Citrus pests in Japan
In Japan, the main pests and diseases of Citrus which can cause significant losses are Scirtothrips dorsalis (EU Annex II/A1), citrus red mite (Panonychus citri), Diaporthe citri, Xanthomonas campestris pv. citri (EPPO A1 quarantine pest), Satsuma dwarf virus (EU Annex II/A1) and post-harvest diseases.
Scirtothrips dorsalis is the most frequent pest in Japanese Citrus groves, although it became an important pest only in recent years. All cultivars can be attacked, but navel oranges are particularly susceptible. This pest feeds on young plant tissues (young leaves, stems and fruits), and the most significant damage is caused from June to October. Attacked fruits show greyish or silvery scars on the peel. The thrips cannot develop below 9 øC, and it takes approximately 1 month in the cool season and 13-15 days in summer to complete one generation. When climatic conditions are favourable, up to 8 generations per year can be observed. In Japan, normally four insecticide treatments are recommended during the growing season (e.g. acephate or dimethoate + fenvalerate).
Satsuma dwarf virus has been observed in many citrus groves in the major citrus-growing areas of Japan. Symptoms appear on the leaves when new shoots began to grow in spring. Symptoms are characterized by leaf deformation (boat- or spoon-shaped), shortening of internodes, and fruits of severely affected trees are small with thickened peel and insufficient sweetness. Latent infection is observed in many citrus cultivars. The virus is mainly transmitted by propagation material, but other mechanisms of natural transmission are not known, although the role of a soilborne vector is suspected. In order to prevent the spread of the disease, virus-free planting material should be used, and some research is being carried out on the possible use of mild strains.
Xanthomonas campestris pv. citri is also a serious disease, especially as some newly selected cultivars of Satsuma mandarin may be more susceptible to citrus canker. In Japan, treatments with copper compounds (Bordeaux mixture, cupric hydroxide, copper sulfate) or antibiotics are applied in spring and autumn.
Sources
Furuhashi, K.; Serizawa, S. (1994) Present situation in the control of citrus insect pests and diseases in Japan.
Agrochemicals Japan, no. 64, 8-11.