Hubert Allen Jr., 72, wounded two other former Pritchett Trucking Company co-workers before killing himself, the Union County Sheriff's Office said in a statement.
Allen shot company owner Marvin Pritchett, 80, and co-worker Rolando Gonzalez-Delgado, 28, at Pritchett's property around 9 a.m. EDT, CBS News reported.
Police said Allen then shot and wounded Lewis Mabrey Jr., 66, after the two "exchanged words" as Mabrey drove a farm tractor on a public road, the report said.
Allen then went to the trucking company where he formerly worked in Lake Butler, Fla., and shot David Griffis, 44, in the stomach.
Police said Allen went to his home in Lake Butler, where he shot and killed himself.
Griffis underwent surgery and was listed in critical condition. Mabrey, who was shot in the arm, was reported in stable and good condition and was to undergo surgery.