Sycamore bug?

Treehelpplease

I have two sycamore saplings growing. They were growing very, already up to 40cm tall and only a few months old. However, I noticed in the last few weeks the leaves have started discolour - turning a mix of brown and orange with white, flakey looking spots. I just assumed they were dying in autumn so I left them to fall off naturally, however they have yet to. I decided to pick off the very bad ones from the trunk, while leaving the healthier looking ones and the new growing leaves. However, while doing one of them I found what looked like a soft branch sticking between the trunk and one of the leaf stems. I tried to pull it off, assuming it was just part of a leaf I didn't pull off, but when I touched it it moved - it seemed to be alive. I got a small handheld clippers and when I touched it with that, it moved again, to slide around the blades. When I cut it, green goo came out. I dumped it but I'm wondering if it is a known bug or worm infecting sycamore trees? I don't really care if these two trees die as they're so young, however I'd rather be more informed so I don't accidentally spread it to any other sycamore trees around. Thank you

macraignil

Sounds like what I found before on a blackcurrant bush where a green twig actually was a caterpillar camouflaged as part of the plant. I posted a video of it here. Since you probably cut the caterpillar in half from what you describe doing I don't think you need to worry about spreading anything. I don't think these caterpillars are specific to a particular type of plant and not even sure to be honest what type of butterfly they turn into. Sycamore are very tough plants so I think your young trees should be fine.
Happy gardening!

Treehelpplease

Thank you for the reply. :-) Hopefully it's just that. These are some pictures of the leaves for further context. These are just the ones I left on, the ones I pulled off were worse