The incident on Feb. 3 has left the herders of sheep and goats in this remote mountain area in Helmand Province deeply angered and suspicious. They are convinced that someone is surreptitiously spraying their lands or dusting them with chemicals, presumably in a clandestine effort to eradicate Afghanistan's bumper poppy crop, the world's leading source of opium.

The incident in Kanai was not the first time that Afghan villagers - or Afghan government officials - had complained of what they suspected was nighttime spraying. In November, villagers in Nimla, in Nangarhar Province, said their fields, too, had been laced with chemicals when a plane passed overhead several times during the night.

Afterward, Afghan and foreign officials who investigated returned with samples of tiny gray granules that they said provided evidence that spraying had occurred. Two Western embassies sent samples abroad for analysis but have not yet received the results.

At that time, President Hamid Karzai publicly condemned the spraying. Though it was never clear who was responsible, members of his staff said they suspected the United States or Britain, which together have been leading the struggle to rein in Afghan poppy cultivation, which has reached record levels. Both countries finance outside security firms to train Afghan counternarcotics forces.

President Karzai said his government was not spraying fields and had no knowledge of such activity, and he called in the American and British ambassadors for an explanation. Then, as now, the American and British Embassies denied any involvement.

"There is no credible evidence that aerial spraying has taken place in Helmand," the American Embassy said in a statement this time. "No agency, personnel or contractors associated with the United States government have conducted or been involved in any such activity in Helmand or any other province of Afghanistan."

An Afghan government delegation sent to investigate the latest incident said it found no evidence of aerial spraying. Rather, "a naturally occurring disease" had killed the crops and animals, Lt. Gen. Muhammad Daoud, deputy interior minister for counternarcotics, said in a statement.

Agriculture Ministry officials said the extremely cold weather could have affected the crops. They added, however, that the ministry lacked the technical capacity to analyze samples for chemicals.

But the people in Kanai, neighboring Tanai and at least two other villages are incredulous. For them, there is no doubt that someone sprayed their lands and, despite official denials, they blame the United States, which still controls the skies in Afghanistan.

"They are the ones with the planes," said Abdul Ahmad, brother of the shepherd, Abdullah. Between them, the brothers had lost 200 animals from symptoms that suggested poisoning, he said.

"They went mad, their eyes went blue and they could not eat," he said of their sheep and goats. "Water was coming from their mouths, they were trying to eat their droppings and they were shivering," he said. The animals appeared completely healthy the day before, he said.

"We gave our vote to Karzai so he would bring us help and now he is killing our animals," he said angrily.

While the mystery lingers around who may be responsible for a secret aerial eradication campaign here - or even whether one is actually being carried out - there is no doubt that Afghanistan's booming poppy crop has been an intensifying concern to United States, British and other international officials.

In November, a United Nations report found that more than 300,000 acres in Afghanistan had been planted with poppies and expressed concern that the country was degenerating into a narcostate. American and other officials said they feared the drug trade had insinuated itself into virtually every corner of the Afghan economy and was financing rebels.

Some American officials, particularly those in international narcotics and law enforcement, have for months advocated aerial spraying to gain control of the problem.

Diplomats and other foreign officials involved in agriculture programs and counternarcotics efforts here said there was a discussion in 2004 between American officials and other donors over whether to use aerial eradication to stem poppy cultivation, which expanded 64 percent last year.

In December, the Bush administration presented to Congress a budget request for $152 million for aerial spraying as part of a $776 million aid package for counternarcotics operations in Afghanistan for 2005. In January, it dropped the budget line for aerial spraying because of President Karzai's clear opposition, an American official in Kabul said.

Word of the budget request prompted 31 nonprofit groups, led by CARE International, to sign an open letter to Secretary of State Condoleezza Rice on Jan. 31 expressing concern over what they considered the excessive emphasis on eradication in the United States administration's counternarcotics strategy in Afghanistan.

"Widespread eradication in 2005 could undermine the economy and devastate already poor families without giving rural development projects sufficient time to provide alternative sources of income," the agencies warned. They called for concentration on interdiction of traffickers and support for farmers instead.

Yet American officials have not ruled out the possible need for aerial eradication and financing, which was included in a supplemental request in February for $82 billion by the Bush administration for Iraq and Afghanistan, an American counternarcotics official in Kabul said.

One option considered by American officials last year was to rent civilian planes and spray the general weed killer Roundup over the provinces of Helmand and Badakhshan, two of the largest producers of poppies in the country, according to one official familiar with the plan.

American military officials in Afghanistan and those with the United States Agency for International Development are also against aerial spraying, foreign officials in Kabul say. Development officials argue that spraying will affect all agriculture and especially the poorest farmers; instead, they advocate alternative livelihood programs for farmers to dissuade them from growing poppies.

The military fears that spraying will turn the population against the government and the American presence in Afghanistan and increase support for insurgents, who remain active in southern Afghanistan.

In fact, the belief that they have been sprayed has angered villagers all the more because the local police came here only 40 days before and destroyed their poppy fields on government orders, a fact that the district police chief, Abdul Hakim Karezwal, confirmed.

The farmers said they had instead planted wheat, which was now yellow and rotting along with the clover, spinach and greens they had also planted. Some farmers kept growing small patches of poppies inside high garden walls, but most of the fields in the village showed shoots of young wheat.

"Karzai lied to us," one farmer, Ahmadullah, said. "He said, 'We will give you assistance,' and he didn't. So we grew poppy to be able to feed our families. Then the president ordered it destroyed and so we destroyed it. And now he is destroying our wheat. What will be left of our lives? They destroyed everything. We will have to abandon the village."