Assessing herbicide symptoms by using a logarithmic field sprayer.

Background: 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.
Results: 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 ED ₅₀ and ED ₉₀ for visual and Excess Green Index symptoms at various days after treatment (DAT). For visual assessment, ED ₅₀ differed within no crop between locations for beflubutamid at 12 DAT and 26 DAT. For diflufenican, the ED ₅₀ was different within crops at the two fields at 12 DAT, but not at 26 DAT. The Excess Green Indices at ED ₅₀ were not different among herbicides, locations, and corps; ED ₉₀ differed for white mustard and canola for beflubutamid but not for diflufenican.
Conclusion: Suitable nonlinear regression models are now available for fitting dose-response data from a logarithmic sprayer in field experiments. The derived parameters (e.g. ED ₅₀ ) can compare selectivity and efficacy at numerous cropping systems. © 2018 Society of Chemical Industry.
(© 2018 Society of Chemical Industry.)