Sprayer drones for Mondi’s forests

An innovative silviculture contractor in Mpumalanga, South Africa is pushing the frontiers of technology, turning to drones for pre-planting sprays as one of the many ways to modernise forestry in the country.

Owned by Chantelle Snyman and Reuben Ngwenya, Thuthuka Forestry is one of the leading silviculture contractors in Mpumalanga, with a staff of 340 people. The company has been at the forefront of modernising its operations, introducing various mechanical pitting, planting and spraying machines to good effect over the past few years. In addition to silviculture, it also offers fire prevention and fire-fighting services to paper and packaging company Mondi, on their 45,000-hectare spread of gum, pine and wattle trees around the town of Mkhondo in Mpumalanga.

Their latest innovation is the introduction of drones, which they are using for pre-planting spraying missions around the forestry.

What happens in the planting process is, before the seedlings can be put into the fallow ground, that ground has to be prepared first; one of the preparatory phases in weeding out grass and other unwanted vegetation.

That’s where the drones come in.

“The drones have proved to be highly effective, and have resulted in cost savings and benefits for us and for Mondi,” says Thuthuka’s mechanisation forester, Jan-Hendrik Viljoen. “The technology has a lot of potential and could be used for many different applications in forestry. This is just the beginning.”

And we are all here for it. Harvesting and silviculture, have traditionally been costly and time-consuming manual or motor-manual undertakings, but in the past fifteen years, Mondi has embarked on a drive to modernise their forestry operations in South Africa, working closely with technology partners to develop systems that would improve productivity as well as health and safety.

As one of the technology partners, Thuthuka’s answer to modern spraying question was to fly in the drones.

Now in their second year with the technology, the company has two purpose-built aerial spraying drones in its repertoire – DJI Agras MG-1P octocopters, equipped with 10 litre tanks and four spray nozzles – carrying out pre-plant sprays in Mondi’s plantations around Mkhondo. Take-off weight for a drone loaded with chemical spray is 24kilogrammes, while full-load flight time is around eight minutes.

The drones can spray between two and two-and-half hectares per hour – or 30 ha each day – from an elevation of around two to three metres above the ground.

The aerial spraying operation is performed by a team of three – two drone pilots and an assistant. The Thuthuka team operates out of a truck with a specially designed trailer that houses two generators to charge the drone batteries; a tank for the chemical mixture; and 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 their drones and the area to be sprayed.

Ready for action. Picture: SA Forestry Online

The drone pilots are usually provided by Cape Town-based drone training services company, UAV Industries.

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 refilling and exchanging batteries 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.

“Weather conditions are a key factor in efficient aerial spraying operations,” Viljoen explains. “Wind needs to be below seven metres/second and ideally no more than four metres/second. Rainy days are a no-no, as rain washes away the spray before it can work on the weeds. For these reasons, the perfect time for spraying is early in the morning, on a dry day and late in the afternoon, when the wind dies off.”

And when the weather odds are in the team’s favour, Viljoen says the benefits of using drone technology over traditional means are immense, which include critical timing, saving on water and spray; and the effectiveness of aerial drones without disturbing the ground or stepping on important vegetation.

The Thuthuka team is also exploring the possibility of using drones for other applications, like 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.

Navigating the legal minefield to obtain an operating licence has been a thorn in the flesh for Thuthuka, as it has been for almost all companies with commercial drone operations in South Africa. Local regulator, the South African Civil Aviation Authority (SACAA) does not just hand operator’s licences on a whim; the application process can even stretch for years.

“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 Viljoen.

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.

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