The fungus spreads through airborne spores, these are released by fruiting bodies which emerge on previously infected leaves, often found in the litter layer around the infected ash tree.
Caiff y rhain eu rhyddhau gan ffrwythgyrff sy'n dod i'r amlwg ar ddail a oedd wedi'u heintio o'r blaen, a geir yn aml yn yr haen sbwriel o amgylch yr onnen heintiedig.