OCCURRENCE AND INGROVE DISTRIBUTION OF CITRUS HUANGLONGBING IN NORTH CENTRAL FLORIDA
W. Shen, S.E. Halbert, E. Dickstein, K.L. Manjunath, M.M. Shimwela, A.H.C. van Bruggen
Citrus huanglongbing (HLB) has affected the citrus industry severely since it was first observed in south Florida in 2005. No published information is available on occurrence and in- grove distribution of HLB and its psyllid vector Diaphorina citri in north central Florida. D. citri and citrus leaf samples were collected from one organic and two conventional groves in Citra, FL, and from individual trees on the University of Florida (UF) campus in Gainesville to be tested for Candidatus Liberibacter asiaticus (Las) using qPCR. Las-positive D. citri samples were detected in Gainesville in 2007, and Las-positive trees were first found on the UF campus in October 2011. Las positive D. citri samples were obtained from symptomless trees in the organic grove in 2006 and 2007, and Las was first detected in leaf samples from asymptomatic orange trees in spring 2012. Trees in the conventional groves were Las-negative. HLB symptoms were first found in autumn 2012 in the organic grove and to a lesser extent in one conventional grove. HLB incidence was high along the northeastern edge of the groves. Semivariograms for within- row and across-row HLB spread were constructed using Las Ct values and tree distances. Monomolecular models were fit to the semivariance data. The range (=zone of influence) of HLB-infected trees was greater within rows (20 m) than across rows (13 m), suggesting that D. citri transmits HLB more readily within than across rows. Infection of conventional trees was probably delayed due to surrounding windbreaks. There was no relation between nutrient contents and HLB development.