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Pacific Pests, Pathogens & Weeds - Fact Sheets

Cocoa horsehair blight (005)

Photo 1. Horse hair blight, Marasmius crinis-equi, growing over branches and leaves.

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.

Photo 4. Old leaves of cocoa held together by threads of horse hair blight, Marasmius crinis-equi.

Common Name

Horsehair blight

Scientific Name

Marasmius crinis-equi; also Marasmius equicrinis.

Distribution

Widespread. Asia, Africa, tropical America, the Caribbean, Oceania. It is recorded from Australia, Fiji, Papua New Guinea, Solomon Islands, and Vanuatu.

Hosts

Cocoa is a common host in Pacific islands, but it is also recorded as a disease of tea (Fiji), mango and black pepper.

Symptoms & Life Cycle

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.

Impact

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).

Detection & inspection

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 ).

Management

CULTURAL CONTROL
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

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.

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