By Jeremy McDermott BBC correspondent in Colombia

Farmers say spraying kills all crops and ruins their livelihood

Drug cultivation in Colombia has fallen by more than 30% so far this year, according to a United Nations report.

The Colombian Government is heralding the findings as proof that its massive aerial eradication programme is paying off.

But critics claim the scheme is not eradicating drug fields, simply displacing them, and fear it will damage the Amazon's delicate eco-system.

While crops are down in Colombia, they are on the increase in Peru and Bolivia - and, tellingly, cocaine supply to the United States has not been interrupted and prices stay the same.

Military aid

The news that drug cultivation in Colombia has fallen by 32% comes amid concern over its controversial crop-spraying programme.

The scheme is financed by the US and is Washington's principle condition for continuing military aid.

But peasants and human rights groups oppose the spraying of toxic chemicals over drug fields, many of which are in the vulnerable Amazonian rainforest.

The glyphosate chemicals, which are sprayed from planes kill all plant life, not just drug crops, and leave peasants destitute.

Critics allege the spraying simply feeds displacement and leads to more virgin rainforest being cut down, and that manual eradication is the only way forward.

There are those that dispute the UN figures. Large industrial drug plantations have disappeared in most parts of the country. But smaller fields, too tiny to attract the notice of spray planes and perhaps even the satellite imagery, proliferate.