**3.2 Alternative spray technologies on soybean**

Nowadays, other technologies are available to the boom sprayers enabling higher spraying droplet canopy penetration in soybean culture. The difficulty in controlling Asian soybean rust and late season diseases has favoured the development of new spraying techniques, particularly due to the difficulty in reaching the exact target to be controlled. Thus, the use of the opener, rotating system nozzles, hose drops and electrification of droplets associated with air assistance can be mentioned.

#### **3.2.1 Opener**

Conventional sprayers linked to an artefact providing the canopy opener at the same spraying way can turn out to be an economic and effective alternative to soybean growers with lower purchasing power (Zhu et al., 2008b). These authors found that spraying performed with conventional sprayers linked to a canopy opener did not results significant differences in the coverage of the spray in the middle part of soybean plants when compared to spraying carried out using air assistance. However, the canopy opener coverage and air assistance along the bar was higher compared to treatments where the spraying was conducted by the conventional system without the canopy opener. Thus, the opener and spray boom coupling can provide deposition results similar to those obtained with the use of air assistance, besides being a more economical alternative to Asian soybean rust control (Figure 5). Considering the difficulties in controlling ASR by fungicide spraying, Prado (2011) evaluated the effectiveness of the canopy opener compared to conventional sprayers and air assistance in the spray boom on spraying deposition, rust control efficiency and soybean productivity. The experiment was conducted in a randomised block

Fig. 5. Canopy opener artefact fixed to the spray boom in a soybean crop.

especially in the first growth stages, by increasing the loss to soil proportionally to their size (Jorgensen & Witt, 1997). In vegetables, where droplet retention is limited by the presence of waxy layers on the cuticle, further studies are required, especially with air-assisted spraying, in order to evaluate the application quality (Koch, 1997). In the absence of vegetation (bare soil), air assistance may increase drift and deflect the air from the sprayer by the soil, unlike the effect which occurs in the presence of vegetation, with the impact of droplets on the leaf

Nowadays, other technologies are available to the boom sprayers enabling higher spraying droplet canopy penetration in soybean culture. The difficulty in controlling Asian soybean rust and late season diseases has favoured the development of new spraying techniques, particularly due to the difficulty in reaching the exact target to be controlled. Thus, the use of the opener, rotating system nozzles, hose drops and electrification of droplets associated

Conventional sprayers linked to an artefact providing the canopy opener at the same spraying way can turn out to be an economic and effective alternative to soybean growers with lower purchasing power (Zhu et al., 2008b). These authors found that spraying performed with conventional sprayers linked to a canopy opener did not results significant differences in the coverage of the spray in the middle part of soybean plants when compared to spraying carried out using air assistance. However, the canopy opener coverage and air assistance along the bar was higher compared to treatments where the spraying was conducted by the conventional system without the canopy opener. Thus, the opener and spray boom coupling can provide deposition results similar to those obtained with the use of air assistance, besides being a more economical alternative to Asian soybean rust control (Figure 5). Considering the difficulties in controlling ASR by fungicide spraying, Prado (2011) evaluated the effectiveness of the canopy opener compared to conventional sprayers and air assistance in the spray boom on spraying deposition, rust control efficiency and soybean productivity. The experiment was conducted in a randomised block

Fig. 5. Canopy opener artefact fixed to the spray boom in a soybean crop.

surface (Matthews, 2000).

