Symptoms and Signs
Avocado fruit and stem-end rots are 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 the 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. Avocado fruit rot is caused by several Botryosphaeriaceae genera and species. The same group of fungi can cause avocado branch canker and dieback.
These pathogens spread by wind-blown or water-splashed spores produced in or on cankers, dead twigs and branches, 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 avocado fruit rot closely resembles that from ANTHRACNOSE and fruit damaged by these pathogens are usually culled and lumped together in the packing house. Anthracnose produces pink sporulation on the fruit surface, in contrast with the grayish mycelium from avocado fruit rot.
Use good sanitation and optimal cultural practices to minimize avocado fruit rot.
- Prune out dead limbs and twigs. Dispose of dead wood and old fruit away from 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.
- Provide sufficient irrigation with appropriate placement of high quality water. Maintain a thick layer of mulch under canopies to hasten decomposition of pathogen propagules. Do not harvest during or soon after rain; allow trees and fruit to dry before harvesting. Minimize the interval from harvest until fruit is placed into cold storage at the packing house; prompt cold storage reduces disease incidence.
- Follow the same postharvest handling instructions discussed in ANTHRACNOSE.
- Fruit should be picked by clipping rather than snapping the pedicles. Clippers should be frequently sterilized using a dilution (e.g., 1:10) of household bleach.