The fields of Balkh province in northern Afghanistan were completely free of opium poppies this year, a success touted often by Afghan and international officials. But one look at Mohammad Alam's fields tell the story of another emerging drug problem.

Towering, 3-m cannabis plants flourish in Alam's field, part of a wave of farmers turning to marijuana. The crop can be just as profitable as opium but draws none of the scrutiny from Afghan officials bent on eradicating poppies.

Cannabis cultivation rose 40 percent in Afghanistan this year, to 70,000 hectares from 50,000 hectares grown in 2006, the UN Office on Drugs and Crime estimated in its 2007 opium survey.