KABUL – Afghanistan's opium yield is likely to drop as much as 30 percent this year because blight is destroying fields full of poppies in the south — driving up prices amid a countrywide push to grow legal crops, a U.N. official said Thursday.

Higher prices also could mean more money pouring in to the Taliban, which funds much of its insurgency with profits from the drug. Afghanistan supplies 90 percent of the world's opium, the main ingredient in heroin.

The blight, which turns the poppy plants black as they apparently rot from the inside, has hit about half of the poppy crop growing in the northern part of Helmand province — the center of Afghanistan's poppy production, said Jean-Luc Lemahieu, the top official for the United Nations Office on Drugs and Crime in Afghanistan. It is also significantly affecting crops in southern Helmand and in neighboring Kandahar province, he said.

The lower yield on the surface seems to be a boost to reducing opium poppy cultivation, but it is leading to wild price speculation that instead could encourage farmers to plant more poppy next year.

The price of fresh opium has jumped 57 percent from last year to about $85 a kilogram in April, while dry opium prices are up 37 percent, according to U.N. data.

Prices spiked similarly in 2001 to 2003, peaking at just over $300 a kilogram and sparking a surge in opium poppy cultivation over the next few years. That followed the former Taliban regime's virtual eradication of opium growing during its last year in power before it was ousted in 2001.

"We are monitoring those prices with the utmost caution because the last thing we'd like to witness is another gold rush as during 2001-2003," Lemahieu said.

A spokesman for the Afghan Counter Narcotics Ministry said that higher prices mean interdiction efforts will get more difficult.

Zalmai Afzali said a team for the ministry working on poppy eradication was just attacked in eastern Nangarhar province a few weeks ago and more funds for the insurgents will likely mean more attacks.

The Afghan government has made progress in recent years in getting provinces declared "poppy-free" and by offering incentives to switch to legal crops.

However, the poppy crop in Helmand and Kandahar has proved stubbornly resilient despite falling prices and stepped-up interdiction efforts. The U.N. had previously forecast that this year's opium poppy yields would remain in line with last year.

It is still unclear what is causing the blight, including whether it is a disease or a small insect. U.N. workers have collected samples since it started showing up a month ago and sent them to labs in India for analysis.

Though there has been speculation that a poppy-killing blight could have been introduced in secret by NATO forces, Lemahieu said this was unlikely.

"My inclination is that this is natural," Lemahieu said. He noted that a blight that appears to be similar has hit Myanmar and India, and said there are some indications that it is also affecting other crops, including fruit trees like apricot and apple.

A spokesman for NATO and U.S. forces rejected outright the idea of a military plot by NATO's International Security Assistance Force.

"The idea that NATO or ISAF could be responsible is absolutely ludicrous," Col. Wayne Shanks said. "We are not in the eradication business. What we do is take action where we see the nexus between the insurgency and the drug trade." This means going after financing or interdiction of those smuggling the
drugs.

Farmers' crop calculus could go many ways next year — they could decide the higher price is worth the risk of planting an illegal crop, they could feel they have no other option but to plant high-price opium poppies if there other fields have been decimated, or worries about a return of blight could discourage poppy planting.

"The farmer might be scratching his head and saying 'I can earn a fortune but I can also lose it all," Lemahieu said.

The U.N. hopes that widespread efforts to step up interdiction and introduce alternative crops will hold, but the higher price could provide a hard-to-combat incentive.

"This short term gain could turn around with a vengeance if the licit crops are suffering, if the speculation is not tempered," he added.