Spray evaporation: what to do when it happens?

Spray evaporation, and spray drift, can occur during the phytosanitary products application process. In other words, the agricultural pesticide is lost because it does not reach the target. After it occurs, nothing can be done; product, operational efficiency, time, and resources are lost. Additionally, it causes environmental impacts to other sensitive non-targetted areas, and user intoxication. Therefore, the best route is to reduce this problem.

Several factors can raise the chances of evaporation, and some strategies help reduce this loss. Continue reading this post and stay on top of it!

Why does spray evaporation happen?

Spraying consists of breaking the liquid (or syrup) into small drops. In some cases, the drops need to have a minimal size because the target (disease or plague) is well hidden somewhere in the plant.

Depending on the environmental conditions related to temperature and relative humidity, these drops evaporate completely at some point between the spray nozzle and the target.

So, as a rule, the smaller the drop, the faster the loss of speed after the nozzle produces it, and it can easily get suspended in the air and more quickly evaporate. There is a greater chance of depositing the product on the target with larger drops, but these drops have greater limitations when it comes to finding most hidden targets, and thus promotes lower surface coverage.

This occurs independently of the technology used, and is favoured with inadequate environmental conditions such as high temperature and reduced relative humidity. In addition, some specific phytosanitary products may be more subject to evaporation than others.

The air currents also affect this phenomenon, acting on the drift and the potential drops evaporation since the distance to the deposit site increases. Since the size of the drops is reduced, they are more vulnerable to air movement, either in horizontal currents (wind) or in vertical currents (convection).

After evaporation, the active ingredient is suspended and can be carried considerable distances, according to the strength of the wind. This creates damage to water resources, plants sensitive to the product and people’s health.

What are the best practices for reducing spray evaporation?

It is essential to use the best methods, technologies, and knowledge to reduce spray droplets evaporation as much as possible, ensuring greater operational efficiency, environmental and operator protection. Here’s how to do that.

Spray calibration

To minimize this evaporation, you first need to work with an optimal application volume for that crop at that time—so calibration is essential. Here, several aspects should be considered.

Boom height

Remember that the greater the distance between the boom and the ground, the greater the chances of the drops evaporating on the path, besides favouring the occurrence of drift. The shorter this distance, the lower the probability of these losses happening. The solution is not only to lower the boom because adjusting this without considering the nozzles can generate an irregular spray range, leaving areas untreated.

When lowering the boom, use higher angle tips (110°). Always make sure that the spray range is being formed properly. In general, the boom height should be sufficient for a double-crossing of the jets to be observed. For nozzles with the 110° angle, the ideal boom height is equal to the spacing between the nozzles.

Spray pressure

Pressure is the force that controls the output velocity of the liquid from the nozzles. When it collides with the air, this liquid breaks into drops. The higher the pressure, the smaller the drops and the higher the evaporation probability:

• drops smaller than 50 micrometres will evaporate in a few seconds under various environmental conditions;
• drops between 50 and 200 micrometres can evaporate, depending on the conditions of the environment.

Thus, it is important to work with a pressure recommended by the manufacturer — usually in the range of 30 to 50 psi for conventional flat jet tips, also known as fan type nozzles.

Spray nozzles

The spray nozzle can also determine the drop size. Dozens of models can produce a wide variety of diameters, from 25 micrometres to 1 mm. In general, the quality of the tips is defined according to the uniformity of the drops produced. It is more difficult to produce more uniformly sized drops.

Assessment of environmental conditions

We should also consider the environment’s temperature and humidity. You can, for example, choose times that minimize evaporation. Of course, it is not the time itself that interferes with evaporation but the climatic conditions derived from that period of the day. Hence, depending on the temperature, humidity and drop size, one reaches an evaporation rate.

Another important aspect concerning the schedule is that at higher temperatures of the day, the plant tends to stand more upright, facilitating the deposition of products. On the other hand, this heat makes the operation more susceptible to evaporation. So, the rule is: the higher the relative humidity of the air, the thinner the drop can be. When it is scorched and hot, thicker drops should be used and, to ensure good target coverage, increasing the application volume may be necessary. The farmer must understand this dynamic well.

There are regions where the temperature is no longer favourable for spraying early in the morning, exceeding the recommended maximum of 30 degrees. So, more than paying attention to the schedule, it is important to evaluate the environmental conditions.

Therefore, it is ideal to use appropriate tools to measure this quality and apply it in future operations. Some machines can generate a map of the potential of evaporation in real-time through telemetry, for example. The sensors collect data on temperature and humidity and the selection of drops applied at that time.

With this precision agricultural information and crop damage and productivity agent control maps, you can ensure that spraying is within standards. Telemetry reports from machines generate valuable data for the farmer to improve their processes and reduce problems such as spray evaporation.

Adjuvants

Although climate, application volume and drop size are important factors to consider when avoiding spray evaporation, adjuvants can greatly improve operation. Adhesive agents, for example, are made from oil or silicone to fix onto the leaf surface and prevent evaporation. They are indicated for different situations, according to their recommendations.

Remember that spray evaporation is an invisible and real risk, which can profoundly impact the quality of your operation. In addition, there is a type of drift that can generate environmental risks, and health risks for your workers. Therefore, always ensure best practices to achieve satisfactory results.

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