By Tonihyne
United Kingdom 
I have a short beech hedge 35 yrs old and 10 feet high trimmed annually. There are two patches on one side which are brown and have not got new leaves. Just had hedged trimmed and examined those patches and there is a thick deposit like cotton wool mostly in & around the Y joints where branches and twigs divide and progressing up twigs. The deposit is not on the leaves. The leaves of those trees have got brown spots and brown along the margins. It is not powdery mildew or any other beech disease I can find on line. Any ideas. What can I do if anything.
14 Jul, 2014
Answers
Hopefully its just Beech scale, also called felted beech scale. Although the RHS says its not essential to treat for this infestation, recent research indicates that its often the precursor of Beech Bark Disease, a serious fungal infection, simply because the scale insect penetrates the bark, and the penetrated areas are then vulnerable to Beech Bark Disease. Unfortunately, with a simple infestation of scale, I wouldn't expect to see dead parts or affected leaves, so its possible your beech is already infected with Beech Bark Disease. Google both for more information.
15 Jul, 2014
Hi Toni and welcome to GoY. Could you add a photo to your question please.
15 Jul, 2014