HLB progress and yield sustainability in mature sweet orange orchards treated with nutritional and elicitor products

Although the implementation of area-wide inoculum reduction and Asian citrus psyllid (ACP) control are decisive in controlling Huanglongbing (HLB) epidemics, growers continue looking for enhanced nutritional and/or resistance inducer (ENRI) treatments to mitigate yield damage in HLB-affected trees. Therefore, an experiment was set up in an 8-year-old sweet orange orchard to evaluate the effects of the foliar application of nutrients, phosphite, and salicylate sprayed four to five times per year during flushing periods. The trial had eight treatments in four randomized blocks. HLB incidence and yield were assessed from December 2010 to January 2017. HLB-symptomatic trees with less than 5% HLB severity were selected from each plot in the first (Group 1), second (Group 2), and third years (Group 3) after the beginning of treatments to assess the frequency of trees with different HLB symptoms and micronutrient deficiencies, HLB severity, and fruit yield until January 2017. Twenty asymptomatic trees from each plot were also harvested for comparison each year. ENRI treatments did not reduce the progress of HLB incidence in the plots or the HLB severity progress or frequency of HLB symptoms in the selected trees. ENRI treatments did not improve the yield of symptomatic trees compared to asymptomatic trees. Hence, in a scenario without HLB-symptomatic tree removal in mature orchards, disease severity progress and yield reduction in HLB-affected trees remained regardless of ENRI treatment.