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Thursday, January 9, 2014

Citrus Alternaria Brown Spot Disease ID with PICTURES

 Alternaria Brown Spot
  • Caused by the fungus Alternaria alternata
  • Found on young fruit, leaves and twigs
  • Brown to black spots surrounded by a yellow halo
  • Affects Dancy tangerines, Minneola tangelos, Murcotts, Orlando tangelo, Nova tangelo, Lee tangelo and Sunburst tangerine
  • Does not affect oranges; may affect grapefruit if located next to highly infected tangelos or tangerines
  • http://www.crec.ifas.ufl.edu/extension/canker/mistaken.shtml


    • Use Copper Fungicide to control this disease. The first spray should be applied when the spring flush leaves are 1/4 -1/2 expanded. The second spray should be applied when the leaves approach full expansion to reduce infection on the fruit. Another spray should be scheduled about 4 weeks later or shortly after petal fall. From April though June, spray applications may be needed as often as every 2-4 weeks depending on the frequency and amount of rainfall. 
    • http://edis.ifas.ufl.edu/hs141

      • Mature fruit will be okay to eat 
      • Honeybell very susceptible
      • Mongi Zekri Ph.d UF/IFAS 5-County Agent
       



          Alternaria Brown Spot on Fruit
          Alternaria is spread by airborne spores. Rain events or sudden changes in relative humidity also favor spore release. Spores are produced on older lesions formed on wilted twigs and mature leaves. Some spores come from fruit lesions but they are not a major inoculum source. Even the leaf contributes to the inoculum. Although the spores are airborne and carried by winds, alternaria brown spot is often spread among groves on nursery stock transported by humans.
          http://idtools.org/id/citrus/diseases/factsheet.php?name=Alternaria

          Symptoms vary from small dark specks to large, black lesions that may turn into corky "pock marks" that can dislodge forming cankers on the fruit surface. Spots are often accompanied by yellowing in the area around the lesions.
          http://www.crec.ifas.ufl.edu/crec_websites/fungal/AlternariaSymptoms.shtml
























          Alternaria brown spot lesions with the typical corky protuberances on Minneola tangelo.
          http://edis.ifas.ufl.edu/ch017
           

















          Light tan pock marks on the peel from where the corky protuberances of Alternaria brown spot lesions have been dislodged.
          http://edis.ifas.ufl.edu/ch017

          Alternaria Brown Spot on Leaves
          Lesions start out as small brown to black spots on young leaves. They expand into irregular blighted areas along leaf veins, accompanied by yellowing of surrounding tissue. Necrosis occurs due to the production of host-specific toxin by the fungus. Lesion size and the degree of necrosis depends on the susceptibility of the infected host.
          http://www.crec.ifas.ufl.edu/crec_websites/fungal/AlternariaSymptoms.shtml



















          Alternaria brown spot lesions on a twig and young leaves. The infection occurred early in the season leading to very large lesions that will likely defoliate this twig.
          http://edis.ifas.ufl.edu/ch017




















          Alternaria brown spot lesions on Minneola tangelo leaves with yellow halos and lesions that follow the veins.
          http://edis.ifas.ufl.edu/ch017


          Additional Information
          Florida Citrus Pest Management Guide: Alternaria Brown Spot PDF
          Alternaria Brown Spot PDF
          Quick Reference Guide to Foliar Fungicides PDF