Anthracnose of citrus—Collectotrichum gloeosporioides
Anthracnose is a fungus that infects and decays citrus fruit. Most affected are grapefruit and navel and Valencia oranges. Lemons are occasionally infected.
Identification
Fruit disease first appears as tiny black, brown, or red speckling on the rind. Speckles typically develop where water has dripped onto fruit and spores collect there and germinate. Germinating spores produce dark, microscopic hyphae (appressoria, vegetative fungal growths) that appear as dull green to reddish streaks on immature fruit and as blackish to brown streaks on mature rinds. These discolored streaks are called tearstain or tearstreak. Unlike with blackish sooty mold, the anthracnose streaks cannot be scrubbed or washed off.
Infected leaves initially develop yellow tips that turn brown and die. Extensive infection of foliage can cause premature leaf drop that results in a sparse canopy and the dieback of twigs. Dying leaves and twigs become covered with dark fungal spores that spread the pathogen.
Anthracnose often occurs together with Septoria spot. The Septoria fungus and possibly certain environmental conditions can also cause tearstain or tearstreak discoloration of fruit.
Life cycle
Anthracnose generally occurs on stressed trees where it produces spores on old, dead branches, leaves, and twigs. Disease is most common after warm springs with prolonged wet weather and when significant rains occur later in the growing season than normal. Anthracnose spores developing on leaves or wood are moved to fruit by dripping and splashing water. Infections typically occur in the grove, but fruit rot mainly develops after harvest. When the appressoria on fruit germinate, usually after harvest, they penetrate the rind and cause dark, decayed lesions.
Damage
Anthracnose blemishes and decays the rind of citrus fruit. Symptoms of this disease include fruit staining, premature leaf drop, and twig dieback. Infected fruit decays mostly after harvest.
Solutions
During dry weather, prune out and dispose of dead branches and twigs because these are where the fungus overwinters and then spreads to fruit. Anthracnose disease is generally not severe enough to require fungicide application. If anthracnose was an unacceptable problem the previous growing season and the above cultural practices have been employed, disease development may be reduced by thoroughly spraying trees with Bordeaux mixture or copper sulfate fungicide such as copper oxychloride sulfate or tribasic copper sulfate. Make the application after the first rain in the fall.
Adapted from Integrated Pest Management for Citrus and Pest Management Guidelines: Citrus, University of California Statewide Integrated Pest Management Program (UC IPM). For more information see Pest Notes: Anthracnose. |
