In many parts of the world, crop protection agents will be spread by drones in the future. The new technology places special demands on the spray mixture. Evonik has found a formulation that prevents unwanted drift and distributes the active ingredients as well as possible on leaves
Although thrips are just one millimeter long, farmers fear the tiny creatures because they can cause great damage, especially in subtropical and tropical regions. The insects with the characteristic fringed hairs on the edges of their wings eat the leaves and flowers of many useful plants, such as cotton, tomatoes, and tea. They also transmit viruses that kill many plants. This makes thrips one of the most dangerous plant pests—including in India, where, according to the country’s Tea Research Association, around 150,000 tons of tea are lost every year due to infestation by thrips and their caterpillars. That’s around 15 percent of the entire harvest.
Farmers have been using sprays for decades to keep crop pests at bay. In industrialized nations, these are usually sprayed using tractors, while in developing countries and emerging markets they are often applied by workers who carry the spray mixture in tanks on their backs. However, drones are very likely to be buzzing over Indian fields and farmland more frequently in the future. Flying low, they will spray crop protection agents to combat insect pests and pathogens.
Carrying 100 kilograms across fields
Just a few weeks ago, the Indian Ministry of Agriculture was one of the first in the world to give the green light for the use of drones in agriculture. In a standard operating procedure (SOP), the ministry specifies how the UAVs are to be used. Drones are now also a major agricultural topic in other countries such as China and Brazil. The necessary technology already exists. In recent years, models that can carry weights of 100 kilograms and more have come onto the market, particularly in China, but also in Germany and the USA. According to a recent industry study, the market for agricultural drones could grow to an annual volume of more than nine billion US dollars by 2028—three and a half times as much as in 2022.
The use of drones requires manufacturers of agricultural chemicals to adapt their products to the new technology. If crop protection agents are sprayed in flight, the droplets can be blown further away (drift) by the wind than if they are sprayed by tractors or hand sprayers. To prevent this from happening, the agents need to contain chemical additives. Evonik is at the forefront of the development of these specialty chemicals. “This topic fits very well into our strategic innovation portfolio and is driving the development of our product portfolio in the agricultural sector,” says Dr. Nina Hoppe, who heads the research and development department for the Interface & Performance business line at Evonik in Essen.
In the run-up to the large-scale use of drones in India, the ministry has issued a directive that obliges farmers and drone pilots to prevent crop protection agents from drifting. “In many areas of India, the plots are quite small. Moreover, farmers often grow different crops and fruits on adjacent fields,” says Sachin Vishwakarma, an expert in applied agricultural technology at Evonik, who is based in the western Indian city of Thane.
»The adjuvants will be a blockbuster in India«
Sachin Vishwakarma expert in applied agricultural technology at Evonik
In the run-up to the large-scale use of drones in India, the ministry has issued a directive that obliges farmers and drone pilots to prevent crop protection agents from drifting. “In many areas of India, the plots are quite small. Moreover, farmers often grow different crops and fruits on adjacent fields,” says Sachin Vishwakarma, an expert in applied agricultural technology at Evonik, who is based in the western Indian city of Thane.
Control of insect pests
Vishwakarma is a member of an Evonik team that has been working in recent years to eliminate the drift of crop protection agents. This is accomplished by adding substances to the spray mixture that cause the droplets to fall to the ground or onto the plants before the wind carries them away.
The development of these additives and auxiliaries, which are known as adjuvants, took several years. Last winter, Vishwakarma and his Indian colleagues tested the agents in the field for the first time. His conclusion was: “The results are convincing. We see no discoloration, burns or other damage on crop. On the contrary, it effectively controls insect pests such as thrips.”
From a chemical point of view, the development of adjuvants is a fine art because they have to have very different effects when sprayed. Firstly, the droplets that are released from the spray nozzle should fall quickly to the ground so that the wind doesn’t carry them away. Secondly, they should adhere to leaves and not roll off like rain. Otherwise the protective effect would be lost. Thirdly, the drops should wet the leaves as well as possible so that the active ingredient can penetrate them over a large area. As a result, the spray agent must not remain on a leaf in the form of spherical drops. Rather, the drops should cling to the leaf and spread out on it. In order to fulfill all these functions, several ingredients with precisely coordinated properties have to be combined in an adjuvant.
To accomplish this, the team from Evonik developed the adjuvant BREAK-THRU® MSO MAX 522. Trisiloxanes—compounds of silicon, oxygen, and carbon which Evonik has been producing for many years—are one important ingredient. They are used in many different ways in industry—for example in polyurethane foams or paints and varnishes as well as in many technical applications.
When used in the field, the adjuvant should deliver the spray agent as precisely as possible to the target. “Drifting also occurs when tractors are used,” says Dr. Joachim Venzmer, an expert in interfacial technologies at Evonik in Essen. “But the problem is exacerbated when you use drones.” To reduce this effect, plant-based thickeners can be added to the spray mixture, usually guar gum obtained from the guar bean. This means that only large droplets are produced when spraying, which fall directly to the ground or onto the plants.
The disadvantage is that the thickened liquid can no longer be sprayed well. The spray cone becomes narrower and therefore only wets a narrow strip of field. A guar rubber solution would be completely unsuitable for drone use. The device would have to make very many flights over a field to spray it completely. Venzmer has therefore addressed the drift problem differently, for which he reached deep into his physical bag of tricks.
