The disease is found throughout Wales and while many trees will have been affected for several years, the progression of the disease, and the impact it has on the trees is variable.
Mae'r clefyd i'w ganfod ledled Cymru ac er y bydd llawer o goed wedi cael eu heffeithio ers sawl blwyddyn, mae cynnydd y clefyd, a'r effaith y mae'n ei gael ar y coed yn amrywio.