**3.2.1 Opener** 

**3.2 Alternative spray technologies on soybean** 

with air assistance can be mentioned.

experimental design with six treatments: conventional spraying (T1), spraying with air assistance at maximum capacity of the fan rotation in the boom (T2), spray with a canopy opener to a depth of 0.10 m (T3), spraying with a canopy opener to a depth of 0.10 m with air assistance (T4), spraying with a canopy opener to a depth of 0.20 m (T5) spraying with a canopy opener to a depth of 0.20 m with air assistance (T6) and control treatment (without spraying) (T7) in four replicates, totalling 28 plots. The area of each plot was equivalent to 70 m2. The depths of 0.10 and 0.20 m refer to the distance from the canopy opener in relation to the top of the soybean plant. In addition to the distance between the canopy depth opener and the top of the plants, there is also a predetermined horizontal distance of 0.15 m between the boom and the canopy opener. The function of the canopy opener is to promote the soybean plants to slope forward, opening a space in the plant canopy and thus facilitating the flow, and consequently droplet deposition, on the bottom of the soybean plants. The sprayer used in the experiment was the Advance Vortex model 2000 with an 18.5 m long boom, 37 flat fan XR 8002 nozzles spaced 0.50 m apart operating at a pressure of 295 kPa and a spray volume of 150 L ha-1. The comparative effect of these different technologies on soybean productivity after three fungicide pyraclostrobin + epoxiconazole mixture sprayings at a dose of 25 + 66.5 g a.i ha-1 in the development stages R2, R3 and R5, as shown in Figure 6. The treatment T5 (spraying with a canopy opener at a depth of 0.20 m) had a higher productivity increase (54%) compared to control treatment. All treatments which received fungicide had significantly higher yields than the control treatment. There was no difference between the canopy opener and air assistance on soybean yield, making it an interesting and economical alternative for the control of Asian soybean rust. These results corroborate those obtained by Zhu et al. (2008).

Fig. 6. Effect of different treatments: conventional spraying (T1); air-assistance (T2); *canopy opener* at a depth of 0.10 m (T3); *canopy opener* at a depth of 0.10 m with air assistance (T4); *canopy opener* at a depth of 0.20 m (T5); *canopy opener* at a depth of 0.20 m with air assistance (T6) and treatment control (without spraying) on soybean yield.

#### **3.2.2 Rotating system nozzles**

Recently, the use of centrifugal energy to produce spray droplets (rotating system nozzle) is an interesting alternative application technology to control Asian soybean rust, using oily formulations, low spraying volumes and, consequently, a greater operational performance of sprayers. In Brazil, new techniques for pesticide application using low volumes and rotating nozzles have been developed in the mid-west region (Cerrado) for soybean rust control in soybean culture. The rotating nozzle low volume oily (LVO) and different levels of air speed with an air-assisted sprayer on spray deposits were compared by Christovam et al. (2010c) on Asian soybean rust control and soybean productivity. Two experiments were carried out in the experimental area of FCA/UNESP, Botucatu, SP, Brazil, on a soybean crop of the Conquista variety, in the 2007/2008 season. In the first experiment, three air levels (0, 9 and 29 km h-1 air speed generated by a fan) with flat fan XR 8002 nozzles and a spray volume of 130 L ha-1 were compared with a rotating nozzle – using LVO at 40 L ha-1 of spray volume (Figure 7). The second experiment was carried out under the same conditions as the previous experiment, including a control treatment (untreated plants). The grades varied between 0.6 and 78.5% disease severity. In general, air assistance promoted the increase on deposit levels on the adaxial surface of the leaf located in the top part of the plants. Therefore, in the bottom part, there was not a significant difference in spray deposits between the spraying techniques. Also, the abaxial surface did not show differences in deposit levels, in the top or bottom part, between the spraying techniques. The use of air assistance, when compared with the rotating nozzle system, did not show significant differences in spray deposits on adaxial or abaxial surfaces of the leaves in the bottom part of the plant. Monteiro (2006) observed results very similar to those obtained in the current study. This author performed a study that aimed to evaluate the spraying efficiency of a rotating atomiser system - LVO using 25 L ha-1 of fungicide outflow on a soybean crop, when compared to a sprayer equipped with hydraulic nozzles at a spray volume of 150 L ha-1. The treatments sprayed with the fungicidal mixture provided a weight of 1000 seeds and productivity significantly higher in comparison with untreated plants (control). The highest increase of productivity was obtained with the maximum air speed generated by the fan (29 km h-1) near to the spray boom using 130 L ha-1 when compared with the control treatment. The spray volume

Fig. 7. Spraying with an air-assisted sprayer and rotating system nozzles fixed at the spray boom on soybean culture.

applied with the rotating system nozzle – LVO was 40 L ha-1. Therefore, it did not provide the same increase in productivity compared with the treatment using air assistance at the maximum speed. The rotating system nozzle was 30% more economical than the treatment with a spray volume of 130 L ha-1, with or without air assistance near the boom, using the Advance Vortex 2000 sprayer.

