How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Initial infections of Rhizopus fruit rot appear as discolored, water-soaked spots on fruit. These lesions enlarge rapidly, releasing enzymes that leave the berry limp, brown, and leaky. Under conditions of high relative humidity, the berry rapidly becomes covered with a coat of white mycelium and sporangiophores. The sporangiophores develop black, spherical sporangia, each containing thousands of spores. When disrupted, these sporulating berries release a cloud containing millions of spores. Rhizopus and mucor fruit rots closely resemble each other and may be difficult to differentiate in the field.

COMMENTS ON THE DISEASE

The fungus is an excellent saprophyte that lives on and helps break down decaying organic matter. It invades strawberries through wounds and secretes enzymes that degrade and kill the tissue ahead of the actual fungal growth. The fungus is active most of the year in California and survives cold periods as mycelium or spores on organic debris. Spores are airborne. The pathogen has a large host range and is prevalent worldwide.

MANAGEMENT

Rhizopus stops growing at temperatures below 46° to 50°F (8° to 10°C), so rapid postharvest cooling of fruit is essential for disease control. Field sanitation also is extremely important: do not leave discarded plant refuse or berries in the furrows, and be sure to remove all ripe fruit from the field. There are some benefits to the use of protective fungicides, but unless the disease is widespread throughout the field, this pathogen should not cause excessive damage.

Cultural Control
Field sanitation is extremely important. Handle fruit with care at all times. Remove all ripe fruit from the field at harvest. Be sure when fruit is being picked that the entire fruit is removed from the stem, not leaving behind the fleshy receptacle of the fruit as it can serve as a site for invasion by fungus. Cultivars with thick cuticles are less susceptible to Rhizopus fruit rot because they are better able to resist infection.

Organically Acceptable Methods
Sanitation, cultivar selection, and rapid postharvest cooling are acceptable for use in an organically certified crop.

Treatment Decisions
Fungicide treatment is not recommended.

PUBLICATION

UC IPM Pest Management Guidelines: Strawberry
UC ANR Publication 3468
Diseases
S. T. Koike, UC Cooperative Extension, Monterey Co.
W. D. Gubler, Plant Pathology, UC Davis
G. T. Browne, USDA Crops Pathology and Genetics, UC Davis

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