Ghundy Ghar, Afghanistan ? The gunfire and explosions echoing across this Taliban-infested district in southern Afghanistan on Friday signaled the end of the opium poppy harvest as militants again turned their attention from agriculture to attacking NATO and Afghan forces.

U.S. Army soldiers perched on this small hilltop base in Kandahar province’s Zhari district had a ringside seat to the early morning fighting. It snapped a lull in violence that had lasted almost three weeks while the Taliban focused on taxing the poppy crop, one of its main sources of revenue.

Building up resources is especially important for the Taliban this year as NATO is ramping up its latest military operation in Kandahar, the group’s spiritual heartland. Military commanders have characterized the Kandahar mission as the make-or-break battle of the nearly 9-year-old war.

“This is the most gunfire that has happened in weeks,” said Staff Sgt. Aaron Christensen, looking down from Strong Point Ghundy Ghar as helicopter gunships pounded Taliban militants who had attacked a U.S. patrol about 1.5 miles away. “The poppy harvest is definitely over.”

Afghanistan produces the raw opium used to make 90 percent of the world’s heroin, and the Taliban earn about $300 million per year off the trade, according to the United Nations.

Kandahar itself produced about 16 percent of Afghanistan’s opium poppies in 2009, the second-largest amount after neighboring Helmand province. The key districts in Kandahar for poppy are Zhari, Panjwai and Maiwand.

“I really underestimated how much the poppy harvest would impact the Taliban’s operations out here,” said Capt. Ryan Sheeran, the company commander whose First Platoon is currently based at Ghundy Ghar but also operates in Maiwand.