How to Manage Pests

Pests in Gardens and Landscapes

Rhizopus rot (Leak)— Rhizopus spp.

Strawberry fruit with Rhizopus rot soften rapidly and collapse, leaking their contents. Under humid conditions, fluffy white mycelium forms on the surface of decayed fruit.

Identification

Rhizopus rot is often confused with gray mold. However, fruit infected with Rhizopus leaks its contents, whereas fruit infected with gray mold does not leak.

The fungal growth formed on Rhizopus-infected fruit can be distinguished from gray mold by examining it with a hand lens. Tiny but conspicuous, spherical spore-forming structures called sporangia are present, each one on the end of a hairlike stalk about 0.10 inch long. Sporangia are white when first formed and turn black as they mature. Botrytis does not form sporangia, although masses of spores resembling tiny clusters of grapes may sometimes be seen. Both Botrytis and Rhizopus can be present on the same fruit.

Life cycle

Rhizopus rot occurs primarily after harvest but may develop on ripe fruit in the garden. Species of Rhizopus survive on debris in the soil when host plants are not present. Spores are spread by wind and insects, and infection occurs only through wounds in ripe fruit. Rhizopus is not active below 41°F.

Solutions

Fruit decays can be kept to a minimum by using raised beds, plastic mulch to keep fruit from touching the soil, and drip or furrow irrigation to keep water off the foliage and fruit. Most important is to make sure plants are spaced far enough apart that there is good air circulation around the fruit. Dense plantings make a damp environment that favors fruit decay. In cooler locations, you can improve the air circulation around plants and fruit and reduce fruit disease problems by using stepped planter boxes that allow fruit to hang down over the sides. If sprinklers are used for strawberries, always water in the morning so that plants will dry off during the day.

Early infection of Rhizopus rot
Early infection of Rhizopus rot

Mycelium on Rhizopus infected fruit
Mycelium on Rhizopus infected fruit

Leaking of contents by infected fruit
Leaking of contents by infected fruit


Statewide IPM Program, Agriculture and Natural Resources, University of California
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