The areas the Funnells have worked in range from Wellington to Lake Tutira in Hawke's Bay across to Waiouru and Stratford.
"The concept of a UAV [unmanned aerial vehicle] in agriculture is a pioneering thing. There's no written training syllabus for people like us. There is very little present-day New Zealand agricultural drone spraying experience to call on," Funnell said.
"As far as I can tell there is only about eight registered for agricultural spraying in the country and trying to get information from them is difficult. Businesses using drones is like a secret squirrel society – we are a new breed.
"At the start we didn't even know what our costs would be, so it was difficult to quote jobs. We decided to charge by the hour and we still only charge for hours flown and not for the total time our crew has been on-site. We could be on-site for say seven hours, but only fly four hours, so that's what is charged."
The Whanganui couple set up Agdrone, seeing an opportunity to provide agricultural spraying services in areas where helicopters cannot fly and ground crew find difficult to access or take twice the time a drone takes to complete a job.
Drone spraying is pinpoint accurate and can hone in on individual weeds that are often scattered around paddocks rather than growing in large bush-like clumps.
"We can spray individual plants and leave the pasture in between spray-free and unaffected. It also uses less chemicals. We can get stuff clinging to cliff faces that even abseilers struggle to access," Funnell said.
"Of course, if there was say 20 acres [8ha] of solid gorse you would get a helicopter in. But if there are blocks of weeds that have native trees scattered throughout, we can isolate them and spray around them.
"Our normal spray height is between 2.5 and 3 metres above the plant. The down wash from the rotors is significant and assists to get an even chemical distribution through the plant.
"Also our spraying speed, depending on what drone we use, is between 3.2km/h and 6.4km/h for woody weeds or 6.4km/h and 13km/h for pasture weeds.
"The big drone in solid gorse can cover up to 1.5 hectares an hour. The small drone [covers] about 0.6ha and around about double that on thistles.
"Each drone has a camera, not to take photographs but to show the pilot exactly when the drone is over a target plant and that's very important when spraying scattered plants at a longer range," Funnell said.
"Our drones are subject to a strict maintenance regime. We complete [checks] daily and do more comprehensive checks every 20 hours. Every 100 hours the craft has to be checked and signed off by a CAA [Civil Aviation Authority] approved technician."
The Funnells are pioneering an efficient and cost-effective system to spray roofs for lichen and moss.
"We have completed the drawing-board stage and hope to begin field trials in about a month's time," he said.
Spraying can only be done in line of sight and pilots have to have an observer with them on jobs.
"We often get people inquiring how to go about operating a drone, but it's not easy, you need to be licensed. I had to go to pilot school, then to chemical school to learn the same stuff a helicopter or fixed wing ag pilot needs to. Then you have to send in an exposition (standard operating procedure) to the Civil Aviation Authority for approval. The increasing number of applications has slowed the process down.
"I'd say it would be the best part of eight or nine months before you would get to spray any chemicals on the ground by the time you qualify."
A visit to one his suppliers on day one of Covid-19 alert level 3 reminded Funnell just how supportive the commercial and farming community have been to him and his wife in the past 15 months.
"Most our new work comes from word of mouth and we are very grateful to live in a region that is so supportive of new ideas and methods."
