Diagnosing Rhizopus rot of peaches
Bill Shane, Michigan State University Extension
Rhizopus causes a brown-colored rot with a loose skin, unlike the relatively
firmer brown fruit rot. Rhizopus is primarily a disease of overripe fruit in
storage, particularly if the storage temperature is above 40 F.. Brown rot shows
up as a fruit rot before and after harvest. Rhizopus form grey-black sporangiophores
on the surface of fruit.
Infection in the early stages of fruit ripening by Rhizopus requires injury to open the peach skin. On ripe fruit Rhizopus rot can spread from fruit to fruit without injury at the point of contact. With Rhizopus, fungal growth is rapid at 80 F but ceases at 40 F.
Rhizopus rot usually can be managed by storing fruit below 40 F and using picking equipment and boxes. Rhizopus tends to be a problem on overripe fruit. Botran has efficacy against Rhizopus rot and can be sprayed up to 10 days before harvest (check the label).
Figure 1. Whiskery appearance of Rhizopus rot on peaches in storage.
The peaches develop a white fungal net, followed by the
appearance of black spore-bearing structures.
Figure 2. Rhizopus rot of peach showing the skin disintegration
and sloughing off in the early stages of infection.
Figure 3. Brown rot of peach fruit showing the fluffy brown spores
typical of the disease.