Assessing herbicide symptoms by using a logarithmic field sprayer

In field experiments, assessment of herbicide selectivity and efficacy rarely takes advantage of dose-response regressions. The objective is to demonstrate that logarithmic sprayers, which automatically make a logarithmic dilution of a herbicide rate, can extract biologically relevant parameters describing the efficacy of herbicides in crops, and compare localities and time of assessment.

In a conventional and an organic field, canola, white mustard, and no crop plots were sprayed with diflufenican and beflubutamid. A mixed effect log-logistic dose-response regression, with autoregressive correlation structure, estimated ED₅₀ and ED₉₀ for visual and Excess Green Index symptoms at various days after treatment (DAT). For visual assessment, ED₅₀ differed within no crop between locations for beflubutamid at 12 DAT and 26 DAT. For diflufenican, the ED₅₀ was different within crops at the two fields at 12 DAT, but not at 26 DAT. The Excess Green Indices at ED₅₀ were not different among herbicides, locations, and corps; ED₉₀ differed for white mustard and canola for beflubutamid but not for diflufenican.

Suitable nonlinear regression models are now available for fitting dose-response data from a logarithmic sprayer in field experiments. The derived parameters (e.g. ED₅₀ ) can compare selectivity and efficacy at numerous cropping systems. © 2018 Society of Chemical Industry.