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Huanglongbing spatial pattern in Sao Paulo state, Brazil

Kelly Pazolini: University of São Paulo

<div>Huanglongbing (HLB) is considered the most devastating disease of citrus worldwide, and is known to occur in many citrus growing regions worldwide, including Brazil, the USA and China. Quantifying the spatial nature of spread of the causative bacterium can be a key to understanding the epidemiology of the pathogen, which can then be used to inform and improve control measurements. The aim of this study was to determine the spatial pattern of HLB in plots under strict management in São Paulo state, Brazil. For this, modified Ripley’s K-function, ordinary runs analyses and kernel density estimation were performed on a total of 81 annual “snapshots” of the spatial distribution of infection in 22 commercial citrus plots (each composed of approximately 13,840 trees over 24.9 ha) between 2013 and 2017. These plots were managed with HLB control based on, at least, four inspections per year for detection and rouging of symptomatic trees and regular insecticide sprays. Trees rouging incidence and vector detection on yellow stick cards on the 22 plots ranged from 0.7 to 23.4% and 0 to 1.9 adults/yellow stick card/assessment, respectively. Results of the modified Ripley’s K and ordinary runs analyses found no evidence of aggregation on the 22 plots studied, suggesting that primary spread from surrounding areas predominates. This finding was also supported by kernel density estimation, which found the highest density of suspected infected trees around the plot periphery.</div>