AgriDrones: pros and cons of using UAVs for plant protection in agriculture

Recently, the use of agricultural drones has been rapidly increasing all over the world. No wonder – they allow you to map fields quickly and accurately; assess the condition of crops; notice problem areas that require the attention of an agronomist in time; and evaluate the effectiveness of certain agricultural practices. In many countries, they are increasingly used for plant protection.

What are the advantages of AgriDrones?

- Agricultural drones have high productivity, allow to protect a large area in a short time.

- Agridrones fly on a predetermined route, which prevents the overlap of the spraying lanes and does not leave unsprayed areas, as happens with tractor-propelled sprayers if they are not equipped with GPS.

- Agricultural drones can carry out spraying in conditions when tractor is simply not able to go into the field after rains.

- During periods of high rainfall when fungicide applications are needed but the weather and soil conditions do not allow spraying, the agridrone can quickly do this in the short ″windows″ between rains.

- In fields with irregular topography, which is typical for many countries, it is not uncommon for rainfall to wash soil from high ground into lower areas of the field and they remain damp for a long time. Tractor sprayers get stuck in such places along the axis, which spoils the soil structure and often makes the much-needed cultivation simply impossible. There are situations when in some places of such fields the plants have already sprouted and urgent treatment is required, while in other places it is too early to carry out. It is possible to quickly spay individual sections of the field only with an agro-drone.

Personnel issue – who will be responsible for the use of agricultural drones on the farm?

Agricultural drones are not suitable for the application of plant protection products in all cases, and agronomists must make a responsible decision about their use on case per case basis.

If a large farm can afford to purchase an agridrone and train a pilot, then in many smaller farms it is more economical to resort to service companies, as is done, for example, in Ukraine and Georgia.

It is important for the user – agronomist, or farm owner – to understand the division of responsibility. The pilot is only responsible for the technical condition of the agridrone and the quality of the work. He is not responsible for the effectiveness of the spraying. The choice of terms and weather conditions for spraying, the type of plant protection products or mixes, the concentration of the working solution should be the responsibility of the agronomist. On a small farm where there is no agronomist, its owner who’s responsible. This is an important point that is often underestimated.

″Air pockets″ of plant protection with AgroDrones

Spraying fields and gardens is not a ritual, but an important element in the systematic approach to the plant protection. Spraying efficiency depends on a number of factors and often on their combination. For each cultivated plant, the phases are known when it is more or less susceptible to certain infections or damage by pests, as well as the conditions under which the plant can be more or less affected by the action of pesticides. For example, the thickness of the wax coating on the leaves could impact it. For each harmful organism, the phases of development are known in which it is most vulnerable to the action of a particular chemical.

For each chemical plant protection product (PPP), the conditions for its most effective use are known at least to the representatives of the manufacturer: dosage per hectare, concentration of the working solution (often expressed as the recommended amount of water for spraying per hectare), weather conditions for efficient use (usually the air temperature and the length of time after which the agent is not washed away by rain). For some products, the size of the droplets of the working solution is important, and for microbiological agents, the intensity of solar radiation is also very important.

It is precisely these factors that are the ″air pockets″ of the use of agridrones in crop protection.

Under normal conditions, the amount of working solution depends on the crop or weed species (leaf surface area) and ranges from 150-400 l/ha for field crops and vegetables and up to 1,000-2,000 l/ha for orchards. The size of the agridrone tank is 16-40 liters, that is, the concentration of the working solution increases by 10 or more times. This is fraught with burns of cultivated plants.

Often it seems that it is possible to reduce the consumption of the chemical using a higher concentration of it, but this is not always the case.

For microbiological preparations, an increase in the concentration of the working solution is not dangerous, and can even increase the efficiency of their use. Under normal conditions, it takes some time until a population of microorganisms diluted 100 or even 1000 times reaches an effective size. The lower the dilution, the faster this will happen.

In the process of testing chemical preparations, the manufacturer empirically establishes the effective dose of a particular agent. When it decreases, efficiency decreases, which leads to the risk of resistance development in insect pests and pathogens. This is a very serious problem, and it is not without reason that strategies to prevent resistance have been developed for many years.

Ultra-low volume spraying – advantage or disadvantage?

The very idea of ultra-low volume spraying appeared in the eighties of the last century and at that time the instructions for the use of some chemicals indicated their effective doses for this method of application. However, over time this trend stopped. Drones were simply not available at that time, but it is possible that there are not so many such chemicals where this method proved to be efficient. Whatever the case, more safety and efficacy studies are needed for each crop protection chemical. Moreover, in the EU, such studies should be carried out by manufacturing companies and not agronomists. These studies need to be confirmed and indicate this method of application in the process of registration of the chemical, which presently does not seem to be the case.

Small droplet size – an advantage or a disadvantage?

There is another issue, which needs to be addressed. Agridrone sprayers advertise their advantages in producing ultra-fine droplets, almost a suspension, which, they claim, could help improve the efficiency of applying the chemicals.

However, these smaller-size droplets can also be easily carried by the wind to non-target areas. In hot weather, this suspension (or part of it) can evaporate before it reaches the surface of the leaves. Such things happen even when using traditional sprayers with larger droplets. As a result, the evaporated pesticide enters the clouds and subsequently falls out with precipitation. It could happen in the neighboring area, but also in the neighboring country. This is one of the reasons why organically certified products are, sometimes, contaminated with pesticides. Suspension can get into a cloud of fog and drift with it to neighboring fields, causing damage to cultivated plants for which this product is not intended.

The agronomist must remember all these risks when deciding on the use of an agridrone as a sprayer!

Agridrones are undoubtedly very promising for the release of entomophages  (insects and mites that destroy pests) in the open field. So far, they are used only for the release of Trichogramma, but only for now. There are more and more effective entomophages every year, and their use in the open field is hampered only by the lack of effective methods of release (sometimes they say ″evictions″).

Legal aspects

In a number of countries, aerial treatments for the use of plant protection products are prohibited. For example, in the EU this is possible only in strictly regulated cases in agreement with the relevant authorities. In Latvia, even the use of agricultural drones for the application of Trichogramma had to be coordinated with the State Plant Protection Service.

In some countries, the use of agricultural drones is not legally considered aerial processing, and in some countries the state does not yet regulate their use. However, this is an important point to be taken into account.