Thes wrote:
Emrys Davies wrote:
deepdigger wrote...

I've an oak tree, not mature, about 12-14" thick at the base of
the trunk. Quite a lot of the leaves are going brown - the upper
surfaces look normal, except for brown patches of course, but
the lower surfaces are covered in patches of "stuff". Imagine
a miniature umbrella, open, without the handle, with the spike
dug into the underneath of the leaf. Now imagine many of these
per leaf, some mature looking browny spots, some new-looking
green ones, of smaller size. The diameter of the larger spots
must be about 1/6" (just over 4mm). These spots, or scales, are
held onto the leaf by the central "spike", and can be levered
off with the point of my pen-knife.

Here's an attempt at ASCII art, may not come out properly unless
you're using a fixed-width font (poss. not even then!):

################################ - leaf
__|__ _|_ _|_ - things
/ \ / \

Mature -- immature
brown green

The umbrella shape is rather exaggerated.

What sort of nasty are these??? Any help much appreciated!

http://images.google.com/images?q=oa...=Google+Search

None of those pictures look anything like what is described
though. They almost all show oak leaf blister which is doesn't
seem to be the OPs problem.

I'm curious to see if anyone can identify this rather bizarre
sounding gremlin.

Thank you Emrys, Thes - it isn't oak leaf blister, these
things are like a somewhat concave disc on a little stalk
which attaches to the leaf. Break the stalk and the disc
pops off. They are quite closely-spaced on some leaves,
which are going brown.