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Citrus Scab (Elsinoe fawcettii): A Review

K Gopal, B Govindarajulu, K T V Ramana, Ch S Kishore Kumar, V Gopi, T Gouri Sankar, L Mukunda Lakshmi, T Naga Lakshmi, and G Sarada

Elsinoë fawcettii Bitancourt and Jenkins is the causal agent of citrus scab. It is widely distributed, occurring in many citrus growing areas in the world where rainfall conditions are conducive for infection. It affects all varieties of citrus, resulting in serious fruit blemishes and e conomic losses world - wide. Conidia are produced from the imperfect stage of the fungus, Sphaceloma fawcettii Jenkins, and serve as the primary source for inoculation in the field. E. australis causing sweet orange scab differs from E. fawcettii in host ran ge and is limited to southern areas in South America. E. fawcettii rarely causes lesions on sweet orange, whereas E. australis attacks all sweet oranges as well as some tangerines and their hybrids. Unlike E. fawcettii that induces lesions on all parts of citrus, E. australis appears to affect only fruit. In addition, E. australis can be distinguished from E. fawcettii based on the sizes of ascospores (12 - 20 x 15 - 30 μm in E. australis ). Furthermore, E. australis does no t produce spindle - shaped conidia in scab lesions that are often associated with E. fawcettii. Elsinoë spp. produces two kinds of conidia: hyaline conidia and spindle conidia. Hyaline conidia of Elsinoë spp. are one celled, elliptical, and 2 - 4 x 4 - 8 μm and are the primary source for inoculation. Spores are produced on diseased tissue after only one to two hours of wetting. Spores are then dispersed by water splash to healthy young leaves and twigs where the infection takes place. Three to four hours of wetne ss is required for infection. Citrus is most susceptible at fruit developing stage. Citrus scab affects a variety of citrus species while Sweet orange scab affects primarily orange and mandarines. The best management measure is avoiding entry of contaminat ed material. Once established, the disease can only be managed by two chemical sprays, the first one when 25 % of the flowers are open, followed by a second spray 7 - 10 days after. Copper - based fungicides, benomyl, thiram, captafol and chlorothalonil, carbe ndazim, thiophanate methyl, trifloxystrobin, ferbam, azoxystrobin, trifloxystrobin, pyraclostrobin plus oil are the best chemicals for scab control.