Tree age and cultivar-oriented use of mineral oil added to fungicide tank mixture for the control of citrus black spot in sweet orange orchards.

Abstract

Mineral oil added to fungicide spray mixtures has been a frequently used strategy to control citrus black spot (CBS) worldwide. Although mineral oil may increase the efficacy of control, its use represents around 15% of the costs of a CBS spray program. This study aimed to assess the performance of different proportions of mineral oil added to a fungicide tank mixture for CBS control in young (less than 10 years old) and old (more than 12 years old) sweet orange orchards of early ('Hamlin'), mid-season ('Pera') and late-maturing ('Valencia') cultivars in São Paulo state, Brazil. The efficacy of 0.15%, 0.20% or 0.25% mineral oil added to a fungicide spray mixture was determined by assessing CBS incidence, severity and fruit drop in six orchards over two seasons. Fungicide programs with or without oil were effective in reducing 100% CBS symptom expression in both young and old 'Hamlin' orchards and in the young 'Pera' orchard. The lowest mineral oil rate tested (0.15%) showed a reduction in CBS intensity of around 90%, similar to the highest rate tested in the old 'Pera' orchard. The highest cost-benefit program to control CBS in the old 'Valencia' orchard was obtained with the mineral oil rate of 0.25%, commonly used in the São Paulo citrus belt, which reduced CBS severity by up to 97%. This study demonstrated that mineral oil rates for CBS control can be adjusted according to tree age and cultivar. These findings contribute to the establishment of more sustainable citrus production by reducing spray costs while maintaining the efficacy of CBS control. © 2021 Society of Chemical Industry.