Why Are My Swedish Aspens Dying from the Top Down?

Swedish aspens are known for their sturdiness and fast growth, but they also have a weakness. In Alberta’s climate, it’s not uncommon to see these trees begin to die from the top down, even when the lower half still looks healthy. 

This kind of crown dieback is more than just cosmetic. In many cases, it signals a serious fungal infection we call Hypoxylon canker. Let’s talk more about this.

What Top-Down Dieback Really Means

When the upper branches of your tree begin to die, it’s called crown dieback. You might first notice fewer leaves at the top, or branches that turn brittle and grey. Sometimes the rest of the tree still looks green and healthy, but don’t let that fool you.

Crown dieback is often the first visible sign of something more serious happening inside the tree.

It often starts slowly. You might notice fewer leaves near the top of your tree, or branches that don’t bud out in spring. As the season goes on, the upper crown becomes thin, brittle, or bare; sometimes with smaller, discoloured leaves or no new growth at all.

In many cases, the lower half of the tree still looks green and healthy, making the decline easy to overlook until the damage becomes more obvious. Left unchecked, the dieback will continue to move downward year after year, eventually compromising the entire tree.

Understanding Hypoxylon Canker

The most common cause of this dieback in Swedish aspens is Hypoxylon canker. This fungal infection enters the tree through wounds in the bark (wounds that are often caused by pruning, wind damage, or harsh weather).

Once inside, it travels up the tree, blocking the flow of nutrients and eventually killing the upper branches. It’s sneaky, and by the time you see symptoms at the top, the infection is already well underway.

Signs of Hypoxylon canker include:

• Progressive dieback in the crown
• Bark that looks rough, cracked, or stained
• Oozing sap or dark patches along the trunk
• Sudden limb death, even in summer
• White or grey fungal growth appearing beneath the bark or in cankered areas

Can It Be Stopped?

There’s no chemical cure for Hypoxylon canker, but there are ways to slow it down and protect the rest of your yard. Here’s what our ISA-certified arborists would typically do:

• Remove infected limbs as soon as possible with proper pruning tools
• Improve soil conditions by fertilization (our RootBoost service is great here) to strengthen the tree’s natural defences against the pathogen.
• Monitor nearby trees for similar symptoms and avoid overcrowding
• Sanitize pruning tools between cuts to prevent cross-contamination

Can I Prevent This from Happening Again?

Yes, while you can’t completely eliminate the risk, you can lower it significantly with some good tree care habits:

• Plant the right tree in the right place. Swedish aspens need well-drained soil and space to breathe.
• Avoid unnecessary stress. Deep water during dry periods, protect roots, and keep lawn equipment from damaging bark.
• Avoid pruning during wet or humid conditions, which can increase disease spread.
• Avoid over-pruning, especially in spring and summer when fungal spores are active.
• Minimize wounds from mowers, shovels, or other tools.
• Water during drought periods and keep the root zone mulched (but not buried!).

Final Thoughts

Watching your Swedish aspen decline from the top down can be frustrating. But the earlier you spot the signs, the better your chances of managing the issue, or at least preventing it from spreading to other trees in your yard.

In some cases, tree removal may be the best long-term solution, especially if the tree is in decline and near others that are still healthy.

Our ISA-certified arborists provide comprehensive Tree Health Care services to evaluate your tree’s condition and recommend the right plan of action. We’re happy to take a look. Contact us today to book a FREE tree assessment.