Just before 5 p.m., the police received a call that someone was sprinkling powder on the ground. The store was evacuated and remained closed the rest of the day.

The incident prompted a massive response from the New Haven police and authorities from surrounding towns.

Dr. Salchow was at home waiting for the others who took part in the four-mile run to arrive for an after-party when his wife called to say there was a problem. He biked to Ikea and tried to explain to the police that the powder was just flour.

The club’s tactics have caused problems elsewhere.

In 2002, a trail of flour caused a mall in Fayetteville, N.C., to be evacuated for two hours. A few months earlier, two runners in Oxford, Miss., were arrested after using piles of white powder to mark a route through a downtown square.

Dr. Salchow said that after the 9/11 attacks, club members started using chalk to mark courses. But as fears eased, they went back to flour because it is biodegradable. He said they would start using chalk again or find somewhere else to run.

Jessica Mayorga, a spokeswoman for Mayor John DeStefano Jr., said the city planned to seek restitution from the Salchows, and will meet Monday to decide how much.

Ms. Mayorga said they should not have used the flour if they knew it had caused scares in the past.

“You see powder connected by arrows and chalk, you never know,” she said.