An incurable crop disease has spread widely in Madagascar's vanilla-producing region, government scientists said Monday. The scientists' initial assessment released Monday said the world's main vanilla exporter needs to radically change farming methods to fight the disease, carried by an underground fungus.

Most of Madagascar's vanilla is exported to the United States, where it is used in candy, soft drinks and ice cream.

"The situation is critical," Malagasy agronomic research chief Simeon Rakotomamonjy told The Associated Press. "The disease now affects 80 percent of plantations around Sambava and Andapa," two of Madagascar's three main centers of vanilla production.

Surveys in the more isolated Antalaha region so far reveal only a trace of the fungus.

Fungus spores attack a vanilla plant at the root, and a black rot spreads upward, often killing pods before they reach maturity. The disease is known for the moment only by its local name, bekorontsana, which means "falls to the ground often," said plant specialist Alain Paul Andrianaivo.

Researchers propose a wholesale replanting of disease-prone species with a vanilla hybrid that, laboratory tests suggest, is fungus-resistant.

If new plants are the answer, the government will have to help, said Charles Gabriel, a farmer in the affected region.

"For the moment I have not got the money to buy new plants," said Gabriel, who farms two fields he inherited from his parents. "I would also need to see that it works before I begin planting."

Monday's report did not address how fighting the disease would be funded.

High prices on the world vanilla market contributed to a surge in unregulated planting 10 years ago, researchers say. The result has been poorly irrigated fields of plants set too close together, helping the disease spread rapidly now.