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UC Pest Management Guidelines


Avocado decayed by Dothiorella fruit rot, caused by Dothiorella gregaria.

Avocado

Dothiorella Fruit Rot

Pathogens: Botryosphaeria spp. and Fusicoccum spp.

(Reviewed 1/07, updated 6/10)

In this Guideline:


SYMPTOMS AND SIGNS

Dothiorella fruit rot is usually not obvious while fruit is on the tree. Small, superficial lesions can develop on fruit in the grove, but the disease usually is apparent only on fruit that is very overmature, hanging on dead limbs, or dropped on the ground.

Infections usually become active after the fruit is picked and starts to soften. Initially lesions are small, irregular brown to reddish discolorations on the peel. Under the peel, brown streaks running lengthwise in flesh may be observed because decay initially spreads along vascular bundles in the fruit. Small, purplish brown spots may appear on any part of the fruit, most often at the stem end. As fruit ages, the surface lesions gradually enlarge and become sunken and black. Fruit shrivels, and the black surface can become covered with grayish brown fungal mycelium and spores. Decay then spreads throughout the entire fruit, causing the flesh to turn brown and watery with an offensive odor.

COMMENTS ON THE DISEASE

Postharvest rots are a relatively minor problem of avocados in California. Dothiorella fruit rot is caused by several Botryosphaeria and Fusicoccum species. Neofusicoccum luteum and Botryosphaeria dothidea are common causes.Disease was formerly attributed to Dothiorella gregaria, hence the name Dothiorella fruit rot. Several Botryosphaeria, Diplodia, and Fusicoccum spp. fungi can cause Dothiorella fruit rot, canker, or leaf and stem blight.

These pathogens spread by wind blown or water splashed spores produced in or on cankers, dead twigs, and dying fruit and leaves. Spores infect through wounds and lenticels (tiny natural openings) on fruit. Infection occurs in the grove, but disease usually is not obvious until after fruit is picked and starts to ripen.

Damage from Dothiorella fruit rot closely resembles that from anthracnose and stem end rot, and fruit damaged by these pathogens are usually culled and lumped together in the packing house. During its early stages, Dothiorella fruit rot lesions can occur anywhere on the avocado skin, while stem end rot initially occurs only near the narrow end of fruit, where decay begins under the button. Anthracnose produces pink sporulation on the fruit surface, in contrast with the grayish mycelium from Dothiorella fruit rot.

MANAGEMENT

Use good sanitation and optimal cultural practices to minimize fruit rots. Prune out dead limbs and twigs. Dispose of dead wood and old fruit away from avocado trees. Prune and harvest only during dry conditions. Correct environmental and nutritional stresses, and minimize other diseases and disorders that injure bark, fruit, or leaves. For example, anything that causes a large number of leaves to develop necrosis will cause fruit decay spores to become abundant on those leaves and spread to infect nearby fruit. Provide sufficient irrigation with appropriate placement of high quality water to minimize this and many other avocado problems. Follow the same postharvest handling instructions for fruit as discussed in the ANTHRACNOSE section.

IMPORTANT LINKS

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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