Photo 1. Sooty mould on the upper surface of coconut leaflets. Note the twisted leaflet showing a previous scale insect infestation which produced the honeydew on which the sooty mould grew.
A number of sooty mould fungi have been identified in Pacific island countries; e.g., those from Solomon Islands - mostly from living leaves - are as follows: Aithaloderma citri (grapefruit); Capnodium citri (citrus); Capnodium mangiferum (mango); Capnodium sp. (papaya); Chaetasbolisia microglobulosa (chilli); Chaetothyrium setosum (coconut, Xanthosoma taro); Limacinula samoenesis (coconut); Microxiphium spp. (chilli, coconut, oil palm); Trichomerium spp. (coconut, oil palm); Tripospermum fructigenum (Pometia pinnata); Tripospermum gardneri (oil palm, cocoa); Tripospermum sp. (chilli); Triosporiopsis sp. (papaya). Many of these species and others are present in Fiji, Samoa and Tonga.
Other fungal genera recorded are: Antennulariella, Limacinula and Parascorias.
Worldwide. In the sub-tropics and tropics. Sooty moulds are recorded from American Samoa, Australia, Cook Islands, Fiji, Federated States of Micronesia, Kiribati, Marshall Islands, Niue, Papua New Guinea, Samoa, Solomon Islands, Tonga, Tuvalu, and Vanuatu, and are most likely present in all countries of Oceania.
Many plants develop sooty moulds when colonised by insects that produce honeydew, e.g., coconut, guava, mango, soursop and ornamentals, e.g., Frangipani.
There are many fungal species, mostly saprophytes (i.e., non-pathogens) that form sooty mould deposits on trees and shrubs, interfering with the normal function of leaves. Often, their presence is a sign that sap-sucking insects are present (Photo 1). Large populations of insects mean large amounts of honeydew, and dense growths of sooty mould fungi over leaves and stems (Photos 1-4). Often, insect populations increase rapidly, and remain a long time, especially when ants protect them from their natural predators and parasites.
Sooty moulds do not attack plants. The fungi that cause sooty moulds grow on the sugary substances that are produced by insects - mostly, aphids, scale insects, planthoppers, leafhoppers and white flies - as they suck the sap of plants. The secretions are known as "honeydew".
The fungi that grow on honeydew reduce the plants ability to photosynthesise and this may stunt growth, cause leaves to yellow and die early, and may reduce the quality of fruit.
Look for sooty mould on new growth and leaves, since the insects associated with sooty moulds prefer soft tissues.
All the methods used for treating sooty mould are aimed at controlling the insects that secrete the honeydew. Without honeydew, it is unlikely that there would be sooty mould. However, the insects may be protected from their natural predators and parasites by ants, so removing ants should be the first priority, if they are present.
AUTHORS Helen Tsatsia & Grahame Jackson
Photo 3&4 Kohler F, Pellegrin F, Jackson G, McKenzie E (1997) Diseases of cultivated crops in Pacific Island countries. South Pacific Commission. Pirie Printers Pty Limited, Canberra, Australia.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
This fact sheet is a part of the app Pacific Pests and Pathogens
The mobile application is available from the Google Play Store and Apple iTunes.