It is thought to have arrived in the UK around 20 years ago from fungal spores carried by wind from the continent and from infected tree planting stock imported from mainland Europe.
Credir iddo gyrraedd y DU tuag 20 mlynedd yn ôl o sborau ffyngaidd a gariwyd gan wynt o’r cyfandir a thrwy stoc plannu coed wedi’i heintio a fewnforiwyd o dir mawr Ewrop.