Inorganic solar filters incorporated to carnauba wax and incidence of citrus black spot on tangerine
Abstract The objective of this work was to evaluate the effect of zinc (ZnO) and titanium (TiO2) oxides, added to carnauba wax emulsions, on the incidence of citrus black spot (CBS) caused by Phyllosticta citricarpa and, consequently, on tangerine quality. Wax emulsions blended with ZnO or TiO2 were sprayed up to concentrations of 8% on late-season tangerine cultivars. Three experiments were carried out in a randomized complete four-block design, with two control treatments – one with the application of only the carnauba wax emulsion and the other without the application of the emulsion. The spraying of ZnO and TiO2 reduced the incidence of the disease on the harvested fruit; however, the increase in the concentrations of the oxides did not improve CBS control. Two consecutive applications of the oxides reduced the photosynthetic activity of the plants, negatively affecting yield, and caused damage to fruit peel. Tangerines infected artificially with 105 conidia mL-1 of P. citricarpa, before or after the sprayings of the photoprotective films, showed a reduced CBS incidence. The treatments with the application of only carnauba wax do not differ from those with films combined with ZnO and TiO2 regarding the control of CBS incidence. The addition of inorganic oxides to the carnauba films limits the photosynthetic activity and reduces the yield of the plants, besides damaging the visual quality of the tangerines.