History
Crop dusting became popular early in the 20th century, as it provided an efficient way for a farmer to apply strengthening and protective chemicals to a large number of crops. By the beginning of the 21st century it became viable for smaller farms to utilize a newer, smaller version of the crop duster.
Mini
Miniature crop dusting can be implemented with remote control (RC) aircraft that are much smaller and less expensive to purchase and maintain than normal airplanes.
Viability
While spray systems can be attached to RC aircraft, mini crop dusters have the drawback of not being efficient for large farms due to a vastly decreased payload. Building one requires someone with a bit of technical know-how as mini crop dusting systems are not yet commercially produced as of Jan. 2011, but they can be a fun project.