Regardless of what’s happening in the U.S., it’s not legal in Canada.

A valuable lesson to remember in the world of agriculture: just because something’s happening in the county, province or state next door doesn’t mean it’s okay here.

That’s the case with the use of drones or unmanned aerial vehicles (UAVs) for pesticide applications. The use of drones for chemical applications to manage weeds and diseases is well documented in the U.S., although growers in Western Canada are risking fines of up to $10,000 for drone-applied herbicides and fungicides. They’re still illegal for such practices and Dr. Jason Deveau of the Ontario Ministry of Agriculture, Food and Agribusiness (formerly OMAFRA) believes there are very good reasons for such restrictions.

Size matters
Contrary to their appearance, drones are not miniature helicopters; their flight dynamics -the number of rotors and the airflow they create under the craft -are vastly different compared to a plane or helicopter. With those vehicles, the spray “lays-out” in a level or horizontal flow. Drones constantly force air downward but in a very inconsistent pattern, making deposition into the canopy haphazard.

“The only things that affect spray deposition behind a plane or helicopter are gravity, the wind that blows it around and any forward momentum from the vehicle itself,” explains Deveau, the ministry’s application technology specialist. “Drones always have a downward component, no matter how fast they fly. They’re always in hover or transitional flight, which means they’re always blowing down.”

The number of rotors, droplet size and distribution, and where the droplet’s released relative to the rotor can act together to complicate applications. Fine droplets are susceptible to the wind effects of a rotor: droplets released close to the centre of a drone will have a spinning, tornadic effect. If released near the wing tip, their distribution pattern will be more erratic. Part of that dynamic comes from the number of rotors spinning at variable rates, instead of fixed rates.

“The reason a drone can stay so still is because all the rotors spin at different speeds depending on what the wind is doing,” says Deveau. “The effect of that wind and the down-wash on a droplet changes from moment to moment and it’s not just one of them -it can be four or two or eight rotors.”

Another concern for Deveau is the tank size which is insufficient for higher water volumes, which leads to smaller droplet size and a higher risk of off-target movement. That also changes how the product dissolves and how that droplet reacts when it strikes a plant’s surface. Higher concentrations with lower volumes could work, but other times, the impacts are uncertain -and could be catastrophic.

Further complicating matters is the drone’s weight; empty or full, it affects the pattern of the spray distribution.

What’s next?
More long-term research is needed before producers can be allowed to use drone technology for herbicides and fungicides, and it all comes down to minimizing risk. Many of the efficiencies and nuances of drone technology are unknown, regardless of what sellers of the systems say about careful applications. Thus far research has determined that spray coverage with drones is about five per cent versus conventional systems that are up to 10 per cent.

He adds there are also concerns about operator exposure, drift potential and what happens to the 10 per cent of product that remains in the air. And it’s not just one agency that drones must pass muster -it’s three: Agriculture and Agri-Food Canada (AAFC), Transport Canada and the Pest Management Regulatory Agency (PMRA).

“Many operators want to fly and they want to fly in populated places using heavy drones, which means they have to have their advanced pilot’s license,” says Deveau. “If you’re talking about spreading fertilizer or cover crops, drones are fantastic. If you’re spraying pesticide -and people are doing it -don’t. It’s illegal and it’s not going to work for you -at least not consistently, and when goes wrong, it goes wrong.”