Symptoms and Signs
Alternaria fruit rot infections commonly begin in the orchard following rain during flowering and early fruit development. The fungus can grow inside the fruit without external decay symptoms. Infected fruit generally are lighter in weight and the rind may be slightly off-color, such as a paler red, and may show some brownish-red discoloration. In the later stages of infection, arils show a brown decay and black sporulation can be seen inside the fruit. In advanced stages of internal decay, the fruit's exterior shows some shriveling.
Comments on the Disease
Alternaria alternata and related species commonly present on plant surfaces and in dying or dead tissue 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 or wounded fruit with soil dust. Infections may also start from insect and bird punctures on fruit. While San Joaquin Valley research suggests that the petal fall stage is the most susceptible to infection, infection can occur throughout the 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. Cultural controls can help manage alternaria fruit rot:
- Use good orchard management practices, such as dust control and sanitation (removal of old fruit and dead branches), to reduce the incidence of the disease.
- Consider gently shaking the tree at the time of harvest to drop infected, healthy-appearing fruit to the ground.
- Avoid water stress and overwatering that may result in fruit cracking.
- Avoid packing diseased fruit by thoroughly sorting and grading pomegranates for discoloration and cracking.
|Common name||Amount per acre||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.|
|A.||POLYOXIN D ZINC SALT|
|MODE-OF-ACTION GROUP NUMBER1: 19|
|COMMENTS: A chitin biosynthesis inhibitor, which has medium resistance potential.|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.|
|1||Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode-of-action group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode-of-action group number; for fungicides with other group numbers, make no more than two consecutive applications before rotating to a fungicide with a different mode-of-action group number.|