-branch dieback) and the cultural practices that limit spread on stressed Colorado blue spruce.
https://www.canr.msu.edu/resources/cytospora_canker - University of Minnesota Extension – “Cytospora Canker”
Extension guidance on identifying and managing Cytospora canker on spruce and other landscape trees, emphasizing tree stress reduction and pruning practices since no effective fungicide exists.
https://extension.umn.edu/garden-and-home/yard-and-garden/gardening-minnesota/yard-and-garden-problems/cytospora-canker - Missouri Botanical Garden – “Cytospora Canker”
Home-gardener overview of Cytospora canker across susceptible hosts, describing the disease cycle and the sanitation and vigor-maintenance steps that keep the opportunistic pathogen in check.
https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/insects-pests-and-problems/diseases/cankers/cytospora-canker - Forest Pathology – “Cytospora Canker”
Forest-pathology reference detailing the biology of Cytospora/Valsa canker fungi, their host range, and infection behavior on wounded and stressed woody hosts.
https://forestpathology.org/canker/cytospora/
