M. fructicola cannot in principle be distinguished from the other brown rot fungi except by
laboratory examination (see below). It tends to occur more often on peaches and nectarines,
while M. laxa favours apricots and almonds. However, both species can occur on all
Prunus spp. and are difficult to differentiate (Wilson & Ogawa, 1979). M. fructigena is
more characteristically found on apples and pears. On fruit, a soft brown rot (sometimes
turning black in apple) is followed by the appearance of conidial pustules on the surface of
the fruit (especially on cut surfaces). These are grey-coloured in M. fructicola and M. laxa,
but distinctly buff-coloured when freshly formed in M. fructigena. In low humidity,
pustules may not develop; instead, the whole fruit shrivels into a wrinkled mummy.
Infected blossoms and leaves turn brown and wither, producing a typical blighted
appearance. Stem infections lead to brown, collapsed areas (cankers), often with an
accumulation of surface gum. Tufts of conidiophores appear on these infected tissues under
humid conditions.