Coffee, Cacao and Coconut: Diseases of the Tropical Tree Crops

Hemileia vastatrix is an obligate parasite that can only complete its life cycle on coffee plants, and it causes coffee leaf rust. Its page records that it devastated Sri Lanka's coffee industry in the late nineteenth century, helping push British consumers toward tea, and that a resurgence across Latin America and the Caribbean between 2012 and 2014 caused roughly one billion dollars in damage.

Colletotrichum kahawae causes coffee berry disease on Coffea arabica and is described as one of the major factors limiting arabica production across Africa. It makes dark spots and causes green berries to drop early, and because effective control measures are lacking, its page raises concern that it could spread to South America.

Moniliophthora perniciosa causes witches' broom disease of cacao, named for the broom-like malformed shoots it produces. The fungus is thought to have co-evolved with cacao in the Amazon basin. After it reached Bahia state in Brazil in 1989, the state's output fell from about 380,000 to 90,000 metric tons a year, turning Brazil from the world's third largest cacao exporter into a net importer.

Moniliophthora roreri causes frosty pod rot, one of the most serious diseases of cacao in Latin America. Together with witches' broom and black pod rot it forms what its page calls the cacao disease trilogy. It spreads as dry, powdery spores carried by water, wind or the movement of infected pods, and spread is highest in heavy rain.

Phytophthora palmivora is a water mold rather than a true fungus, with a host list that runs from cacao to coconut, mango, citrus, durian, black pepper and rubber. Its page blames it for an estimated ten to twenty percent of global cacao production lost each year. It also causes bud rot in palms and fruit rot of coconut, and its impact was serious enough that commercial black pepper cultivation in Brazil was abandoned.

Erythricium salmonicolor causes pink disease and is commercially significant especially in Brazil. Its hosts include citrus, rubber and cacao trees. The disease produces branch and stem dieback through cankers, which can be recognized by gum exudation and longitudinal splitting of the bark.

Lasiodiplodia theobromae rots and kills back most of the plants it infects, including guava, coconut, papaya and durian, and it causes stem end rot of citrus after harvest. It enters through fresh wounds such as pruning cuts, so its page says management relies on cultural practices like avoiding pruning in wet weather and minimizing wound size.

Cadang-cadang is caused by a viroid and takes its name from a Bicol word meaning dying. First reported on San Miguel Island in the Philippines in 1927 or 1928, it had killed all but 100 of the island's roughly 250,000 palms by 1962. Its page puts the toll at more than 30 million coconut palms since it was identified, with roughly one million killed each year.