Assessment of Sooty Mould Incidence on Citrus (Citrus sinensis) Orchards in Oyo State, South West Nigeria

Sooty mould, a group of superficial fungal growths developing on honeydew secretions from phloem-feeding insects, has been associated with deteriorating citrus (Citrus sinensis) leaf health and fruit appearance in orchards across Oyo State. While sooty mould fungi are non-parasitic, their accumulation on leaf surfaces impairs photosynthetic efficiency and significantly reduces fruit marketability. This study assessed sooty mould incidence and its association with insect vector populations in sweet orange orchards in three local government areas of Oyo State. Field surveys conducted between January and June 2023 included disease rating of 50 orchards and concurrent sampling of scale insects and whiteflies on infested plants. Laboratory examination identified Capnodium citri and Meliola spp. as the primary sooty mould fungi colonising citrus foliage and fruit surfaces. Sooty mould incidence correlated positively with the density of Aonidiella aurantii and Dialeurodes citri populations recorded on survey trees. Orchards with closed canopies and no pruning history consistently recorded the highest mould ratings. Most farmers were unaware of the connection between mould development and insect management, focusing remediation efforts exclusively on fungicide applications without addressing insect populations. The study recommends integration of vector control programmes with canopy management practices to reduce sooty mould pressure in Oyo State citrus orchards. Keywords: citrus, sooty mould, Capnodium citri, scale insects, Oyo State.