**3.2.4 Electric charge (electrostatic) in spray droplets**

Nowadays, air assistance can be combined with electrification (by induction) of the spraying droplets, aiming at reducing drift and exposure of appliers and the environment to phytosanitary products. An experiment was carried out in commercial areas of the soybean crop, Cidade Verde Farming, Primavera do Leste, MT, Brazil, on soybean plants of the Monsoy 8757 variety in the 2009/2010 agricultural season. Sowing was performed in 12/11/2009, leaving 0.45 m spacing between planting rows and 14 seeds per linear metre. The experimental design was in random blocks, with six treatments constituting three application techniques: conventional spraying, air-assisted spraying and air-assisted spraying combined with electrically charged droplets in two spray volumes, 50 and 100 L ha-1, in four replications, totalling 24 experimental plots. The experimental plots were 24.0 x 100.0 m (width x length). The width of the plots corresponded to the boom size of the sprayer used in this research. During spraying, a self-propelling sprayer (Uniport 3000 model) was used equipped with a spray boom 24.0 m in length with hollow conical nozzles spaced every 0.35 m. The spray hollow conical nozzles used were of the JA-1 and JA-2 type, operated at working pressures of 690 and 828 kPa respectively. The spray displacement speed was 15 km h-1, usually practiced by farmers in the Brazilian mid-western region (Cerrado). This sprayer operated with or without air assistance on the spray boom (conventional) combined with electric charge transference to the spray droplets in turn-on or turn-off mode. For air supply into the sleeve boom, two axial fans were positioned on the central point of the boom and operated at the maximum rotation speed. For the quantification of spray deposits, a tracer dye (Brilliant Blue) was used at a concentration of 0.3%, according to qualitative and quantitative evaluation studies of spray deposits validated by Palladini et al. (2005). The spraying of the tracer dye was performed in the R5.1 growth stage, 80 days after sowing. The average values of height and foliar area were respectively 0.92 m and 0.158 m2 at this growth stage. The mean values of spray deposits with different application technologies on soybean plants of the Monsoy 8757 variety are shown in Tables 4 and 5. Greater spray deposits were obtained with air assistance and this spray technology combined with electrically charged droplets in relation to conventional spraying at 100 L ha-1 on leaflets positioned at the top part of soybean plants (Table 4). At a low volume rate, there was no observed difference in deposit levels with the different spray technologies. With the higher spray volume using air assistance combined with electric charge transference to the droplets, it was possible obtain greater spray deposits when compared to low spray volume. The best spray deposits on leaflets at the bottom position of soybean plants was obtained with air assistance combined with electric charge transference technology at a volume of 100 L ha-1 (Table 5). With this spray volume, air assistance technology combined with electrically charged droplets was better when compared the other two spraying technologies. There was no significant difference between the spraying techniques on tracer deposits using the volume of 50 L ha-1 (Table 5). These results obtained with a new spray technology, employing air assistance combined with electric charge transference to droplets, is very promising in disease management in this culture, especially for Asian soybean rust management.


Original means and data transformed in root square of x + 0.5 for analysis. Means followed by the same letter, smaller in the column and bigger in the line, did not differ by Tukey's test at the 5% significance level.

Table 4. Mean values of Brilliant Blue tracer deposits (µL cm-2) on leaflets at the top position of soybean plants after spraying with different techniques. Botucatu, SP, Brazil, 2009/10.


Original means and data transformed in root square of x + 0.5 for analysis. Means followed by the same letter, smaller in the column and bigger in the line, did not differ by Tukey's test at the 5% significance level.

Table 5. Mean values of Brilliant Blue tracer deposits (µL cm-2) on leaflets at the bottom position of soybean plants after spraying with different techniques. Botucatu, SP, Brazil, 2009/10.

#### **4. Considerations of ASR management**

Despite new techniques and equipment available for the application of fungicides targeting Asian soybean rust management, other factors such as climate conditions, varieties, disease severity, plant architecture, fungicide characteristics, sowing in the same season and application time are important in ensuring culture productivity. Associated with chemical control, plant disease resistance and the adoption of the period of sowing interruption (inter-season) in most Brazilian states have contributed to decreasing the severity of Asian soybean rust. Disease monitoring time of application and choice of fungicide are important factors for the success of Asian soybean rust control. Beforehand sowing and choosing an early variety can also contribute to the control of this disease. Nowadays, multidisciplinary research development is necessary to achieve suitable management of Asian soybean rust. Only knowledge of pesticide application techniques is not sufficient to improve control of the *P. pachyrhizi* pathogen.

#### **5. References**

134 Soybean Physiology and Biochemistry

spray deposits with different application technologies on soybean plants of the Monsoy 8757 variety are shown in Tables 4 and 5. Greater spray deposits were obtained with air assistance and this spray technology combined with electrically charged droplets in relation to conventional spraying at 100 L ha-1 on leaflets positioned at the top part of soybean plants (Table 4). At a low volume rate, there was no observed difference in deposit levels with the different spray technologies. With the higher spray volume using air assistance combined with electric charge transference to the droplets, it was possible obtain greater spray deposits when compared to low spray volume. The best spray deposits on leaflets at the bottom position of soybean plants was obtained with air assistance combined with electric charge transference technology at a volume of 100 L ha-1 (Table 5). With this spray volume, air assistance technology combined with electrically charged droplets was better when compared the other two spraying technologies. There was no significant difference between the spraying techniques on tracer deposits using the volume of 50 L ha-1 (Table 5). These results obtained with a new spray technology, employing air assistance combined with electric charge transference to droplets, is very promising in disease management in this culture, especially

**Spray technique Volume (L ha-1) LSD values** 

Air-assistance 0.684 Aa 0.480 Aa 0.350

Table 4. Mean values of Brilliant Blue tracer deposits (µL cm-2) on leaflets at the top position of soybean plants after spraying with different techniques. Botucatu, SP, Brazil, 2009/10.

**Spray technique Volume (L ha-1) LSD values** 

Air-assistance 0.215 Ab 0.029 Aa 0.622

Table 5. Mean values of Brilliant Blue tracer deposits (µL cm-2) on leaflets at the bottom position of soybean plants after spraying with different techniques. Botucatu, SP, Brazil,

charge 0.744 Aa 0.352 Ba

**CV (%)** 11.27

Means followed by the same letter, smaller in the column and bigger in the line, did not

Conventional 0.254 Ab 0.313 Aa

Original means and data transformed in root square of x + 0.5 for analysis.

electric charge 1.166 Aa 0.016 Ba

Conventional 0.033 Ab 0.115 Aa

**CV (%)** 21.11 Original means and data transformed in root square of x + 0.5 for analysis.

Means followed by the same letter, smaller in the column and bigger in the line, did not

**LSD values (p< 0.05)** 0.758

differ by Tukey's test at the 5% significance level.

**LSD values (p< 0.05)** 0.427

differ by Tukey's test at the 5% significance level.

**100 50 (p< 0.05)** 

**100 50 (p< 0.05)** 

for Asian soybean rust management.

Air-assistance + electric

Air-assistance +

2009/10.


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