By Iris22
United Kingdom 
why is my Myrtle covered in brown spots? I bought it last year from Queen Victorias home on the Isle of Wight. Growing good in large pot but now every leaf has these brown marks.
6 May, 2012
Sounds like sooty mould which can sometimes be removed when sprayed with a jet of water.
This link will give you other possibilities;
http://www.clemson.edu/extension/hgic/pests/plant_pests/trees/hgic2002.html
6 May, 2012