Brown fuzz like growths on underside of Holm Oak leaf
No interactions present.
You're right that it's one of the two, but they can only be separated by identifying the mites (there was a discussion about this on the British Plant Gall Society forum a while back). The BPGS has access to experts to i.d. difficult specimens (or indeed the mites) and details (including how to package specimens) are given on www.british-galls.org.uk/verification.htm but I don't know if they'll only do so for members.
Thanks for the information - very useful indeed.
This is more likely to be Aceria ilicis (Eriophyes is now a synonym) than Aculops coulteri. So far as I am aware the latter has not been recorded in Britian.
It is true that A. ilicis is more likely, but A. coulteri has been recorded in Britain (though there's nothing on NBN) - see my previous message regarding a discussion within the Brit. Plant Gall Soc.
Lat/Lng: 51.9, -2.1
OS grid ref: SO9324