Herbicide coverage in narrow row soybean as influenced by spray nozzle design and carrier volume

The use of reduced drift nozzles that produce larger droplet sizes that are less prone to drift will likely be required for use of future postemergence herbicide applications in soybean in the USA. Experiments to evaluate the effect of reduced drift spray nozzles on spray solution coverage were conducted in the field in Indiana. Air induction extended range (AIXR) and turbo TeeJet air induction (TTI) nozzles that produce extremely coarse to ultra coarse droplets were compared to extended range (XR) and Turbo TeeJet (TT) nozzle that produced fine to coarse droplets. Each nozzle was evaluated for spray coverage at 94 and 140 l ha^-1 spray volumes using water sensitive cards. Precipitation varied between site years and resulted in differences in soybean canopy development and spray solution coverage. Coverage was greater at the top of the canopy than at the bottom of the soybean canopy as expected. An interaction occurred at the top and middle of the canopy in which the AIXR and TTI nozzles had similar coverage between the two spray volumes, whereas the XR and TT nozzles had greater coverage at 140 l ha^-1 carrier volume than 94 l ha^-1 carrier spray volume. Spray solution coverage at the bottom of the canopy, where target weeds would be, was similar between all nozzle types. Coverage was greater at the bottom of the canopy at 140 l ha^-1 spray volume than with the 94 l ha^-1 carrier volume. Spray volume has a greater influence on coverage than spray nozzle type and AIXR and TTI nozzles are less prone to coverage differences due to spray volume than the XR and TT nozzles.