Tree hygiene for effective management of citrus black spot in Australian mandarin orchards

Citrus black spot (CBS), caused by Phyllosticta citricarpa (McAlpine) Aa, is a major concern for Australian citrus production, especially in export-focused regions.
Four field trials were conducted from 2022 to 2024 in mandarin (Citrus reticulata) orchards in sub-tropical regions of Queensland to evaluate the impact of pruning-debris (cut branches and twigs left in the canopy after commercial pruning) in tree canopies and altered fungicide spray programs on CBS management.
In field trial (FT) 1, adding pruning-debris to the canopy markedly increased CBS incidence in all but one treatment, irrespective of fungicide application, highlighting the significant role of pruning-debris as an inoculum source.
Adding pruning debris did not increase CBS incidence when regular copper fungicide sprays were applied throughout the entire early season (August-October), also highlighting the importance of effective inoculum control when fruit are most susceptible to CBS infection.
In FT-2 and -3, removing pruning-debris reduced CBS incidence by 18 and 7%, respectively.
In FT-4, early season copper fungicide applications (fortnightly or fortnightly then monthly) significantly reduced CBS-diseased fruit compared with monthly and or untreated fungicide application regimes.
These findings suggest that conidia in the canopy could be a primary infection source, rather than spores from leaf litter.
This study also highlights that leaf litter management is less critical, with overall tree hygiene, including timely pruning-debris removal, playing a dominant role in effective CBS control.

XV International Citrus Congress

T. Thangavel, M.W. Smith, A. Miles, B. Gallagher, M. Wallis, T. Cooke, E. Martin, T. Peressini, M. Reid, K. Bransgrove, L. Coates

P. citricarpa, pruning-debris, inoculum source

https://doi.org/10.17660/ActaHortic.2026.1448.64