LASKAR GAH, Afghanistan (Reuters) - With livelihoods threatened by a mysterious blight on opium crops, many farmers in southern Afghanistan suspect policies of the U.S.-backed government of President Hamid Karzai may be behind the disease.

With anti-U.S. feelings pervading Helmand and Kandahar provinces, some of the worst hit by insurgent violence, the blight that may cut opium output by half has played into deeply-held suspicions of the government and foreign troops.

Few farmers appear to believe nature was the cause. Some farmers blame a new fertilizer they were forced to obtain after the government banned ammonium nitrate, which can also be used by insurgents to make bombs.

“I have had not only my poppy affected, but wheat farms too and I suspect it is due to a type of fertilizer that is imported from Pakistan,” said Janan, a farmer near Helmand’s provincial capital of Lashkar Gah.

“People have had their other type of crops suffer too as a result.”

Afghanistan is the world’s biggest supplier of opium, a thick paste processed to make heroin. About 90 percent of the crop is harvested in southern Helmand province where thousands of U.S. troops are fighting an insurgency partly funded by the trade. While the blight may cut off some sources of funding for the Taliban in their southern stronghold, the disease may only spark more farmer resentment and play into the insurgent’s hands. It could also encourage more crops as the price increases.

“All indications to us ... seem to hint toward a natural plight,” said Jean-Luc Lemahieu, United Nations Office on Drugs and Crime (UNODC) head in Afghanistan, told Reuters in Kabul.

“Any plague, even if there was a plague on the melons, (the farmers) would blame it on the U.S. So this definitely will be the same thing, so there definitely will be a negative impact.”

General Dawud Dawud, deputy minister of interior for drugs eradication, said in some areas it has destroyed 70 percent of the poppy harvest. The disease has so far been reported in Helmand, and neighboring provinces of Kandahar and Uruzgan.

Lemahieu said that in northern Helmand roughly 50 percent of the plants were affected by the disease which turned leaves into clusters of black dots. In southern Helmand 25 to 30 percent.

The international community has spent years trying to reduce dependency on opium for poor farmers who are reluctant to switch to licit crops because they are less profitable.

But rising violence in the region over the last year has hampered these efforts, and the blight may just add to troubles.

A PYRRHIC VICTORY?

“Are we unhappy with this blight? Well the first reaction is one of “hooray,”” said Lemahieu. “But this might be proven to be a Pyrrhic victory. Because at the end of the day if the price sky-rockets we might have far more opium next year.”

Past Afghan government efforts to eradicate poppy have turned communities against the government and foreign troops. Wary of this, U.S. Marines in the Helmand town of Marjah have employed a strategy of paying farmers to burn their own crops.

Villagers who rely on opium poppy cultivation have accused Western forces of deliberately planting diseases to wipe-out the plant. NATO-led forces in Afghanistan deny any involvement by the alliance in the current blight.

Noor Mohammad, a farmer in Khakriz village near Lashkar Gah, also blamed the fertilizer.

“We haven’t had these disease problems in many years but since we use a new fertilizer, provided by the government, that could have affected my crop.” Mohammad said. “It could be the government trying to destroy the poppy.”

Whatever the accusations, authorities may need to reach out quickly to farmers or face a backlash.

“The disease will not only destroy the poppy this year but the whole crop including wheat and fruit,” said Khan Mohammad, an Agriculture official in the Helmand.

“The government must help the farmers ... otherwise this catastrophe will badly affect the lives of millions.