Epidemiological and economic model to estimate the optimal edge width of citrus block to be weekly sprayed with insecticide for huanglongbing management

ABSTRACT A modeling approach was implemented to assist growers in estimating the most economical edge width to be sprayed weekly (EWSW) with insecticides for the management of the Asian citrus psyllid (ACP) Diaphorina citri, vector of the causal agent of huanglongbing (HLB), in the periphery of sweet orange farms. The model was developed based on epidemiological and economic data. Different scenarios of EWSW with fortnightly sprays in the rest of the block were compared. Four regions within the São Paulo/Triângulo Mineiro (SPTM) citrus belt were selected for analysis: Frutal, located in Triângulo Mineiro (TM), as well as the municipalities of Bebedouro, situated in the north (NO), Araraquara, located in the center (CE), and Avaré, situated in the south (SO) of the state of São Paulo (SP), Brazil. The model inputs used to estimate the number of HLB-symptomatic trees in each region included the number of immigrating ACPs, percentage of ACPs infected with ‘Candidatus Liberibacter asiaticus’ (CLas), infection efficiency, and insecticide spray efficacy. Four economic simulations (panels) were performed, considering general or specific regional costs and yields. Accumulated costs, which encompassed expenses with insecticide spray, removal of infected trees, and reset, and benefits, which includes revenue received from the remaining bearing trees, were considered according to tree age (3-15 years old) in order to calculate the net present value (NPV). The highest NPV was standardized as 100, and this index was used to compare scenarios and panels. Across all scenarios and panels, the most economical EWSW remained consistent, ranging from 1 (in the first row), 217, 189, and 497 m (across the entire plot) at TM, NO, CE, and SO, respectively. This indicates that while costs and yields can alter the NPV, they do not alter the optimal EWSW.