The effects of spray application rate and droplet size on applications to control soybean rust

Abstract

Canopy penetration and thorough coverage are important when applying foliar fungicides to soybeans for the control of rust. The purpose of this study was to examine how spray application rate and spray droplet size affect the efficacy of soybean rust applications. Four treatments were examined: a medium droplet spectrum applied at 47 L/ha (5 GPA) and at 140 L/ha (15 GPA), and a very coarse droplet spectrum applied at 47 L/ha (5 GPA) and at 140 L/ha (15 GPA). Applications were made to soybeans planted with 91 cm (36 inch) row spacing in the R5 growth stage. Spray coverage, deposition, soybean rust severity, and yield were measured to evaluate the effectiveness of these treatments. Spray coverage was measured on Kromekote paper positioned in the upper and lower parts of the canopy. Deposition was measured using a dye and Mylar plates positioned in the upper and lower parts of the canopy. The very coarse droplet spectrum at 140 L/ha (15 GPA) had the highest coverage and deposition in both the upper and lower canopy. Overall the very coarse droplet spectrum performed better than the medium droplet spectrum. There was no difference among the treatments in soybean rust severity or yield. All the treatments had significantly lower soybean rust severity than an untreated control, and all but the very coarse droplet spectrum at 140 L/ha (15 GPA) had a significantly higher yield than the untreated control.

Spray droplet spectrum and spray deposition in different soybean sowing systems

“…Such results agree with Bretthauer et al (2008), who verified a reduction of 12.1% in the MVD from the higher to the lower part when evaluating the spectrum of medium and thick droplets. Two other studies looked for answers on this subject: Yu et al (2009) confirmed influence of relative humidity on the droplet size reduction, which was 10 times faster when comparing droplets with 246μm and 800μm with 60% of relative humidity and reduction of MVD in the middle and lower part of the canopy.…”

Espectro de gotas de pulverização e controle da ferrugem-asiática-da-soja em cultivares com diferentes arquiteturas de planta

“…Nas três aplicações, foi verificada redução no DMV do terço superior para o inferior (Tabela 1). Bretthauer et al (2008), ao avaliar espectro de gotas médio e muito grosso para controle de ferrugem-asiática-da-soja, relataram que o DMV na porção inferior das plantas diminuía, em média, 12,6 e 11,6%, respectivamente.…”

An automated nozzle controller for self-propelled sprayers

“…Ozkan et al (2006) found medium droplet sizes resulted in greater coverage in the lower and middle portions of dense canopies of soybeans when compared to fine and coarse droplets. Bretthauer et al (2008) similarly observed greater control of soybean rust with very course droplet sizes. Hanna et al (2006), Prokop and Veverka (2006), and Derksen et al (2001) did not find droplet size to be a significant factor influencing efficacy of fungicides.…”

“…Insecticide function relies on coverage of the plant for protection against pests. While coverage is higher in the upper canopy for smaller droplet sizes, penetration into the lower portions of the canopy is minimal (Bretthauer et al, 2008;Ozkan et al, 2006). A balance between small droplets for increased coverage and large droplets for increased penetration is achieved at the medium droplet size.…”

“…Research concludes that contact fungicide efficacy, similar to insecticide efficacy, is optimized when medium droplets (200 m-350 m) are applied (Bretthauer et al, 2008;Ozkan et al, 2006). These droplets have the ideal size to produce coverage in all sections of the canopy.…”