Drones disperse ladybirds, wasps to control pests on Cape vineyards

The target on Vergelegen wine estate is the mealybug, which spreads the leaf roll virus that damages the vines and reduces the quality of wine

A Somerset West wine estate is testing novel technology to control nasty agricultural pests in its vineyards — drones that deliver beneficial insects. 

The goal of the 324-year-old Vergelegen wine estate, which has clinched several accolades for its environmental initiatives, is less vine disease and higher quality grapes. 

It is working with a local venture, SkyBugs, which is a partnership between FieldBUGS — the supplier of the predatory bugs — and agritech company Aerobotics, which collaborates with a network of drone pilots to disperse the insects accurately.

“It’s always exciting to be part of some groundbreaking work, especially if it means that we can secure food and wine in South Africa,” said Ruan Erasmus, the technical support specialist at FieldBUGS.

The target of the buzzing benefactors are mealybugs, which spread a disease known as leaf roll virus. According to Vergelegen, this disease is much more apparent in red wine cultivars but also affects white wine cultivars. The plan is to target them with predatory wasps and indigenous ladybird beetles.

Leaf roll virus diminishes the quality and volume of the harvest and eventually the vines are not economical and must be uprooted. Erasmus said the tiny sap-sucking bugs are the biggest problem for the local wine industry, and infestations can lead to the removal of a whole vineyard block and thousands of vines. 

“It’s not just because they affect the quality of the grapes; they also eat on the actual vine and stunt its growth. The roll leaf virus that they carry, if they infect the vine, slowly over a year or so, you’ll basically lose production and … you will actually have to remove that specific vine.” 

Drones vs bugs

In October, the first SkyBugs drone dispersal took place at Vergelegen. A total of five dispersals — depending on test results — should be concluded in the first quarter of this year. About 130 hectares of vineyards will receive beneficial insects.

Erasmus said the first stage of the programme involved scouting and data assessment. The actual method of insect release involves flying a drone 30m above a vineyard block. The drone releases insects using a motor-driven mechanism equipped with a cartridge and a drawn-out plastic film, effectively releasing the insects on the vines. 

Each flight covers up to 20ha, after which the drone is landed, and a new battery and cartridge of insects are inserted. The insects are dispersed while in the pupa life stage — between immature and mature insects — and hatch after several days, depending on the weather.

Vergelegen uses predatory wasps (Anagyrus Vladimiri and Coccidoxenoides perminutus) and indigenous ladybirds (Cryptolaemus montrouzieri). The first stage is distributing predatory wasps, which are attracted by a pheromone released by female mealybugs. 

This proactive measure is supplemented with the selective distribution of ladybirds, which can eat 100 to 200 mealybugs daily. FieldBUGS, which has about 15 insect types in its arsenal, sources the predators used at Vergelegen from insectaries in Piketberg and Tzaneen.

Building up populations

“These predatory wasps will actually parasitise a mealybug female,” Erasmus said. “In the insectary, they will basically grow a mealybug that has been stung already so we get that pupa and we release it … a wasp will hatch. All insects are weather dependent so you want to release them when it’s nice and hot and they actually hatch quite soon after release.”

The one wasp would then, by use of a pheromone, find the mealybug female and lay an egg inside it. A new wasp would hatch out of the mealybug. In this way, the mealybug numbers are controlled, Erasmus said.

“The wasps we mainly release via drone and you will only use the [ladybug] beetle if you have big infestations. It’s quite an expensive little beetle, but very effective,” he said. 

“But the wasp you can release proactively before you have the big pressure of mealybugs, just for them to establish as well and build up populations. If they don’t have a host, they can also survive on pollen from flowers in the area.”

The drone flies a zig-zag pattern over the vineyard block, which will slowly and evenly distribute the pupa “and in that way, these wasps don’t have to fly that far to find a host”. 

“So, you give them almost like a head start or an easier kind of distribution to find the mealybug. Also, we’ll load the vines with, let’s say the dosage is 600 [insects] per hectare [and] we’ll put 20% extra just to compensate for if one falls in the road or there are some mortalities.”

Controlling mealybugs in phases

Vergelegen viticulturist Rudolf Kriel said the drone delivery of beneficial insects is the latest phase in a long-term, holistic sustainability programme. Its records show less than 0.05% of leaf roll virus infestation in red varieties, and 0.3% in the white varieties. 

“It is exceptional to have vineyards of this age [20 to 25 years] that are essentially virus-free,” he said, adding that Vergelegen has been the pioneer in many ways for addressing leaf roll in the local wine industry.

The programme to control mealybugs at Vergelegen was implemented in three phases: planting new, intact vineyards; uprooting badly infected red wine cultivar vineyards and replanting them; and testing and treating white wine cultivars that, apart from Chardonnay and Semillon, do not readily show the effects of the virus.

“Vergelegen planned to replace 25ha of citrus with vineyards and, accordingly, in 2002, the first completely ‘clean’ vineyard was planted,” Kriel said. “These vines were regularly tested and any infected vines were removed. The mealybug virus has virtually been eradicated at that first, newly-planted vineyard.”

Growing interest in biological control

Erasmus said there is growing interest in the biological control of pests, especially in the Western Cape where a lot of the fruit is exported. Farmers want to improve their yields, and avoid chemical residue on fruit to meet strict European and Fairtrade environmental standards. 

The bark of vines is coarse. “Mealybug actually live between the cracks and crevasses of vines so it’s very tough to get them with the [chemical] spray so you can miss a lot of insects with chemicals, whereas with these wasps — one is just under a millimetre and one is half a millimetre — you can get underneath the holes and crevasses to find the mealybug and they [the wasps] can lay multiple eggs a day.”

Beneficial insects are traditionally dispersed by buying compostable tubes of insects which are hung in vines. Drone dispersal ensures more effective distribution and coverage, Erasmus said.

Predatory wasps fly no more than 90m daily, so drone dispersal improves the likelihood of the wasps locating mealybugs. Beneficial insects can also be released on high trees near vineyards, where mealybugs normally escape detection. The use of insect pupa on plastic film saves the cost of tube packaging, and offers better value for money.

“One can never completely eradicate mealybugs, but it is possible to control them,” Erasmus added.