Management of huanglongbing (HLB) by an intensive vector and disease control in the surroundings of the orchard, in addition to planting HLB-free trees in Okinawa, Japan

Abstract

Citrus greening disease, huanglongbing (HLB), is one of the most destructive citrus diseases worldwide. The causal agent, Candidatus Liberibacter asiaticus (Las), is transmitted by the Asian citrus psyllid, Diaphorina citri (Hemiptera: Liviidae). In Okinawa, in the beginning of 2000, HLB was widespread. Local control and planting of HLB-free trees were considered necessary measures to manage HLB. In 2006, 25 HLB-free trees were planted at an experimental field in Okinawa. Then, insecticides were sprayed in the experimental field according to the spray calendar (during the experimental period: imidacloprid 20%, thiamethoxam 10%, dinotefuran 20%, and clothianidin 16%; each application rate was 0.1 L/m 2 ). In addition, "local control," that is, insecticide spraying [fenitrothion 50% twice a year from 2006 to 2008, mineral oil 97% once, and methidathion 40% (June-July) once after 2008; each application rate was 0.1 L/m 2 ] and removal of HLB-positive trees in the residential area, were continued. Until 2010, psyllids were very few, and none of the 25 planted trees were infected with HLB in the experimental field. Even in 2011, only 3 of the 25 trees were infected, indicating that the HLB infection rate was low when greening-free trees were initially planted and local control (pest control and removal of infected trees in the residential area) was effective at an early stage of cultivation. This result suggests that even in Japan, local control and planting HLB-free trees are effective in managing HLB.