ARS | Publication request: Dispersion and evaporation of droplets amended with adjuvants on soybeans

Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 20, 2012
Publication Date: January 20, 2013
Citation: Gimenes, M., Zhu, H., Raetano, C., Oliveira, R. 2013. Dispersion and evaporation of droplets amended with adjuvants on soybeans. Crop Protection Journal. 44:84-90.

Interpretive Summary: Soybeans are often susceptible to insect infestations and to diseases that cause significant yield losses. Protective pesticide spray applications on soybeans can increase yield and quality, but they also increase production costs which can be ameliorated with less spray mixtures and minimized off-target loss. The effects of four different groups of adjuvants at various concentrations on dispersion and evaporation of single droplets at four targeted soybean plant surfaces (adaxial and abaxial surfaces of leaflet, petiole of leaflet, and basal stem) were investigated under controlled conditions. A single-droplet generator was used to produce and deposit desired-size droplets on target surfaces. This systematic investigation precisely demonstrated that adjuvant-amended foliar sprays increased the coverage area on soybean plants by over 400% which is a fourfold reduction in spray volume. The use of adjuvants also improved the homogeneity of sprayed pesticides. These findings provide convincing evidence to growers that they can potentially reduce significant amounts of spray mixtures by using adjuvants to increase droplet dispersion on soybean plants, resulting in reduced soybean production cost and also reduced environmental contamination.

Technical Abstract: Increased use of adjuvants to improve pesticide spray application efficiency is hindered by a lack of knowledge to enhance droplet adhesion. Dispersion and evaporation of single 300 µm droplets amended with four different spray adjuvants deposited at four different soybean plant locations were investigated. The locations included the abaxial and adaxial leaflet surfaces, the petiole and the basal stem. The four adjuvants in spray mixtures were crop oil concentrate (COC), modified seed oil (MSO), nonionic surfactant (NIS), and oil surfactant blend (OSB). Five concentrations of each adjuvant were used to prepare the spray mixtures. A single-droplet generator produced and deposited droplets on target surfaces at 60% relative humidity and 25°C ambient temperature. As a control, water-only droplets also were tested. Adjuvants COC, MSO, NIS, and OSB in spray mixtures significantly increased the dispersion area (or wetted area) of droplets at the soybean plant surfaces. Droplet dispersion did not increase linearly with increased adjuvant concentrations. The average increase of droplet wetted areas at four soybean plant surfaces was 443% when the spray mixture was amended with 1.04% (v/v) of COC. The largest wetted area was on the abaxial leaflet surface, followed by adaxial surface, petiole and then the basal stem. Droplet evaporation times were inversely proportion to droplet wetted area. The evaporation time of 300 µm diameter droplets ranged from 36 to 142 s on the four soybean plant surfaces when the spray mixture was amended with one of the four adjuvants while water-only droplets ranged from 161 to 190 s. The use of adjuvants offered great potential to improve the homogeneity of sprayed pesticides, increase spray coverage area on soybean plants, reduce pesticide application rates, benefit the farmer economically, and reduce environmental contaminations by pesticides.