I visited my weed tree a few days ago, before the onset of rain. It’s been very dry in London for the past few weeks, and the earth around this sycamore is parched and dusty. Even the weeds have died off..
On the tree itself, much seemed the same.. until I spotted red protrusions on some of the leaves. I had to clamber into the fork of the multi-stem to get photo. I tended to call these nail galls before, but actually those are more pointy and appear on lime trees, hence their Latin name Eriophyes tiliae. The ones on sycamore are Aceria macroryncha. The galls are caused by mites which feed on the fresh leaves, and each mite can stimulate a number of galls to be produced. In May, the mites will lay eggs into the galls, and the growing larvae will feed on the the lining of the galls. Having only known that these galls were caused by mites, I didn’t know anything about the lifecycle and behaviour before. Now I know, I’ll have a closer look at these galls to see if I can spot the small holes fringed with hairs on the underside of the leaves, through which the mites gain access to the galls to lay their eggs.
I’ll be keeping an eye open for the development of Tar Spot, a fungal disease which affects Sycamores in London. As yet, I’ve seen no sign on this tree.
If you haven’t already visited the Loose and Leafy blog, head over there for more tree following links.