Opium production in Afghanistan fell by one-third this year but due more to bad weather than government efforts to curb poppy crops.

The U.N. Afghanistan Opium Survey 2012 said the government destroyed nearly 9,700 hectares of poppy crops this year, up from around 3,800 hectares last year.

But the amount of land dedicated to cultivating opium poppies, from which heroin is made, rose 18 percent to 154,000 hectares, the 28-page report by the U.N. Office on Drugs and Crime said.

The high level of opium prices reported in 2011 was one of the principal factors that led to the increase in opium poppy cultivation this year.

Despite the rise in the number of hectares under cultivation, the report estimated potential opium production was down 36 percent to 3,700 tons this year.

"This was due to a decrease in opium yield caused by a combination of a disease of the opium poppy and adverse weather conditions, particularly in the eastern, western and southern regions of the country," the report said.

Around 95 percent of all cultivation was in nine provinces in Afghanistan's southern and western regions, which include the most insecure provinces in the country.

The number of poppy-free provinces -- those with less than 100 hectares found under cultivation -- remained unchanged at 17.

Around 22 percent of farmers, when asked why they stopped cultivating opium, cited the government ban as the main reason. Religious belief -- opium cultivation being against Islam -- was the second most cited reason by around 16 percent.

Fear of government reprisals, listed by 15 percent of farmers asked, was the third most cited reason.

The withdrawal of Western troops from Afghanistan by 2014 may result in a surge in production of opium poppies, a report by The New York Times said in May.

"Some money is available through the licit economy but less than in the past as Western contracts dry up, and so the importance of the illicit, informal economy will increase," Jean-Luc Lemahieu, director of the U.N. Office on Drugs and Crime in Afghanistan, told the Times. "The prognosis post-2014 is not a positive one."

Some Afghan farmers said they indeed had little choice but to turn to the profitable poppy.

"I don't have any cash now to start another business, and if I grow any other crops, I cannot make a profit," Mohammed Amin, a poppy grower in Oruzgan province, said.

The Times report predicted this year's poppy crop in southern Afghanistan is expected to be lower due to bad weather and blight. But the consequence will likely be that poppies from other parts of the country will fetch a much higher price for the struggling farmers.

The government's best intentions and efforts to eradicate poppy crops often fail because of corruption.

"When we plan an operation, we have to have approval of the local police chief or his deputy or the zone police chief, and if one of those people is corrupt or linked to a big trafficker, it leaks," said the deputy interior minister for counter-narcotics, Lt. Gen. Baaz Mohammed Ahmadi.