Pioneering aerial drone spraying in forestry

January 21, 2021

The Thuthuka Forestry drone spray operation team ready to go (left to right) Innocent Dube (field assistant), Jan-Hendrik Viljoen (mechanisation forester) and drone pilots Wade Harrison and Tiaan Botha. The drones in the foreground, and the support trailer behind.

An innovative silviculture contractor in Mpumalanga, South Africa is pushing the technology envelope, utilising drones to do pre-planting sprays. This is just one of a raft of innovations harnessing the efficiencies of new technology that is rapidly changing the way forestry is practiced in South Africa.

Thuthuka Forestry is one of the leading silviculture contractors in Mpumalanga, with a staff of 340 people.

The company does silviculture, fire prevention and fire fighting work for Mondi, maintaining some 45 000 ha of forestry land around the town of Mkhondo, formerly known as Piet Retief, comprising mainly gum and pine and a little wattle, as well as unplanted areas set aside for conservation.

In the past forestry operations in South Africa, both harvesting and silviculture, have been largely manual or motor-manual. Some 15 years ago Mondi embarked upon a drive to modernise their forestry operations on their South African plantations, working closely with their contractors to develop systems that would improve productivity as well as health and safety.

Thuthuka Forestry has been at the forefront of this modernisation process, introducing various mechanical pitting, planting and spraying machines to good effect over the past few years.

Their latest innovation is the introduction of Remote Piloted Aircraft Systems – or drones - to do pre-planting spraying applications.

“We are always looking at improving production methods and looking for ways to streamline our systems,” commented Thuthuka’s mechanisation forester, Jan-Hendrik Viljoen. “The drones have proved to be highly effective, and have resulted in cost savings and benefits for us and for Mondi. The technology has a lot of potential and could be used for many different applications in forestry. This is just the beginning,” he said.

The drone carries 10 litres of pre-mixed Roundup, and sprays 2 to 2.5 ha per hour from an elevation of around two to three metres above the ground.

Thuthuka currently has two purpose-built aerial spraying drones doing pre-plant sprays in Mondi’s plantations around Mkhondo. They are DJI Agras MG-IPs, equipped with 10 litre tanks and four spray nozzles. Take-off weight with chemical mix on board is 24 kgs. Flight time with fresh battery and full tank of chemicals is 6-8 minutes.

The aerial spraying operation is performed by a team of three - two drone operators/pilots and an assistant. The team operates from a 4x4 bakkie with a specially designed trailer that houses two generators to charge the drone batteries, plus a tank for the chemical mixture, a water tank and safety equipment.

The pilots fly the drones from a platform mounted on top of the support bakkie, which gives them a good view of the drone and the whole compartment to be sprayed.

The operation starts with the mapping of the compartment. This is simply done by taking GPS readings around the perimeter (on foot or from a bakkie) and the control software works out the most efficient flight path for the drone.

Wade Harrison flies the drone from a platform on top of the bakkie, which provides good visibility.

Once the flight path has been mapped and the drone prepped with a charged battery and full tank of chemical mix, it’s lift-off. The two drones are operated together, with one getting a fresh battery and chemical mix refill while the other is in flight. The assistant takes care of re-charging the drone batteries and refilling the chemical tanks while the pilots are busy flying. The pilots clean and maintain the drones regularly.

The team is spraying from an elevation of two to three metres, and are experimenting with different nozzles to improve spray coverage and accuracy. Each drone sprays between 2 to 2.5 hectares per hour. The two drones with a three-person team can spray about 30 ha per day, depending on weather and terrain. In 2019 the team sprayed a total of 1 200 ha, and will do more this season.

Weather conditions are a key factor in efficient aerial spraying operations. Wind needs to be below 7 metres/second and ideally no more than 4 metres/second, and rain is a no-no as it washes away the chemical before it can do its work on the weeds. So they tend to spray early mornings and late afternoons when the wind dies off.

The pump that moves the chemical mix from the tank to the spray nozzles at pressure is programmed to adjust relative to the drone speed to maintain a constant flow. The drone is equipped with radar to maintain the correct elevation above the ground, and pretty much flies itself once it has locked into the pre-planned flight path, although the pilot can interrupt the flight at any point.

Field assistant Innocent Dube refills the drone from a tank housed on the support trailer.

Jan says there are numerous benefits of aerial spraying with drones vs ground-based spraying:-

• The soil in the compartment does not get compacted by vehicles and equipment moving around.
• The aerial spraying application can be done in wet areas, or areas with dense vegetation where ground-based vehicles and equipment can’t access.
• Aerial spraying uses less water than surface application.
• There is minimal wastage of chemical mix and increasing accuracy of application.
• The application can be done ‘just in time’ when timing is critical.

On the negative side, the location of trees, power lines, fences and the contours of the terrain may impact on the efficiency and accuracy of aerial spraying.

This is the second season that the Thuthuka team has been using the drone for pre-plant spraying. Jan says that the results have been excellent, though they are still on a continuous learning curve.

Jan said the drones have the potential to be used for other spraying applications, but Roundup is currently the only chemical registered for aerial application. Drone technology is developing fast, and drones with double the lifting capacity of the model being utilised by Thuthuka are already available on the market.

After the compartment has been clear-felled and the slash removed, the old stumps are clipped off at ground level with a stump clipper and the compartment is ripped with this tractor-drawn ripper. The tyres are dragged behind the ripper to close the rip line. Then the drone does a pre-plant spray, and the seedlings are planted in the rip lines.

The Thuthuka team is exploring the possibility of using the technology for other applications, for example monitoring and measuring tree survival and growth, monitoring the impact of pests and diseases on tree crops, and to provide an eye in the sky for fire prevention and fire fighting operations.

However complying with the legal and safety requirements of aerial spraying with drones, getting the maintenance and support infrastructure in place, not to mention the operations team and the training, is a long and complex process.

“You can’t simply purchase a drone, take it in-field, fill it up with chemicals and make it fly. There are many factors to be considered, including the legal and safety requirements, getting the right crew and putting the logistics in place,” said Jan.

Thuthuka Forestry
Thuthuka Forestry was established when Reuben Ngwenya and Chantelle Snyman bought out an existing silviculture contracting business in 2008. Mondi’s enterprise development division – Mondi Zimele – played a key role in facilitating the purchase, and provided guidance and mentoring in the first few years of operation.

Thuthuka Forestry owners Chantelle Snyman (left) and Reuben ’Shoes’ Ngwenya.

Both Reuben and Chantelle had years of experience in forestry contracting, working their way up through the ranks, before buying the business. Chantelle started off as a receptionist, moving on to fleet management and health and safety officer. Reuben started out as a driver and later a supervisor of silvics teams. He is the Operations Manager for Thuthuka, and Chantelle fulfils the CEO function.

They both know the Mkhondo area well and have a good understanding of Mondi’s requirements for contractors.

The company has been one of Mondi’s shining lights, and has been their Contractor of the Year for 2012, 2013, 2016, 2019 and 2020, and has an outstanding safety record.

Thuthuka currently does contracting work for Mondi and for Mpact (formerly Mondi Kraft) in Mkhondo area.

With the exciting developments in equipment and technology in the silviculture space, the sky is the limit for Thuthuka.

Another Thuthuka Forestry innovation … specially designed mobile living quarters for field staff required to live on site during 24-hour pitting operations. The mobile quarters sleeps six people and has a fully equipped kitchen and bathroom with hot water. It is solar powered.

Related article: Just throw, wait and grow


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