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ANTANANARIVO, March 30 (Reuters) - Aid workers began using pirogues on Friday to ferry food to thousands of flood-stricken Malagasy people in remote areas of Madagascar, which is struggling with the aftermath of cyclones and tropical storms.

"Over the last few months, Madagascar has been hit by the worst series of cyclones in many years bringing severe flooding ... and directly affecting almost 500,000 people," a United Nations statement said on Friday.

An estimated 100,000 people have been displaced on the enormous Indian Ocean island, the statement added.

The storms have also wiped out an estimated 80 percent of vanilla production on Madagascar -- the world's largest supplier of vanilla -- and in the worst-hit south-eastern regions destroyed up to 90 percent of the rice harvest.

"The government is making efforts to repair infrastructure but the damage to roads and bridges will continue to constrain the response," the United Nations said, adding that some areas had been under water for eight weeks.

A spokesman for Care International, Alexis Poniatowski, said his organisation had begun using wooden boats to deliver food aid to some 20,000 people in north-east Madagascar where Cyclone Indlala struck a month ago.

"Pirogues are the only way to reach people in isolated villages," he said.

"The land and roads have been totally flooded," he said, adding that the furthest villages were five hours away by boat.

Last month, the Malagasy government appealed for $242 million to help cope with multiple natural disasters, including also a drought in the south which affected 582,000 people.

The world's fourth largest island, located off the south-east coast of Africa, could be hit by further storms in the current cyclone season, the U.N. statement said, listing damage to food stocks, schools, health infrastructure, and water points.

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