The advances in agricultural robotics bring autonomous robots to work in farms. Farm Management Information Systems (FMIS) are sophisticated and complex systems to support production management in farms. They need to integrate software for the scheduling of a fleet of such robots. As agricultural systems are by nature subject to unpredictable events, it seems necessary to provide a solution for online scheduling. After the description of the problem, which is to schedule tasks for the robots in order to fulfill demands for agricultural activities, we propose an online approach based on solving a Mixed Integer Linear Programming (MILP) problem at each step, meaning each time the FMIS is requested to adjust or complete the schedule.