Ers dechrau’r 1990au, mae’r clefyd Chalara fraxinea wedi taro’r rhan fwyaf o wledydd yng ngogledd Ewrop gan ladd coed ynn ifanc a pheri i goed aeddfed wywo.  Mae’r clefyd yn awr wedi cyrraedd Ynys Prydain ac yn fygythiad mawr i’r rhywogaeth bwysig hon.
Since the early 1990s Chalara fraxinea disease of ash has spread to most parts of northern Europe where it has caused death of young trees and the dieback of mature ash trees in many countries. It has now been found to be present in the UK and poses a serious threat to this important tree species.