Abstract
Zero-inflated data from field experiments can be problematic, as these data require the use of specific statistical models during the analysis process. This study utilized the zero-inflated negative binomial (ZINB) model with the log- and logistic-link functions to describe the incidence of plants with Huanglongbing (HLB, caused by Candidatus liberibacter spp.) in commercial citrus orchards in the Northwestern Parana State, Brazil. Each orchard was evaluated at different times. The ZINB model with random effects in both link functions provided the best fit, as the inclusion of these effects accounted for variations between orchards and the numbers of diseased plants. The results of this model show that older plants exhibit a lower probability of acquiring HLB. The application of insecticides on a calendar basis or during new foliage flushes resulted in a three times larger probability of developing HLB compared with applying insecticides only when the vector was detected.
Highlights
Orange (Citrus sinensis) production encompasses the largest acreage of any Citrus species in Brazil
When the zero-inflated negative binomial (ZINB) model was fit to these data, the variables had no influence on the proportion of zeros (Table 1)
The application of insecticides to trees when producing new foliage flushes and the calendar-based approach exhibited a higher incidence of HLB-diseased trees compared with orchards receiving insecticides only when the (D. citri) vector was observed in the orchard, where relative risk (RR) = 4.059 and CI (95%) = (3.025; 5.447), and RR = 3.158 and CI (95%) = (2.193; 4.547), respectively
Summary
Orange (Citrus sinensis) production encompasses the largest acreage of any Citrus species in Brazil. Citrus sinensis was introduced in Brazil during the colonial period, but did not become the largest orange production acreage in the world until the mid-1980s (Couto & Canniatti-Brazaca, 2010). Frozen orange juice, which is largely exported, is one of the most important agricultural commodities in Brazil. International trade could further improve if the current phyto-sanitary issues did not inhibit orchard productivity in Brazil (Paulillo, 2006). The crop is affected by numerous diseases, but only a few are of agricultural importance.
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