Optimization of spray volume for Diaphorina citri Kuwayama (Hemiptera: Liviidae) control in sweet orange groves

The Asian Citrus Psyllid (Diaphorina citri Kuwayama) is a major pest of citrus that vectors Candidatus Liberibacter asiaticus and Candidatus Liberibacter americanus the bacteria associated with Huanglongbing disease. The chemical control, mainly spray application, is the primary tactic against this insect. Thus, this study was carried out to adjust the spray volume used for controlling D. citri. The experiments were conducted in a 4-year old grove of sweet orange ‘Pera’ and spaced at 6.9 x 2.8 meters (518 plants.ha^-1). Dimetoato 500 EC (active ingredient dimethoate) was used as the standard insecticide at 1 L of the commercial product per 1,000 L of water. The study was divided into two phases. In the first, the spray volumes assessed were 1,000, 800, 600 and 500 L.h^-1; in the second, the volumes studied were 1,000, 500, 400 and 300 L.ha^-1. For the second, the volumes 300 and 400 L.ha^-1 were also tested with the rate of a.i. corrected. To assess the efficacy of the treatments, adult psyllids were confined on the tree canopy after application (dry residues). Additionally, in the second trial, spray coverage was measured for each treatment by placing water sensitive paper on the tree canopy. In both experiments, all volumes evaluated were effective in controlling D. citri (mortality≥90%) and there were no significant differences in the percentage of coverage as well. In addition, the spray cost was reduced up to 58% (less water, insecticides and operational cost). Therefore, it is possible to reduce the spray volume currently used for D. citri control keeping effectiveness of this practice, being less expensive and more environmentally friendly.