What Are These Bumps on My Oak Tree Leaves?

From the moment they sprout in spring to the final drop in fall, leaves on our trees captivate us.

That’s why anytime leaves don’t look their best, we want to spring into action and help.

Our blog reader, Gwen, recently asked, “I believe insects have burrowed into the leaves of my burr oak tree, now they’re dying and turning orange. Is there a cure?”

If you also see bumpy, blistered oak leaves with a funky color, read on to learn why this is happening and what you can do.

Why You See Bumps or Round Balls on Oak Tree Leaves

Oak leaf blister disease and oak leaf gall are the top two culprits when it comes to problems with oak tree leaves. There are a few ways to tell them apart.

Oak Leaf Blister Symptoms

Trees suffering from oak leaf blister will develop raised spots scattered on the leaves. Underneath, leaves will feel slightly sunken or indented. That’s what was plaguing Gwen’s oak trees!

The blisters are first a pale green or orange and then eventually turn brown or black. Severely infected leaves will curl or drop early.

Galls on Oak Leaves

Galls are abnormal growths that crop up on trees after insects or mites settled in. They’re clusters of brown or orange balls that vary in size and cover tree leaves and branches.

Depending on the what insect is causing it, some galls are hairy while others are perfectly round and smooth.

What to Do About Bumps on Oak Leaves

Good news and bad news. Oak leaf blister and oak leaf gall cause little harm to trees. But both are ugly to look at–especially on your once-beautiful oak tree!

Luckily, infected trees typically bounce back with proper plant health care. Most of the time there’s no need for a chemical treatment.

If your tree has oak leaf blister:

• Keep the tree well-watered in hot, drought-like weather.
• Cover the tree with a ring of mulch in spring.
• Apply fertilizer right before winter to help boost health.
  

If your tree has oak leaf gall:

• When galls are in their early stage in spring, prune infected twigs.
• Rake and dispose of fallen leaves in autumn. This may help get rid of resting insects and mites that brought on the infestation.

If you suspect your tree needs extra attention, have your arborist see your oak tree in person!