Lisa Silverman, 49, a drug prevention specialist, told the 22nd District Agricultural Association she saw widespread marijuana use during a concert by the reggae star at the Del Mar Fairgrounds in August, the San Diego Union-Tribune reported Monday.

"There were very few attendees who were not smoking marijuana," Silverman said.

Board members promised to investigate the matter and one official said the body may consider avoiding music groups that tend to attract pot smokers to their concerts.

"The ball is in their court," Tim Fennell, the fairgrounds' general manager, said of concert attendees. "Don't jeopardize the music you like by doing something improper."

Kenny Weissberg, a veteran San Diego concert promoter, said reggae, hip-hop and classic rock groups tend to attract the most marijuana smokers. He said keeping marijuana away from outdoor venues might not be a realistic goal.

"If people want to get high, they will get high no matter what the regulations are," he said.