Colorado’s plans for a comprehensive system to track recreational marijuana from seed until sale won’t be quite so comprehensive.

Officials from the state Department of Revenue said Thursday the system won’t be able to start tracking marijuana weights until after the buds are harvested off the plant. The revelation came during a meeting of a stakeholder working group going over proposed rules for the forthcoming recreational marijuana industry. And it raised the concern of Ann Marie Jensen, a lobbyist for the Colorado Association of Chiefs of Police who is a member of the group.

Jensen asked how, without keeping track of plants before harvest, the state could be sure that marijuana growers weren’t under-reporting harvest amounts and diverting pot illegally into the black market. Maintaining such control over the recreational marijuana industry is seen as crucial in preventing federal raids against the businesses.

Lewis Koski, the head of investigations for the Colorado Marijuana Enforcement Division, said he understood the concern but that it wasn’t possible to keep precise track of something as variable as plant growth. He said the state would also use other tools — like surveillance systems — to make sure stores are playing by the rules.

“I don’t know that you can suggest that there is a system anywhere that can track 100 percent of the inventory by itself,” Koski said. “It’s part of a much bigger regulatory atmosphere.”

Attempting to allay concerns, medical-marijuana dispensary owner Matt Huron, another working group member, said his business keeps measurements of plants before harvest, then rigorously tracks the weights of finished product and waste materials as a best practice.

“We do not weigh plants but we do record them going from one cycle to another,” Huron said.

Ron Kammerzell, the Revenue Department’s head of enforcement, said Colorado has “reactivated” a $1.4 million contract with a company called Franwell to build a computer system for tracking marijuana batches by radio-frequency tag. The state had previously hired Franwell in 2011 to build such a system for the medical-marijuana industry, but money troubles caused the state to deactivate the contract.

“We think it’s going to play a really important role in helping us accurately tax and assess taxes on the product,” Kammerzell said.

John Ingold: 303-954-1068, jingold@denverpost.com or twitter.com/john_ingold