Abstract
ABSTRACT Maintaining homogeneity in the distribution of fungicidal sprays applied throughout the plant, minimizing the variation between the upper and lower third of the plant, is one of the main challenges for application technologies with regard to soybean crops. To increase the deposition and leaf coverage of sprayed compounds, especially in the middle and lower thirds of the plant, we developed and tested alternative assisted boom sprayer systems. In this study, three assisted boom sprayer systems (Vortex®, Dropleg®, and chain curtain) were evaluated, in addition to the conventional system, in terms of the deposition and coverage of the leaf surface they achieved in the upper, middle, and lower thirds of plants using the fluorescent tracer Helios SC 500™. The assisted boom sprayer systems allowed the sprayed mixture to be better distributed throughout the plant. With the conventional spray system (without assitance), the deposition in the upper third was approximately 26 times higher than that in the lower third, whereas with the use of the assisted boom sprayer systems, the difference in deposition between these thirds was 11 times higher. Among the evaluated systems, the Dropleg® system presented the lowest depositional variation, which was only 5.5 times higher in the upper than in the lower third, because of the increased deposition achieved in the lower third of the plant. Leaf coverage varied from 41% to 81% in the upper third, from 24% to 43% in the middle third, and from 4% to 13% in the lower third of the plant. Using the conventional spray system, the leaf surface coverage was approximately 13 times higher in the upper third than in the lower third of the plant, whereas with the use of the assisted boom sprayer systems, especially the Dropleg® system, this variation was reduced by 73%, and the coverage of the upper and lower thirds only differed by 3.5 times. Indeed, the Dropleg® system reached a leaf coverage of close to 13% in the lower third of the plant. The use of assisted boom sprayer systems improved the distribution of the mixture applied throughout the plant, reducing the differences among the thirds of the plant both in the levels of deposition and coverage of the leaf surfaces. The Dropleg® system increased the deposition and leaf coverage in the lower third of the plant the most, facilitating better distribution of the mixture.
Highlights
Many factors can depreciate the productivity of soybean crops, including pests and diseases, which means that management actions are needed, including the use of pesticides
The deposition and leaf surface coverage of an applied mixture achieved by three different assisted boom sprayer systems were evaluated: the Vortex®, Dropleg®, and the chain curtain systems; the deposition and coverage achieved by the conventional spray system without the use of assisted mechanisms were evaluated (Table 1)
The chain curtain system resulted in similar deposition in the upper thirds of the plants (3.72 ± 0.35 ng cm-2/g ha-1) to the Vortex® system, and achieved higher deposition than the Dropleg® system by up to 34% (Figure 1)
Summary
Many factors can depreciate the productivity of soybean crops, including pests and diseases, which means that management actions are needed, including the use of pesticides. Conventional spray techniques using hydraulic or centrifugal nozzles, regardless of the application volume, provide low deposition and coverage in the middle and lower thirds of the plant, especially in plants with high leaf areas like soybean, causing the applied products to have low efficiency Graziano et al, 2017; Roehrig et al, 2018; Müller et al, 2018) This has negative impacts on pest and disease management, as the evolution or development of these problems proceeds from the lower portion of the plant towards the apex, between which the variations in the coverage of the leaf surface by applied pesticides can be as high as twenty-three times (Roehrig et al, 2018). As the plants grow, the concentration of the droplets increases at the top of the canopy relative to that at the lower and middle parts of the plant
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