Two US-made Black Hawk gunships dot the sky as Edelberto Narvaez strips leaves from bushes in the jungle-covered mountains of Colombia's Putumayo province.
"That means the crop sprayers are coming," says Narvaez, who has 4ha planted with the bushes that yield the raw material for cocaine.
The US has spent more than $4 billion (R25 billion) in six years supplying crop-spraying planes, helicopter escorts, arms and advisers to help Colombia combat the production of cocaine, marijuana and heroin by farmers like Narvaez.
Plan Colombia, as the programme is known, is taking a toll on coca growers in Putumayo, according to UN estimates. John Walters, the director of the White House's office of national drug control policy, says the plan is saving lives in the US and in Colombia. Yet farmers there are learning to adapt to fumigation and production is rising in Peru and Bolivia.
Colombian vice-president Francisco Santos says that while progress has been made, results have fallen short of the target. "We have been very aggressive against drug traffickers and drugs, but we may have underestimated their ability," says Santos.
From 2000 to 2004, the area under coca cultivation in Colombia was halved to 80 000ha as bushes were destroyed and farmers took up Plan Colombia grants to switch to other crops, according to the latest UN figures. In the same period, the area in Bolivia increased to 27 700ha from 14 600ha, and in Peru to 50 300ha from 43 400ha, the UN says.
In southern Colombia's Putumayo, the area planted with coca dropped to 4 386ha by 2004 from 66 022ha in 2000, when the province accounted for half the nation's coca output.
The stakes for both the US and Colombia are substantial.
Colombia intends to destroy a drug trade that has financed guerrillas who for four decades have waged war on the government and made Colombia one of the world's most violent countries in terms of kidnappings, murders and terrorist attacks.
For its part, the US seeks to reduce supplies of drugs on its streets that contribute to crime and addiction.
Walters says the US aid is paying off. A 19 percent increase in the street price and a 15 percent decline in its purity between February and September last year are evidence that supplies have contracted, he says. The US Congress has approved about $600 million for Plan Colombia this year.
Sandro Calvani, the head of the UN Office for Drug Control and Crime Prevention in Colombia, says switching to legitimate crops isn't easy in places such as Putumayo, where the Revolutionary Armed Forces of Colombia and paramilitary groups fight for control of the drug trade and kill and threaten farmers who want to give up coca growing.
Calvani says those who do switch to other crops face difficulties, including the challenge of transporting their produce to market over makeshift bridges and along the province's few, poorly maintained roads.
Adding to their hardships, Putumayo's 379 000 residents spent 34 days without power in 2005 after guerrillas blew up electricity pylons. Villagers are regularly forced to leave their homes as bombs explode around them and travellers are often forced from their cars by armed troops searching for drugs and weapons.
"It is critically dependent on the commitment and perseverance of a difficult programme to not simply attack the drug threat but to change the culture that the druggers have worked 30 years to create: corruption, weak government and of a sense of hopelessness," says William Wood, the US ambassador to Colombia.
Maria Ruth Diaz gave up coca production after her 50ha plantation was sprayed two years ago. Now she raises pigs on the outskirts of Orito. She and her family of 11 receive about 600 000 pesos ($263) every two months from the government's forest ranger programme, which provides aid to those who give up coca production.
"I can't say for sure we will stay out of coca if the money stops," Diaz says. "Without the forest ranger money we wouldn't have any income."
Eighty-year-old Maria del Carmen Flores replaced her 4ha of coca with 10 000 Araza bushes, which produce a tart fruit traditionally used for its juice, but "the fruit is just rotting on the trees because we can't sell it".
Agroamazonia has solved some difficulties by using a Plan Colombia grant to set up a plant to process palm hearts in what was once a coca-growing area outside Puerto Asis.
Wood says, "Alternative development will allow farmers to move into something that over the long term will provide a future for them."
Ten kilometres to the east, Maria Ortensia Benavides isn't so fortunate. She says her cattle and fruit trees don't provide enough income to maintain her family of six and she has no option but to grow coca.
"I have a few cows and I have plantain, but so does every farm for hundreds of kilometres around, so I can't sell it," says Benavides. "Coca sells. I have no alternative."
Farmers like Narvaez have meanwhile found ways to outsmart the eradication campaign. He and his brother, Harvey, plant bushes closer together, hiding them among legal crops. They also use a variety that needs less sun, allowing them to grow in the shade of jungle trees, where they can't be spotted by US satellites.
"Every smart criminal adapts to the situation," says the UN's Calvani.
Harvey Narvaez is, however, preparing to quit the trade for cattle farming. "Coca has become too risky," he says , "but most people don't see a way out of this." - Bloomberg