Pacific Pests, Pathogens, Weeds & Pesticides
Cocoa horsehair blight (005)
Photo 2. Black threads of horse hair blight, Marasmius crinis-equi, growing along a branch and then from the branch over the surface of a leaf.
Photo 3. Old leaves of cocoa held in place by threads of horse hair blight, Marasmius crinis-equi, giving the impression that they have been killed by the fungus.
Marasmius crinis-equi; also Marasmius equicrinis.
Asia, Africa, tropical America, the Caribbean, Oceania. It is recorded from Australia, Fiji, Papua New Guinea, Solomon Islands, and Vanuatu.
Cocoa is a common host in Pacific islands, but it is also recorded as a disease of tea (Fiji), mango and black pepper.
The threads are smooth brown to black resembling horsehair, about one tenth of a mm in diameter (Photos 1&2). The threads travel along branches and over leaves. The leaves break from the branches and remain suspended in place by the horsehair threads.
The fungus is often thought to cause a disease, but it does not. The fungus grows over healthy leaves, but does not infect them. However, when the leaves break naturally from the stems, they are held in place by strands of the fungus, which gives the appearance that the fungus has killed them (Photos 3&4).
Look for thin black threads along branches and over leaves. Look for leaves that are dead but suspended in place by horsehair threads. Compare with other black thread blights, e.g., Pellicularia koleroga (see Fact Sheet no. 199 ).
This fungus is not thought to be pathogenic on cocoa so control measures are not warranted. Whether or not it is pathogenic on other hosts is uncertain.
AUTHORS Helen Tsatsia & Grahame Jackson
Information from CABI (2020) Marasmius crinis-equi (horse hair blight). Crop Protection Compendium. (https://www.cabi.org/cpc/datasheet/34923).
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.