從生態學觀點研定柑橘立枯病現行之有效預防策略

Abstract

柑橘類是本省栽培面積最廣，產量最多之重要鮮果。然而由於最嚴重的柑橘立枯病（Li-kubin)，始終找不有效藥劑來防治該病。近年來從探討該病田間發生生態，已獲具體結果。該病在果園之發生與蔓延主要係由媒介昆蟲東方柑橘木蝨（Dinphorina citri）吸取病株之病原而傳播。從1988年設置之試驗園，病區內之柑橘植株經調查木蝨族群週年消長之結果，已獲知木蝨成蟲族群密度在柑橘萌芽期木蝨繁殖極為快速。一般言，春夏芽時期，即三一五月，最適合木蝨之增殖。在病害傳播方面，病區不施藥且有媒介蟲情況下，春夏芽時期亦為重要傳病期。從試驗園之健康苗區與病區之中間種值百香果以隔離，再經加強施藥，經二年之栽培，健康苗區之柑橘苗未被傳染，但病區內種植之健康苗經二年栽培且未施藥，則全部被傳染。另外，在1990年以後的三次試驗，因健康苗區與病區僅隔離五公尺且中間為空地，因此健康苗區雖然有施藥，但部被傳染，然傳染率已有顯著降低。總之，未來本省柑橘立枯病有效預防策略，除加強柑橘萌芽期木蝨族群消長之瞭解與防除外，應選用柑橘無病毒健康苗與砧木來繁殖，以預防病原經由嫁接而傳播，果園內若有發現可疑病株應加強作進一步鑑定，經確定為病株後應剷除。如果，柑橘萌芽期前後注意媒介蟲柑橘木蝨之發生與分佈，萌芽期加強柑橘園之管理與施藥，將可有效預防柑橘立枯病之發生與蔓延。 Citrus likubin is the most important disease in citrus cultivation in Taiwan. At present, it is still not found an effective chemicals to control the disease. From our recent research on the incidence and spread of the disease in relation to the population fluctuation of its vector psyllid, Diaphorina citri. The results clearly indicated that the number of adult psyllids increased from mid-March (mid-Spring), then reached the highest density in late April and early May(early Summer). The high population density lasted about 2 to 3 months (Fig. 1,2) but depends on environmental factors. Generally, psyllids increase in orchard after the new flushes coming out from citrus trees if adult psyllids were survived over winter season in next Spring. To understand the time of likubin transmitted by vector, the results indicated that higher transmission rates occurred in March, April and May from our field experiments. Based on above results, it is clearly that the timing of likubin infection may also be the timing of new sprouts flushing in fields, especially from March to May in one year. However, it is also important that different citrus species planted in different areas, the timing of new sprouts flushing may be somewhat different. Another experiments indicated that intensive insecticide sprayings were effectively prevented the spread of the disease. Therefore, we suggest that intensive spray of insecticides from March, i.e. new sprouts flushing, to May and early eradication of likubin-infected trees be carried out to reduce the spread of likubin in citrus cultivated industry.