What’s That on My Tree?

It’s a beautiful summer day, you’re walking through the yard with your morning coffee, when you spot something on your tree.

It’s crusty…fuzzy…or…oozy? 

Cue the internal panic.

“Was that there yesterday?” 

“Do I need to call someone? 

Or should I Google it first?”

If you have trees in your yard, chances are, once in a while, you find weird things on them. And honestly, not all of them are bad. Some are totally normal. Some are early warning signs. And some? Well, they mean it’s time to call in the experts.

This is your go-to guide for all those “what’s-that-on-my-tree” moments. Let’s get into it. 

Photo credits to unsplash.com

Weird Stuff Growing On Your Tree (And Whether You Should Panic)

1. What’s that black, green, or crusty stuff on my bark?

If your tree looks like it’s growing a beard, it’s probably lichen or moss. These crusty or fuzzy patches may look ominous, but are mostly harmless. In fact, lichen is a sign of good air quality. They don’t steal nutrients or strangle your tree.

If the bark underneath is soft, crumbling, or easily coming off, that could be a sign of a fungal infection or decay hiding beneath the lichen. That’s when you call in an arborist.

2. Is lichen bad for my tree?

No. Lichen is just an epiphyte, meaning it lives on your tree, but doesn’t feed off it. That said, if lichen is growing heavily and your tree looks otherwise unwell, it could be a sign that the canopy is thinning and the tree is declining.

3. What’s that white powdery coating on the leaves?

That’s probably powdery mildew, a fungal disease that thrives in shady, damp spots. It gives leaves a ghostly, dusty look and can cause distortion or leaf drop if left unchecked.

Your best bet is to improve airflow by strategic pruning, avoid watering the leaves, and provide your tree with a bit more sunlight if possible.

4. Why are mushrooms growing at the base?

Mushrooms near the trunk are a red flag. They often indicate decaying roots or internal rot, especially if they appear repeatedly. Some species grow on already dead wood, but others feed off live tissue, weakening the tree’s structure. If your tree is leaning, brittle, or showing canopy dieback, call an arborist immediately.

5. Why is sap leaking?

Sap isn’t always bad, but sometimes it requires professional diagnosis. Trees often release it naturally from wounds. But it could be a reaction to borers, bacterial infection, or physical injury. Sudden sap weeping often indicates that your tree is stressed and requires support.

Leaf Troubles and Insect Activity

6. Why do my tree leaves have holes? 

Photo credits to unsplash.com

If your tree looks like it’s been through a paper shredder, you’ve probably got caterpillars, leaf beetles, or leaf miners in the mix. The good news: A few holes here and there are usually just cosmetic, and there’s no need to panic.

The bad news: If your tree gets defoliated season after season, it becomes stressed and vulnerable to disease. If that’s happening, it may be time to intervene.

7. Why are my tree’s leaves yellow in the middle of summer?

Unless it’s autumn (and even then, it should be subtle), yellowing leaves in July are a red flag. Common causes include:

• Iron chlorosis: A nutrient deficiency, often from poor iron uptake.
• Compacted soil: Tree roots can’t breathe.
• Overwatering or poor drainage: Your tree roots could be drowning. 

8. Why are there bumps on my branches or leaves?

Those weird little bumps are likely scale insects or galls.

Galls are caused by tiny insects laying eggs. These are mostly harmless and often just cosmetic.

Scale, on the other hand, is more serious. These pests suck the life (literally) from your tree and multiply quickly.

If you see sticky residue or black sooty mould, scale might be the culprit.

9. What’s the difference between aphids and scale insects?

Both are sap-sucking pests, but they behave differently in that aphids form visible clusters, often on new growth. Scale, on the other hand, looks like stationary bumps. They are easy to miss but persistent. Both leave behind honeydew that attracts ants and leads to sooty mould build-up on leaves.

10. Brown or black leaves—what does that mean?

If your tree’s leaves are turning brown or black, it could be:

• Anthracnose (a fungal disease), especially in wet springs
• Sunscald from intense summer heat
• Drought stress or poor watering habits

Bark, Branches, and Overall Tree Health

11. Why is my tree’s bark peeling? Is that normal?

Photo credits to unsplash.com

Sometimes, yes. Trees like birch, sycamore, and silver maple naturally shed bark as they grow. But when bark is peeling in large sections, revealing decay or insect damage, it’s no longer normal. 

If the exposed wood is soft, cracked, or discoloured, call an arborist to assess for disease or structural instability.

12. My tree is losing bark and leaking sap.

Sticky sap combined with bark loss is rarely a coincidence. This combination can indicate canker disease, boring insects, or mechanical damage. Remember, sap is your tree’s defence system. If it’s gushing or smells bad, it’s time for a professional tree health check.

13. Is my tree dying? How can I tell?

A sudden decline may indicate trauma or disease, while a gradual decline might point to soil, root, or care issues. The tell-tale signs of a declining tree include:

• Dead or bare branches high up
• Sparse or thinning canopy
• Fungus or mushrooms at the base
• Epicormic sprouts (shoots growing from the trunk—a stress signal)

14. What does a diseased tree look like?

There’s no one-size-fits-all answer, but look out for:

• Yellowing, wilting, slow growth, swelling, or leaf spots
• Cracks, decay, or softness in the trunk or roots

Knowing When to Call the Pros

We get it. You don’t want to overreact to a few leaf spots or a sticky branch. But when your tree starts throwing out real warning signs, waiting it out may not be the right call.

For minor issues like aphids, powdery mildew, or slight leaf yellowing, you may be able to manage with a bit of research and elbow grease—consider pruning, proper watering, or eco-friendly sprays.

But if you notice any of these, don’t DIY it:

• Mushrooms or fungal conks at the base
• Bark peeling off in chunks
• Cracks, lean, or sudden canopy thinning
• Insect problems that keep coming back
• Dead limbs falling (or at risk of falling)

Seen something weird? It might be best to put your mind at ease. 

If your tree is showing signs of stress, decay, or just looks… off, don’t guess. Get a second opinion. At Green Drop Trees, our ISA-certified arborists know exactly what to look for, whether it’s a hidden pest problem or early-stage disease.

We offer comprehensive tree healthcare services throughout Edmonton, Calgary, Red Deer, Saskatoon, Winnipeg, and Regina. 

From odd leaf spots to leaning giants, we’ve seen it all, and we know what to do next.

Get a free tree care estimate today, and let’s keep your trees healthy, safe, and thriving without the mystery.