“Drift does not occur more or less in the south of the country, as it is not dependent on region, but rather on environmental and operational conditions…”
Vitor Araújo is a professor in the Department of Crop Science and Plant Health at the Federal University of Paraná – UFPR, an agronomist from UFV, with a M.Sc. and Ph.D in Agricultural Engineering from the State University of São Paulo.
Vitor Araújo, professor at UFPR
AgriBrasilis – What is agrochemical drift, and what causes it?
Vitor Araújo – Agrochemical spraying drift is the movement of sprayed droplets away from the target. It can occur either within or outside the application area. In the former case, it is termed endodrif, a natural phenomenon: as the sprayed area is not always fully covered by vegetation, particularly when the crop is in the early stages of its cycle. In the latter case, occurring outside the application area, it is termed exodrift. This is the most concerning type, as it can reach sensitive areas and cause damage to other crops, the environment, and even people.
The primary causes of drift are linked to incorrect decision-making at the time of application, specifically, the choice of an application technique with high drift potential combined with unfavorable environmental conditions. Generally, the recommended conditions for application are: temperatures below 30°C, relative humidity above 60%, and wind speeds between 3 and 10 km/h. Failure to follow these recommendations entails a high risk of losses due to drift.
The primary operational condition favoring the occurrence of drift is the use of fine-class droplets or smaller (< 218 µm).
AgriBrasilis – What damages can be caused by pesticide spraying drift?
Vitor Araújo – The damage caused by spray drift depends on the class of product used in the application. Herbicides can kill sensitive crops or damage native vegetation. Insecticides can cause mortality or sublethal effects in non-target organisms, such as pollinators and natural enemies. However, regardless of the product class, poisoning, to varying degrees, can occur in humans, animals, and the environment as a whole.
Drift also causes economic losses and can lead to regulatory consequences. From an economic standpoint, any product lost to drift fails to deposit on the target, potentially compromising control efficiency and increasing the need for re-applications.
In more critical situations, where drift occurs repeatedly due to a failure to adopt good agricultural practices, restrictive measures may be implemented at the municipal, state, or federal level to limit the use of specific chemical compounds, as happened with the herbicide 2,4-D in Rio Grande do Sul. In other words, improper use by some farmers can lead to restrictions that affect everyone, limiting access to important tools for weed management.
AgriBrasilis – Why does the South account for so many reports and conflicts involving drift?
Vitor Araújo – Drift is not dependent on the region itself, but rather on environmental and operational conditions determined by those directly handling the agrochemical application process. However, in recent years, we have seen numerous attempts to ban specific molecules. A major case occurred in Rio Grande do Sul involving “hormonal” herbicides (technically classified as auxin mimics), a category that includes 2,4-D, Dicamba, fluroxypyr, triclopyr, and others. Numerous instances of drift involving these herbicides were reported, causing damage to fruit crops in the state, such as grapes, apples, and nuts. The outcome was the creation of a normative instruction designed to tighten the requirements for applying these products.
Although drift is a phenomenon independent of geographic region, certain conditions in the South, such as the great diversity of crops and smaller farm sizes, make the agricultural environment more susceptible to conflicts arising from it. In the same region where fruit is grown, one also finds grains, forests, pastures, honey, and silk production; agrochemicals can travel short distances and affect crops or operations sensitive to them.
Another area of concern for the Southern region is the border shared with other countries, which facilitates the entry of illegal phytosanitary products; these may pose a significantly higher drift risk due to their formulation components.
AgriBrasilis – Why are hormone-based herbicides more frequently associated with drift damage?
Vitor Araújo – This is a generic name for the classification of herbicides belonging to Group O (auxin mimics) of the Herbicide Resistance Action Committee (HRAC). These products are commonly associated with drift, as they are frequently used to manage hard-to-control weeds, such as Conyza bonariensis (fleabane), particularly during desiccation operations. Consequently, the more a herbicide is used, the greater the risk of encountering problems associated with it.
However, fruit crops such as grapes are extremely sensitive to the acids found in these herbicides; consequently, even very low atmospheric concentrations can cause phytotoxic effects in vineyards. It is important to highlight that damage caused by drift stems primarily from the improper use of application technology, regardless of the specific molecules being sprayed.
AgriBrasilis – How can droplet drift be distinguished from volatilization, and what are the effects of a temperature inversion?
Vitor Araújo – In the field, it is virtually impossible to make this distinction unless experimental conditions are defined to clarify the matter. What I can say is that physical drift (caused by wind transporting the droplets) is extremely limited; in several studies I have conducted, it is not significant at distances greater than 200 meters from the sprayed area.
Vapor drift occurs due to droplet evaporation and/or the volatilization of the active ingredient; these can travel long distances and reach sensitive areas. This type of drift is intensified under thermal inversion conditions, where the finest droplets in the spray spectrum fail to deposit and remain suspended in the atmosphere, potentially evaporating and traveling long distances (exceeding 300 m). The resulting damage depends on the sensitivity of the targets to the drifted molecules; such damage is frequently associated with herbicides, as their effects are pronounced and visible in sensitive crops.
Close attention must be paid to thermal inversion conditions; the recommendation is to refrain from application and wait until weather conditions become favorable for application once again.
AgriBrasilis – What are the application technology recommendations for mitigating drift issues?
Vitor Araújo – Application technology recommendations for drift mitigation are known as Drift Reduction Techniques and operate through the integration of robust strategies. These strategies encompass operational and meteorological parameters, as well as spray mixture formulation.
Regarding operational parameters, the key factor in reducing drift is the selection of the appropriate spray nozzle, which is the primary component for increasing droplet size.
Regarding weather conditions, safety guidelines for application must be followed: temperatures below 30°C, relative humidity above 50%, and wind speeds between 3 and 10 km/h. These are reference values; the further the application conditions deviate from them, the greater the risk of drift.
Regarding the preparation of the spray mixture, the farmer should prioritize newer formulations containing drift-reducing co-formulants, as well as the use of drift-reducing adjuvants.
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