Luckily for the students the village school was closed the day that crop-dusters, escorted by combat helicopters, doused the tin-roofed classrooms with herbicides. Their target was the swath of illegal coca plantations on the low hills around the village, but clouds of defoliant engulfed the school, the Roman Catholic church, and the fields of plantain, cassava and maize.
Miriam Rodriguez, a teacher at the school, said: "The effects have been catastrophic. They sprayed the coca, but they also killed all our food crops."
The schoolchildren complained of rashes, headaches and vomiting after the weedkiller fell. Nearby are half-dead fruit trees, withered maize plants and row upon row of skeletal coca plants.
George Bush will meet the Colombian president, Andres Pastrana, in Washington today as the biggest offensive against drugs ever released on Colombia rolls across the southern jungles and farmland.
The blitz on the coca fields is at the heart of Plan Colombia, a $1.3bn (£900m) strategy to cut drug production by 50% and weaken the leftwing guerrillas and rightwing paramilitaries who finance their operations with its profits. Official US figures put Colombian cocaine production at 520 tonnes a year, but analysts say the figure is likely to be much higher.
Guided by spy planes and US satellites, crop-dusters criss-crossed the skies of Caqueta state in the south and the Middle Magdalena region in the north last week. Flying as low as 15 metres (50ft) they were protected by helicopter gunships. Guerrillas of the Revolutionary Armed Forces of Colombia (Farc) often shoot at the slow-moving crop-dusters.
The pilots, some of them US contract workers, fly up to five missions a day, spraying on average 3.8 litres of glyphosate herbicide on every hectare.
Senior Colombian officials say the operation is a resounding success: in the first phase, 29,000 hectares of coca were destroyed in the Guamuez valley in Putumayo state, a lawless region on the Ecuadorian border where nearly half of Colombia's cocaine is produced.
But local farmers and officials say crop-dusting has destroyed thousands of hectares of food crops and pasture, devastated the local economy, and sown deep resentment among the rural poor.
"Why should I lie? I had coca. But they've left me with nothing - no work, and no food," said Otoniel Urrea, staring down at his devastated smallholding in a barren gully stripped of vegetation.
Officials say crops are only sprayed after they have been identified as illegal drug plantations, but in high winds the herbicide can drift off target. Farmers often intersperse coca and opium poppies with food crops, making mistakes even harder to avoid. The effects of spraying are not seen straight away, but several days after fumigation, every plant in the affected zone starts to wither and die.
Farmers say that poisoned ground can take months to recover. Mr Urrea says coca was his only source of cash. The nearest city is Mocoa, 12 hours away down a rutted singe-lane road, and transport costs make most legal crops unprofitable to grow.
In some regions, the government has signed pacts promising emergency food aid and long-term development assistance for farmers who tear up their own crops.
Officials describe the Guamuez valley as a vast network of industrial coca plantations financed and managed by drug dealers. Locals disagree.
"It's not one person with a huge plantation, it's a chain of little crops," said Alfonso Martinez, a former mayor in the town of La Hormiga.
"The government has never had a serious social policy in the Putumayo - and they still don't. Two months after they fumigated we still haven't seen any aid," he said, warning that some peasants, despairing of government aid, were already replanting their illegal crops with a new strain of high-yield Peruvian coca.
"There has been a delay, but that's because we're setting up a social programme which is unprecedented in Colombia. We really believe we can solve Putumayo's problems," said Gonzalo de Francisco, who is in charge of Plan Colombia's social development programmes.
At today's meeting in Washington, Mr Pastrana is expected to ask the US for up to $500m a year in extra financial assistance, and trade preferences to help bail out the struggling Colombian economy.
With unemployment nudging 20%, he believes that the anti-narcotics campaign and peace talks with Farc both depend on social investment. He has warned that without greater investment in drug-producing regions, poor Colombians will continue to work in the drugs trade or sign up with the armed factions which have perpetuated Colombia's 37-year civil war.
Most of the first tranche of US aid went towards helicopters, equipment and training for the elite anti-narcotics army battalions leading the fumigation drive.
Troops from the new battalions patrol the roads leading into the Guamuez valley, but towns in the region are dominated by paramilitary groups. In La Hormiga, militiamen with hand-guns in their waistbands keep watch in the town square.
Late last year the paramilitaries launched a campaign of massacres and assassinations to drive out the Farc guerrillas, who had dominated the region for decades. Their success helps explain the lack of guerrilla resistance to the fumigation campaign in Putumayo.
In rebel-dominated Caqueta state, however, fumigation sorties have come under heavy ground fire, and last week an armed rescue unit - including US civilian contract workers - braved guerrilla bullets to save the crew of a downed police helicopter.
But the brunt of the anti-narcotics campaign has been borne by small farmers and Indians, said German Martinez, a local ombudsman in the town of Puerto Asis.
"If this is just about destroying coca crops and burning labs, no matter the price, then it's a victory," he said. "But if you don't tackle the social causes, the peasants will continue growing illegal crops. We shouldn't just be eradicating coca - we should be eradicating poverty."
© Guardian Newspapers Limited 2001