Oaks are legendary for their strength, but even these giants have a few weak spots. If you want to keep your tree standing tall for generations, you’ve got to know what to look out for. Here’s the lowdown on the most common oak diseases, how to spot them, and—most importantly—how to fix them so your tree stays in tip-top shape.
Keep an eye out for these common oak troublemakers:
- Oak Bracket Fungi (Oak Phellinus)
- Powdery Mildew
- Bacterial or Fungal Cankers (Tree Cancer)
How to Spot and Treat Oak Bracket Fungi
If you see tough, woody shelf-like growths popping out of your oak’s trunk, you’re likely looking at bracket fungi. These “conks” are a clear giveaway. The tricky part? You usually can’t just hack them off without causing even more damage to the trunk. Generally, a perfectly healthy oak can fend these off, so the best defense is a good offense. Make sure your tree is getting the nutrients it needs; a well-fed tree is much better at keeping the fungus from spreading further.
How to Spot and Treat Powdery Mildew
Powdery mildew is pretty easy to identify—it looks exactly like someone dusted the fresh leaves of your oak with flour or powdered sugar. While it might look harmless at first, if left unchecked, those leaves will eventually wither and drop off. You definitely want to step in before the infection takes over the whole tree.
To help your oak bounce back, focus on consistent watering and proper fertilization. Also, here’s a pro tip: always rake up and bag any fallen, infected leaves. Toss them in the trash rather than the compost pile so the spores don’t hang around to reinfect your garden next year.
How to Spot and Treat Tree Cankers
Tree “cancer” or cankers are usually caused by fungi that sneak in through open wounds or pruning cuts in the bark. Once inside, the infection spreads through the trunk, often creating a swollen, cushion-like growth. This is serious business—it literally drains the tree’s energy and can become life-threatening if ignored.
If you spot a canker, it’s time to perform some surgery. You’ll need to prune the affected area, making sure to cut back until you hit healthy, white wood to ensure the fungus is completely gone. Bag up those trimmings and get them off your property. Finally, apply a wound sealant to the fresh cut. This acts like a bandage, protecting the tree from new infections while it heals up.
