Friday, January 11, 2013

Mummy Berry

Mummy berry is a plant disease caused the fungus Monilinia vaccinii-corymbosi.  The fungus overwinters on the ground, and in spring produces a cup-shaped mushroom that releases spores.  These spores infect and kill emerging leaf shoots, causing the shoot blight (primary) phase of the disease.  Blighted shoots then produce a second type of spore that is carried by insects to the flowers, where fruit (secondary) infection takes place.  The end result is “mummies” – berries that do not turn blue, but instead turn pink or salmon-colored and fall to the ground.  Mummy berry can be controlled with fungicides, through the use of resistant cultivars, by removal of infected fruit, and by mulching to bury any mummies remaining on the ground.  Shown below are a few photos of mummy berry at different times of the year:  

 The October photo below shows infected fruit in winter.  All berry tissue has sloughed away, leaving behind a hard, hollow structure consisting entirely of dormant fungal tissue.

Dormant mummies

In spring, dormant mummies germinate and produce tiny brown cup-shaped mushrooms called apothecia.  These mummy cups (shown below) contain millions of spores (ascospores) that spread and infect new leaf shoots.  This stage occurs in February and March in eastern NC.

Three apothecia emerging from a single infected berry

Spores from apothecia infect new emerging leaf shoots.  This primary or leaf shoot infection occurs in March as shoots begin to emerge.  Infected shoots continue to develop and elongate, then quickly wilt and turn brown, first along the midrib of one or more leaves, then dying completely.  Infected shoots produce masses of the second spore stage, visible as a gray ash-like mass on the wilted shoot.  Infected shoots are usually visible in late March and April in eastern NC.
Wilting and browning along leaf ribs   

Infected shoot with a gray mass of spores

Multiple infections can defoliate a bush

 Fruit infection occurs when spores from infected leaf shoots are carried by insects to open flowers.  Spores germinate and enter the flower through the pollination pathway and infect the developing ovules.  Infected green berries appear normal until harvest, then turn a pinkish-tan color rather than blue, and drop prematurely.
Cutaway showing white fungal growth inside the fruit
Infected and healthy 'Croatan' fruit at harvest

Infected berries (mummies) fall to the ground and unless removed or buried, will emerge the following to re-infect the bush.
Enlarge to see infected fruit underneath this 'Gupton' bush