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Phytophthora fruit rot: black circular area on an avocado fruit caused by Phytophthora cinnamomi, identical to symptoms commonly caused by P. citricola.

Avocado

Phytophthora Fruit Rot

Pathogen: Phytophthora citricola

(Reviewed 1/07, updated 1/07)

In this Guideline:


SYMPTOMS AND SIGNS

Diseased fruit have a distinct circular black area that usually occurs near the bottom or lowest spot on the fruit. Internally, the rot extends into the flesh, darkening it in the same pattern as on the affected surface. Affected fruit are often touching the soil or are hanging on low branches. Most damage occurs within 3 feet of the ground.

COMMENTS ON THE DISEASE

Phytophthora fruit rot is caused by Phytophthora spp., usually P. citricola, the same fungus that causes Phytophthora canker and collar rot. Phytophthora fruit rot is usually of minor importance in California. Most damage occurs after prolonged wet conditions, the same situation that favors anthracnose. In contrast to anthracnose, which is primarily a postharvest problem, Phytophthora fruit rot infections often become obvious while fruit is still hanging on the tree, as well as causing decay after harvest.

MANAGEMENT

The most common cause of infection is believed to be the splashing of Phytophthora propagules from the soil surface to the fruit during heavy rain or sprinkler irrigation. Prune lower limbs so they are 2 to 3 feet from the ground. Maintain a thick layer of mulch to hasten decomposition of fungi on soil. Consider removing and disposing of fruit lying on the ground because the fungus sporulates on dropped fruit. Prune out dead limbs and twigs and dispose of dead wood and old fruit away from avocado trees.

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Avocado
UC ANR Publication 3436
Diseases
B. A. Faber, UC Cooperative Extension, Santa Barbara/Ventura counties
A. Eskalen, Plant Pathology, UC Riverside
G. S. Bender, UC Cooperative Extension, San Diego County
Acknowledgment for contributions to Diseases:
H. D. Ohr (emeritus), Plant Pathology, UC Riverside
J. A. Menge, Plant Pathology, UC Riverside
L. J. Marais, Plant Pathology, UC Davis
R. Hofshi, Hofshi Foundation, Fallbrook, CA
J. S. Semancik, Plant Pathology, UC Riverside
J. A. Downer, UC Cooperative Extension, Ventura County
U. C. Kodira, Plant Pathology, UC Davis

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