Photo 2. Pink disease of cocoa, Phanerochaete salmonicolor, has killed the branches, but the leaves still remain attached. (Pink disease is present on the central branch where it shows as a lighter colour.)
Pink disease of cocoa
Erythricum salmonicolor; also known by older names, Phanerochaete salmonicolor, and Corticium salmonicolor.
Worldwide. It is recorded from all countries growing cocoa: Fiji, Papua New Guinea, Samoa, Solomon Islands, Tonga, and Vanuatu, but also present elsewhere, e.g., Cook Islands on other trees.
Cocoa is a major host, but it occurs on Agathis (kauri), citrus, coffee, Cordia, Hibiscus, mango, and many other trees.
The fungus causes dieback on woody trees and shrubs. Often the disease starts from near where a branch originates.
The first sign of the disease is white threads of the fungus over the bark; they look like cobwebs. White pustules appear through cracks and through natural openings in the bark. Later, the fungus forms a pink crust which produces spores (Photos 1&2). Later still, but only occasionally, the colour fades and orange-red pustules, which contain another type of spore, are seen.
Cankers often form; the fungus penetrates and kills the bark, cracks appear, the crust becomes grey and sunken, and gum may be present (Photo 3). The leaves die on the infected branches, but remain attached.
When it is too dry and unfavourable for growth, the fungus remains alive in the branch and trunk cankers.
Spores of the fungus are spread by wind and rain. They need water to germinate, and then they can infect through healthy bark.
The disease causes a branch dieback, and occasionally death of the tree when infections are at the main fork or "jorquette". Often, within a plantation, patches of infected trees occur as the disease spreads. If management is poor, and weather conditions encourage the disease, losses can be high, but usually the disease is of minor importance. Trees between 2 and 6 years old are said to be most severely affected.
Look for the pink crust on branches and trunk. The fungus is often seen at the jorquette. Regular surveys to detect infections are very important. Often, the first sign of the disease is the sudden death of a branch, with the brown leaves hanging down, but still attached.
The health of the trees is important in preventing outbreaks of this disease. If trees are stressed, because they are too close or growing in soils with poor nutrition, then they may be more susceptible to infection.
Copper fungicides are useful if applied as a paste. Prune the branches and apply the paste to the cut ends and along the remaining parts. Apply to infections at the jorquette.
AUTHORS Helen Tsatsia & Grahame Jackson
Photo 3 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.
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