The occurring factors and control efficacy of citrus fields lightly damaged with citrus melanose caused by D. citri. in the eastern district of Shizuoka prefecture
1998
Masui, H. (Shizuoka-ken. Citrus Experiment Station, Shimizu (Japan)) | Nomura, A. | Serizawa, S.
In 1995 and 1996, the occurrence of citrus melanose caused by Diaporthe citri was assessed. The damage of disease was significantly lower in Nisiura district of eastern Sizuoka prefecture than in central area, despite of fewer (twice compared to 4 times) application of fungicide. We confirmed that the population of a spore of D. citri formed on dead twigs was lower in Nisiura area than in central area. At the same time, considerable number of conidia of Colletotrichum sp. was observed on the samples from Nisiura. The amount of dead twigs of the light infection field in Nisiura was unexpectedly higher than that of usual infection fields in the central area, and was suspected not to correlate with the disease severity. Detached healthy twigs were held amongst the citrus trees in the fields and the population change of fungal spores were observed throughout a year. In Nisiura district, the formation of alpha of D. citri was constantly lower and the conidia of Colletotrichum sp. was also constantly isolated in Nisiura district. Death of the detached twigs went more slowly in Nisiura fields, compared to the fields of central area. The slow death of twigs was suspected to lead to smaller formation of D. citri spores and consequently to low infection of citrus trees
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