How to Manage Pests
UC Pest Management Guidelines
Alternaria Fruit Rot
Pathogens: Alternaria alternata and related species
(Reviewed 6/11, updated 6/11)
In this Guideline:
SYMPTOMS AND SIGNS
Alternaria fruit rot infections most commonly begin in the orchard following rain during flowering and early fruit development. The fungus may grow within the fruit without external symptoms. Infected fruit generally are lighter in weight and slightly off-color such as a paler red and may show some brownish-red discoloration.
COMMENTS ON THE DISEASE
Alternaria alternata and related species commonly occur on plant surfaces and in dying or dead tissues of plants. The pathogens overwinter on plant debris in or on the soil and in mummified fruit. The spores are airborne and can be carried to the flowers with soil dust. Infections may also start from insect and bird punctures on fruit. Research in the San Joaquin Valley showed that the petal fall stage seems to be the most susceptible stage when most of the infection occurs. However, infection can occur throughout the long bloom and fruit development periods.
Estimated losses are usually less than 1% but can be up to 6%.
Because the fruit crown covers the blossom tissues preharvest sprays are generally ineffective. Good orchard management practices, such as dust control and sanitation (removal of old fruit and dead branches), may reduce the incidence of the disease. Infected, healthy-appearing fruit may be dropped to the ground by gently shaking the tree at the time of harvest. Avoid water stress and overwatering that may result in fruit cracking.
Thorough sorting and grading of pomegranates for discoloration and cracking can help to avoid packing diseased fruit.
UC IPM Pest Management Guidelines: