Soft, collapsed strawberries that begin to mold can be a sign of rhizopus rot.
By David Strickland and Kerik Cox
Cornell AgriTech
Berry Disease Snapshot: Rhizopus Rot of Strawberry (Leak)
Causal pathogen: Rhizopus stolonifer, R. sexualis
When to watch for it: During the fruit-ripening period
First line of defense: At harvest, rapidly cool harvested fruit below 45°F
Summary:
Primarily a postharvest rot, Rhizopus rot may also occur in the field on ripe fruit. Modern storage and shipping have reduced this disease’s incidence worldwide, but it may readily appear if fruit are not cared for properly. Fruits infected with Rhizopus spp. appear slightly discolored, gradually turning light brown. The fruits rapidly soften and collapse, allowing their juices to leak out. Under humid conditions, white fluffy mycelium with large black sporangia appear. Rhizopus spp. can successfully overwinter on leftover plant material and in soil.
Protective broad-spectrum fungicides can be used to control Rhizopus rot in the field. Rhizopus spp. can only infect wounded fruit, so a vigilant insecticide program to manage fruit-feeding insects is encouraged. At harvest, Rhizopus rot is best controlled by rapidly cooling berries and maintaining storage temperatures below 45°F.