ASRS 1669809

Aircraft X had previously conducted parachute jump operations. Aircraft Y was a VFR overflight southbound passing east of the airport. Aircraft Y had been handed off to Approach and a communication change completed. I observed a beacon code east of the airport climbing toward Aircraft Y. I suspected the beacon code was Aircraft X. I quickly confirmed beacon code assignment with the EDST (En route Decision Support Tool). Even though Aircraft X hadn't called on frequency, I issued a traffic alert to Aircraft X to turn left immediately just hoping the aircraft was monitoring my frequency. Aircraft X was on frequency and turned left immediately. I gave additional information on the traffic type and location. Aircraft X saw traffic and barely avoided it. Radar targets nearly merged at the same altitude. Aircraft X then stated that traffic information just appeared on "the box." Normal operations then resumed. [I suggest the jump operator] call via land line 10 minutes prior to initiating jump operations to allow for tactical adjustment of non-participating aircraft. [ATC could] sterilize the airspace in a 10 mile radius around the airport from initial call for jump operations until last jump completed. ATC should conduct quarterly telephone conferences and yearly face-to-face meetings with jump operators to ensure that existing procedures are being adhered to and to make any necessary adjustments.