What is growing on my tree?

May 24, 2009 7:56 AM

What are these red, spiky... "things" growing on the leaves of my linden tree? Link to pictures inside.

Picture 1
Picture 2

Just noticed them this (Memorial Day) weekend. They're just a few mm long, on maybe 5-10% of the tree. It's a young tree, planted 3 years ago from nursery stock.

I'm wondering if this could be a danger to the tree, or just something that can harmlessly live on the tree with no ill effects.

posted by Steve3 to home & garden (6 comments total)

They look something like the wasp galls in this thread.
posted by jquinby at 8:01 AM on May 24

I see these on trees all the time. I'm pretty sure it's a wasp that lays its eggs in the leaves.
They don't seem to be too debilitating.
posted by dunkadunc at 8:02 AM on May 24

Aha! Your tree likely has spindle galls. There are some treatments for them, but they seem to be Mostly Harmless.
posted by jquinby at 8:04 AM on May 24

They might be caused by mites.
posted by weapons-grade pandemonium at 8:14 AM on May 24

That's a leaf gall caused by an eriophyid mite, Eriophyes tiliae. The saliva of the mite causes a cell proliferation in the leaf tissue, leading to the creation of a nice little home for the mite. Google "nail gall" for more details. These are harmless, luckily, because the mites are hard to control, due to the "house" they've built themselves, which protects them from most miticides. On a small tree I'd recommend pulling off and destoying all the galled leaves if it bothers you aesthetically, but on a large tree I'd just ignor it. Or use it as a conversation starter.
posted by acrasis at 8:20 AM on May 24

Glad to know they're not a threat to the tree. Thanks, acrasis and others.
posted by Steve3 at 10:16 AM on May 24