Abstract
Citrus greening (CG), also called huanglongbing, was found on Tokunoshima, Okinoerabu and Yoron islands of Kagoshima in southern Japan in 2002. Because inter- and intra-island transportation of citrus trees has been banned since April 2007, new CG infections that developed after the ban can be attributed to transmission by the vector, Diaphorina citri. Since the first record of the disease on the islands, disease spread on these islands has been studied at 10,176 sites on a total of 63,295 trees. Using data from before April 2011, CG infection pressure was evaluated by analyzing the spatiotemporal distribution of CG on the infected trees in the studied areas. Newly confirmed area with infected trees amounted to 75% on Tokunoshima within 21 m, Okinoerabu within 90 m and Yoron within 241 m of areas with infected trees confirmed in the past 2 years. Areas were classified into three infection pressure ranks (IPRs; low to high): IPR-1, ≤ 0.5; IPR-2, >0.5 to 2.0; IPR-3, >2.0. The frequencies of uninfected/infected trees in each rank during the 2 years after April 2007 were calculated and compared between infection ranks. Odds ratios indicated that the infection risk of trees in IPR-2 was seven times higher than in IPR-1 and six times higher in IPR-3 than in IPR-2. For the predicted risk, monitoring of CG is discussed.
