September 5th – Whilst I obsess over galls on oaks and wild roses, other shrubs and trees have their own problems. Here on Clayhanger Common, this sycamore tree is affected by sycamore mites and tar spot fungus.
The curious leaf growths form on the leaf like a gall from the point at which mites feed on the leaf by the same mechanism that other gall insects imply – in the case of these tiny mites, their saliva corrupts the lead cell DNA to grow into a gall.
On the underside of the leaf, a tiny, fur lined aperture into the gall is used by the mite after it has grown to lay its eggs, and the gall is eaten by the hatchling.
This leaf also has tar spot fungus.
Neither harm the host tree to any extent.