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.
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.