Insecticidal control of Diaphorina citri: Effect on titer of Cadidatus. Liberibacter asiaticus and yield of ‘Valencia’ oranges in Florida

The relationship among citrus plants, Diaphorina citri Kuwayama, and Candidatus Liberibacter asiaticus is one of the most economically important in citrus groves in Florida and other citrus producing regions of the world. The Asian citrus psyllid, D. citri, is the vector of Can. Liberibacter asiaticus, a phloem limited bacterium considered the putative causal agent of Huanglongbing (HLB), the most devastating citrus disease worldwide. A 12-acre block of a commercial orange grove located in Collier Co., FL was selected to evaluate the effect of vector management on bacterial titer and fruit yield. The block was divided into 16 plots organized in a randomized block design with eight replicates and two treatments. The first treatment remained free of insecticides and the vector was allowed to thrive. In the second treatment, the psyllid population was monitored every 2 weeks and insecticide was sprayed when insect populations surpassed the nominal threshold of 0.5 psyllids per tap sample. To assess the titer values, we selected symptomatic branches on every fifth tree in every row for real-time PCR analysis every four months. Initially CT values and the percentage of PCR positive trees did not differ between treatments. In the last two years, CT values have dropped and most trees eventually tested positive. CT values from insecticide-treated trees became significantly higher, indicating lower bacterial titers, compared with untreated plots. Treated trees had significantly higher yields than the untreated trees. These results indicate that mitigation of vector pressure with insecticide decreased alleviated bacterial titer over time and positively affected yield despite the same incidence of HLB.