Assessment highlights benefits of spray adjuvants

Equipment calibration, choice of formulation and correct application of agricultural pesticides are factors that ensure efficient spraying in pest and disease control with low contamination to the environment and the operator.

The purpose of calibrating sprayers and spraying equipment is to check that they are as expected by the regulation, so that they can be used later. This procedure can be carried out simply by fine-tuning the working pressure. 

Calibration also involves diagnosing the condition of the tips. The system flow rate is checked, determining the application volume and the quantity of product to be placed in the tank. It is very common for operators to ignore the adjustment and only perform the calibration, which can cause significant losses of time and product.

To achieve maximum efficiency in controlling unwanted organisms, the factors mentioned above must be manipulated so that the applied solution fully reaches the desired target. Climatic factors, such as temperature, relative humidity and wind speed, must be monitored in order to choose the ideal time for application. 

In situations of high temperatures (above 30ºC), low humidity (below 50%) and strong winds (above 10km/h), wind speeds lower than 3km/h, the application of agricultural pesticides is also not recommended, as these conditions are conducive to evaporation and drift, thus altering the trajectory of the droplets in relation to the target. Therefore, applications should preferably be carried out in the early hours of the morning or at the end of the day. 

In order to increase the effectiveness and reduce the costs of phytosanitary treatment, adjuvants are added to the preparation of the mixtures, which alter the physical and chemical properties of the mixture, increasing wetting, the absorption of components by the leaves and reducing the formation of foam, at which point most of the active ingredients are wasted.

The addition of adjuvants to the spray mixture can alter the surface tension of the liquid, thus promoting changes in the spectrum of droplets formed. Droplets with a larger diameter have greater resistance to losses due to drift and evaporation, but can cause greater losses due to runoff. 

If the target to be controlled is located inside the canopy or on the underside of plant leaves, droplets with large diameters will have greater difficulty penetrating. On the other hand, droplets with a small diameter can reach the target.

Due to their smaller diameter and larger specific contact surface, smaller droplets are more susceptible to weather conditions, favoring losses due to evaporation and drift.

To better understand the effects of adjuvants, an experiment was carried out to test five products (adjuvants) mixed with water and only water as a control, four of which were silicone-based (Poliflex), (Naft), (TA35) and (Silkon) at a dose of 0,5 ml/L of spray, and another based on vegetable oil (Agr'óleo), at a dose of 0,5% of spray per hectare.  

For each treatment, two application volumes were used, 80 L/ha and 165 L/ha, and these applications were made with a centrifugal sprayer mounted on a nine-meter-long boom equipped with an electric motor. To evaluate the droplet spectrum, the sensitive paper labels were scanned and the images were processed using the Image Tool software, version 3.0.

Based on the analyses, some parameters were evaluated in each treatment, namely: the volumetric median diameter (VMD), which represents the diameter that divides a population of drops into two volumetrically equal halves; the homogeneity coefficient (CH), which the closer to 1 represents a more uniform droplet spectrum; the droplet density; the relative amplitude or Span, which also indicates the homogeneity of the spectrum; and the percentage of target coverage.

Under environmental conditions of temperature between 180C and 200C, relative air humidity between 45% and 58% and absence of wind, it was observed that there was no interaction between the volume and the product in the target coverage tests, since at 165L/ha the result reached 28,78% and at 80L/ha it reached 15,1%.

The homogeneity coefficient values ​​obtained were between 2,78 and 4,28 for the application volume of 165 L/ha and for the volume of 80 L/ha, the results ranged from 2,07 to 2,63. The Span ranged from 0,9775 to 1,2775 for the largest volume and 0,92 to 1,015 for the smallest.

As spray quality increases, greater homogeneity of the droplet spectrum must be required. It is necessary to analyze the VMD together with the relative amplitude to evaluate the effects of adjuvants in the spray, especially on the uniformity and distribution of the drops. 

The DMV values ​​ranged from 377,26μm to 594,50μm for 165L/ha, and from 287,73μm to 330,85μm for 80L/ha, as shown in Table 1. In the droplet density analysis, the result showed a trend directly proportional to the volume (Table 2), that is, the greater the spray volume, the greater the droplet density.

The droplet density provided by spraying with adjuvants is above the minimum density recommended for controlling diseases, insects and weeds. Therefore, by promoting larger droplets that are less susceptible to drift and evaporation, different formulations can influence spraying, improving quality and reducing environmental impacts on the crop and property.

The larger application volume used allowed greater target coverage. There was no significant difference in the coverage, DMV and droplet density results within each volume. The use of adjuvants in the spray mixture improved the droplet spectrum for spraying.

The means followed by the same capital letter in the row and lowercase letter in the column were statistically different from each other by the Tukey test at the 5% probability level. *(Witness) = Pure water.

The means followed by the same capital letter in the row and lowercase letter in the column were statistically different from each other by the Tukey test at the 5% probability level. *(Witness) = Pure water.

*Per Tiago Mencaroni Guazzelli, Marconi Ribeiro Furtado Junior, Victor de Souza Lopes e Paulo Roberto Forastiere, from UFV, and Humberto Santiago, from Ufob