They're seven figure investments in many cases and feature a mind-boggling array of precision agriculture features, but one visiting spray expert cautions farmers there is still a major flaw in the designs of self-propelled boom sprayers.

Tom Wolf, Agrimetrix Research and Training, Saskatoon, Saskatchewan, Canada, told the crowd at last month's Grains Research and Development Corporation (GRDC) that boom instability was a big problem for spray applicators.

"There have been some alarmingly high coefficients of variation (CVs) in tests done with something like a 36 metre boom sprayer travelling at 25km/h, with figures in excess of 25pc and up to 35pc, well above what we would expect as an acceptable standard at around 15pc."

He said in Canada the transformation to self-propelled units was virtually complete, however, unlike Australia, there has not been as much adaptation of spot sprayers due to the reduced window for using green on brown technology for a knockdown.

"The farmers are very enthusiastic about a lot of aspects of the drones, such as being able to operate remotely and to reduce soil compaction during the wet but there are a lot of things that need to be worked through before they can really take off."

In Australia, the registration to be able to conduct drone spraying is done not via agriculture departments but via the Civil Aviation Safety Authority, which has several clauses, such as one operator per drone, meaning functions such as swarm spraying, where drones were attached for greater efficiency, is not permitted.