Spatiotemporal spread of huanglongbing in commercial citrus orchards of Minas Gerais, Brazil

Abstract

The spatiotemporal spread of citrus huanglongbing (HLB, ex greening) in Minas Gerais (MG) state, Brazil, was analyzed since its first detection in 2005. Data on the amount of eradicated plants per orchard were gathered from the georeferenced database of the state’s official HLB monitoring program. In total, 1487 orchards (118 municipalities) have been inspected yearly up to 2018. Overall, 57.2% (64.4% of the municipalities) of the orchards were affected by HLB and a total of 459,254 plants, mainly mandarins (62.7%) and sweet oranges (35.6%), and very few lemon and acid lime (1.7%), have been eradicated. The percent of HLB-affected orchards was variable in three scenarios of citrus varieties and citrus-growing regions: 20% of sweet orange orchards in the Triângulo Mineiro (TM) region and 64.8% in the South of Minas (SM) region, and 80% of mandarins produced in the SM and 40.4% in the Central regions. The numbers of eradications were generally higher in mandarins in the SM than in sweet oranges in the TM because of the large orchard size, better management, and more recent introduction of the disease. HLB spread faster among orchards in the SM and Central regions due to a lack of HLB-oriented management, small size, and proximity between each other. The disease has spread 45.9 km/year and 25.7 km/year on average in the TM and Central/SM, respectively. The HLB-affected orchards were spatially aggregated in mandarin orchards in the SM, which was not evident in sweet oranges growing the TM and SM. Research and extension resources shall be mobilized to help citrus farmers of the SM and Central regions to extend as much as possible the feasibility of the production and prevent further spread among and within mandarin orchards in Central MG. These results can be of value to further improve risk assessment of HLB spread in other regions that share similarities with those in MG state.