By Mark Price From The Charlotte Observer CHARLOTTE, N.C.—The city of Winston-Salem is working to evacuate 6,500 people as fears grow a smoldering fertilizer plant might explode near thousands of homes. Fire trucks patrolled the mandatory evacuation area early Tuesday, blowing their horns and loudspeakers blasting a warning for people to evacuate as quickly as possible. The mass exodus is due to a potentially explosive fire at the Weaver Fertilizer Co. in north Winston-Salem. Just under 2,500 homes are within a mile of the plant, which stores tons of explosive materials as part of its products, the city said in a tweet. Residents being are told to plan on being out of their homes for at least 48 hours, and roadblocks have been established around the area. A “reverse 911 call” went out at 6 a.m. Tuesday, to reach those who hadn’t yet left their homes. The Education Building at …