Symptoms and Signs
Alternaria rot, also known as surface mold, contact spot, or Alternaria internal rot, is a limiting factor in the production of figs for fresh market or for canning. All cultivars are susceptible, but the disease is most severe on Kadota, Conadria, and Calimyrna.
Surface mold caused by Cladosporium herbarum occurs on both green and ripe fruit, but tends to be more common on green fruit. The lesions usually occur in areas of fruit contact. Initially they are small, olive-green specks; as they enlarge the infected area turns yellowish olive and becomes sunken.
Rain or dew when figs are ripening will result in surface spotting. These spots are up to 0.2 inch in diameter, are light brown to black in color, sunken, and distributed over the entire surface of the fruit.
Alternaria is primarily a problem on ripe fruit, especially when rains occur during harvest. The first symptoms of Alternaria fruit rot are water-soaked areas, usually developing on the surface where two or three figs touch. These lesions soon are covered with dark green spores. Alternaria rot also develops as black fungal mats inside the cavity of Calimyrna and Conadria figs, beginning at the eye (ostiole) end.
Comments on the Disease
Alternaria alternata, Ulocladium altum, and Cladosporium herbarum commonly occur on plant surfaces or in dying or dead tissues of plants. The pathogens overwinter on plant debris in or on the soil. After sporulation, the spores become airborne. The fungi can be carried inside fruit as conidia and/or along with soil dust.
Rot in Kadota is reduced by picking fruit before it is overripe. Clean picking boxes and containers also reduce rot during storage. Reducing dust in the fig orchards may also limit the disease as well as reduce spider mite populations.