Could the day come when the only chocolate bars are in museums? South America's cacao growers are warily watching the spread of witches'-broom fungus, which infects seed pods and sends out evil-looking orange shoots. It has slashed Brazil’s cocoa production by more than 25 percent in the past five years.
Crowded cacao plantations encourage the rapid spread of the witches'-broom fungus, and fungicides don't work well amid the heavy rains of the tropics. Robert Lumsden of the U.S. Agricultural Research Service in Beltsville, Maryland, is leading an effort to fight fungus with fungus—Trichoderma, which attacks witches'-broom and other cacao pests. Field trials in Peru and Brazil show that Trichoderma fungi are effective and harmless to the trees. But the genetic uniformity of commercial cacao groves still leaves them vulnerable to future attacks.