Wind speed, wind direction, and field boundary information are detected and used to identify a monitor area indicative of a likely overspray condition. Control signals are generated to deploy an unmanned aerial vehicle (UAV), with a sprayed substance sensor, to the monitor area. The UAV is controlled to reposition it, as a spraying machine moves through the field being sprayed. When an overspray condition is detected, an overspraying signal from the UAV indicating the detected overspray condition is received and overspray processing is performed, based upon the received overspray signal.