Cocoa yields are mushrooming--downward.

Hoping to preserve the world's chocolate output, scientists have begun fighting fire with fire, so to speak--or in this case, fungus with fungus.

Until about 5 years ago, Brazil was the world's second-leading exporter of cacao, the bean from which cocoa and chocolate are made. Since then, Brazilian cacao yields have nose-dived to about 25 percent of their former level. The reason for the drop is that plantations have suffered an epidemic of attacks by the witches' broom mushroom, Crinipellis perniciosa. The blight's name comes from the clustered strawlike twigs that develop on infected branches. More importantly, the fungus destroys cocao beans.

Scientists observed that some Crinipellis specimens in the Amazon were infected with a debilitating bright-green, fuzzy fungus called Trichoderma viride. They began investigating this infection as a potential biological control. Trichoderma can kill Crinipellis before it sprouts into a spore-forming, pink, fan-shaped mushroom, explains Robert D. Lumsden of the U.S. Agricultural Research Service in Beltsville, Md. He's part of an international team that has begun cultivating this Trichoderma species.

Last fall, the researchers offered cacao growers Trichoderma spores in the first experimental sprays for treating blighted trees. "There is already some indication that it's cutting back on the incidence of witches' broom," Lumsden says. However, he told SCIENCE NEWS, growers shouldn't expect cacao yields to improve dramatically--at least within the next few years.