A method for controlling unwanted organisms on a field includes providing an electronic map with expected locations of unwanted organisms in the field entered in georeferenced form and a machine with a supply of agent for treating the unwanted organisms and an output device for controllably applying the agent. The method further includes traversing the field with the machine for application of the agent for controlling the unwanted organisms from the output device, detecting organisms in the field by a sensor on the machine during the traversing step, using the map to controllably guide the machine along the field to the location of unwanted organisms, and controlling the output device to disperse the agent on the field when the sensor detects unwanted organisms.