#### **3.2.3 Hose drops**

132 Soybean Physiology and Biochemistry

Recently, the use of centrifugal energy to produce spray droplets (rotating system nozzle) is an interesting alternative application technology to control Asian soybean rust, using oily formulations, low spraying volumes and, consequently, a greater operational performance of sprayers. In Brazil, new techniques for pesticide application using low volumes and rotating nozzles have been developed in the mid-west region (Cerrado) for soybean rust control in soybean culture. The rotating nozzle low volume oily (LVO) and different levels of air speed with an air-assisted sprayer on spray deposits were compared by Christovam et al. (2010c) on Asian soybean rust control and soybean productivity. Two experiments were carried out in the experimental area of FCA/UNESP, Botucatu, SP, Brazil, on a soybean crop of the Conquista variety, in the 2007/2008 season. In the first experiment, three air levels (0, 9 and 29 km h-1 air speed generated by a fan) with flat fan XR 8002 nozzles and a spray volume of 130 L ha-1 were compared with a rotating nozzle – using LVO at 40 L ha-1 of spray volume (Figure 7). The second experiment was carried out under the same conditions as the previous experiment, including a control treatment (untreated plants). The grades varied between 0.6 and 78.5% disease severity. In general, air assistance promoted the increase on deposit levels on the adaxial surface of the leaf located in the top part of the plants. Therefore, in the bottom part, there was not a significant difference in spray deposits between the spraying techniques. Also, the abaxial surface did not show differences in deposit levels, in the top or bottom part, between the spraying techniques. The use of air assistance, when compared with the rotating nozzle system, did not show significant differences in spray deposits on adaxial or abaxial surfaces of the leaves in the bottom part of the plant. Monteiro (2006) observed results very similar to those obtained in the current study. This author performed a study that aimed to evaluate the spraying efficiency of a rotating atomiser system - LVO using 25 L ha-1 of fungicide outflow on a soybean crop, when compared to a sprayer equipped with hydraulic nozzles at a spray volume of 150 L ha-1. The treatments sprayed with the fungicidal mixture provided a weight of 1000 seeds and productivity significantly higher in comparison with untreated plants (control). The highest increase of productivity was obtained with the maximum air speed generated by the fan (29 km h-1) near to the spray boom using 130 L ha-1 when compared with the control treatment. The spray volume

Fig. 7. Spraying with an air-assisted sprayer and rotating system nozzles fixed at the spray

**3.2.2 Rotating system nozzles** 

boom on soybean culture.

Another possibility to improve spraying coverage with boom sprayers is addressed by spraying with three flat fan nozzles involving the entire planting row, of which two of them are positioned near the bottom of the plants or positioned on opposite sides between the crop rows and near the bottom of the plant. The structures that support the spray nozzle from the spray boom at its lower end are called hose drops. In the USA, there are several reports on the use of flat fan nozzles placed in the hose drops ends, which move in the line between the culture, with volumes around 140 L ha-1 in Asian soybean rust treatment (Ozkan, 2005), although their culture is planted at greater spacing than those in Brazil with early cultivars. In Brazil, growers with difficulty will adopt hose drops in this application in order to obtain better spray coverage of the leaves on the bottom part of soybean plants. However, the differences in the growth habits, foliage degree and plant architecture of the varieties and the smaller spacing between planting rows makes the use of this technology difficult.