Understanding water droplets
In the wind tunnel, you can observe how water droplets emerge from a spray nozzle. They first bulge out to form a pocket until they finally rupture and form many small spray droplets. The earlier the pocket ruptures, the larger and heavier the droplets are, and the less widely they spread in the surrounding area.
From pocket to water droplet
“As chemists, we initially didn’t understand the physics of spraying and atomizing at all” he says. He came closer to the solution when a doctoral student at the Technical University of Darmstadt investigated the atomization of jet fuel in a nozzle a few years ago. The researcher wanted to answer the question of how and when a liquid film ruptures and splits into fine droplets. “I stumbled across this doctoral student by chance,” says Venzmer. This [TS1] proved to be a lucky encounter. Joachim Venzmer asked him to use the experimental setup, a small wind tunnel with a high-speed camera, to investigate how a film of water ruptures at a nozzle. A model experiment showed that a droplet in the air stream first bulges out into a pocket before it breaks. If it ruptures early, this is good, because then larger drops are formed. If, on the other hand, the pocket expands greatly before it ruptures, very fine droplets of spray are produced which are easily carried away by the wind.
The goal was thus clear: The aim was to control the rupture of the water film after it emerges from a nozzle in such a way that, firstly, droplet formation is not hindered and, secondly, the resulting droplets aren’t too small.
This meant that the pocket shouldn’t rupture too late. Fortunately, one of the trisiloxanes already performed this task quite well. But it wasn’t yet enough for the drones. The team had to continue working on the right mix of ingredients.
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“This better understanding of the physics of droplet formation has brought us the decisive step forward in the development of the adjuvant,” says Dr. Annika Dietrich, a chemist in Evonik’s Applied Agricultural Technologies unit. The challenge ultimately lies in the fact that a spray agent has to fulfill so many different functions: from droplet formation to spreading on the leaf. “When formulating, we therefore always look for ingredients that ideally fulfill several functions,” says Dietrich. Dietrich and her superior, René Hänsel, have found such a multifunctional substance in the vegetable oil contained in BREAK-THRU® MSO MAX 522: The oil not only causes the spray film to rupture earlier, so that sufficiently large drops are produced, it also ensures that the leaves absorb the active ingredient very well. Another benefit is that the oil forms a particularly water-resistant film once it has dried. This means that the active ingredient adheres firmly to a leaf for many days and is barely washed off by rain.
Is it still drizzling or is it already raining?
In order to optimize this effect, the research teams in Essen and Marl carry out numerous “rain resistance tests”—in simple plastic boxes from the furniture store. For this purpose, the adjuvant is applied to films whose water-repellent properties are similar to those of a leaf surface. To determine how well different adjuvant formulations adhere, they are mixed with a dye that fluoresces under UV light. For the test, the film is sprinkled with water, dried, and then placed under a UV lamp. Depending on how much adjuvant—and therefore also dye—was washed off, the area on which the sample was applied fluoresces more or less strongly,
The team has already developed many variants, reports Nina Hoppe, who coordinates and manages the project: “For example, we are seeing increasing interest from our customers in biodegradable adjuvants made from renewable raw materials. We have therefore developed a formulation that does not require trisiloxane.”
Instead, a polyglycerol ester is used, a substance made from plant-based raw materials, which is also an important component of cosmetics. It has good anti-drift properties, spreads very well on the leaf, and is also rainproof. The adjuvant has now been launched on the market under the name BREAK-THRU® SP133. “For our customers, we keep an eye on the regulations in the various agricultural markets worldwide to ensure that the product meets all requirements,” says Hoppe. To prevent the spray agent from drifting, for example, many countries stipulate that droplets must have a diameter of at least 135 micrometers. The new adjuvants easily achieve this value.
Used from China to Brazil
The market could develop rapidly in the coming years. “We are currently seeing strong interest in drones, especially in India, China, and other Southeast Asian countries,” says Diego Abreu, Head of Marketing at the Interfaces and Performance unit in Evonik’s Agriculture segment. Drones that hit their targets with pinpoint accuracy with the help of the new adjuvants will be a key element of precision farming in the future.
“The business models for which the drones are used can vary widely,” says Abreu. In less developed countries in particular, few farmers can afford an aircraft, which can easily cost several tens of thousands of euros. “In China, for example, drone spraying are being mostly offered by the agricultural retailers that also sell the crop protection agents,” he adds.
Abreu expects that Brazil and other Latin American countries will also have significant drone markets soon. In Europe, on the other hand, tractors will probably continue to be used in the coming years because the authorities are rather hesitant when it comes to approving aerial application technologies for pesticides.
One of the advantages of UAVs is that they significantly reduce water consumption. This is a great advantage, especially in dry regions.
Drones can’t carry as much water as a tractor. Therefore, special formulations must be used in drones, where 10 to 40 liters of water are already sufficient to apply the same amount of pesticide per hectare as 200 to 1,000 liters of water for conventional sprays. In addition to new formulation technologies, this approach mainly requires the new adjuvants. Among other things, these adjuvants ensure excellent wetting of the leaves and spreading.
As the first field test in India has shown, plants can cope very well with the high concentration of active ingredients and the added adjuvants. Further trials are planned for the coming months. Sachin Vishwakarma and his team will test the drone on other crops in order to perfectly adjust the mixture of spray liquid, adjuvants, and active ingredients. The official market launch for drone use is planned for 2025. In view of the advantages that the technology offers, Vishwakarma is already certain that “the adjuvants will be a blockbuster here.”
