Risk analysis of introduction and spread of huanglongbing in citrus groves in Rio Grande do Sul, Brazil

Huanglongbing (HLB), the most damaging disease of the citrus industry, is present in the Brazilian states of Sao Paulo, Minas Gerais and Parana. The risks of introduction and spread of this A1 quarantine pest in citrus groves of the Rio Grande do Sul (RS) state were assessed based on a structured questionnaire composed of 27 questions applied to 163 growers in 35 municipalities. The locations were defined according to the economic relevance of citriculture, and the sample size (number of interviewed farmers) was proportional to the cultivated area in each municipality. A multi-criteria method was used to prioritize and assign weights to specific criteria associated with the different risks. Each farm was assigned to one of the four risk categories: low (0 to 0.25), medium (0.25 to 0.50), high (0.50 to 0.75) and very high (0.75 to 1.0). The estimated risks of HLB introduction and spread in RS were mostly medium to high across the regions and farms within regions. Two factors, the presence of HLB in neighbor countries and citrus fruit transport from other regions mostly accounted for the risk of introduction of HLB into RS. Following an eventual introduction, the lack of knowledge about this pathosystem and the little or no use of insecticides were identified as the main contributors of disease spread within the state.