Acetochlor [HRP]

Trifluralin and acetochlor are two nitrogen-containing current use herbicides. While both herbicides have been observed in the atmosphere and have the potential to undergo atmospheric oxidation before deposition to off-target areas, the atmospheric photooxidation chemistry of these species is poorly understood. We use an oxidative flow reactor to expose the two herbicides to increasing concentrations of OH radicals, detecting pesticides and products using an iodide chemical ionization mass spectrometer. We identify new oxidation products and propose photooxidation mechanisms for trifluralin and acetochlor. Both herbicides contain reduced organic nitrogen atoms, and their OH oxidation produces isocyanic acid. While aerosol was observed in the flow reactor only for acetochlor, our results indicate that OH oxidation of neither herbicide would contribute to secondary organic aerosol formation under typical ambient atmospheric conditions. However, high wall losses of both pesticides in the flow reactor suggests that partitioning to pre-existing aerosol may occur and enable subsequent transport in the atmosphere.

A small plot field trial with Roundup Ready maize was carried out in the central part of Bohemia to a) compare the efficacy of various glyphosate treatments with conventional herbicides, b) describe the sensitivity of selected weeds to glyphosate, and c) evaluate the differences in weed biomass production under various herbicide treatments. Best herbicide efficacy was provided by a split application of glyphosate (1080 + 1080 g ad ha(-1).) and a tank-mix combination of glyphosate + acetochlor (1080 + 2100g a.i. ha(-1)). However, obtained efficacy did not differ significantly from the efficacy of pre-mergence herbicides in most species. The most sensitive species to glyphosate was Amaranthus retroflexus L. (ED90 = 412 g a.i. ha(-1)) followed by Solanum physalifolium Rusby (475 g a.i. ha(-1)), Chenopodium album L. (677 g a.i. ha(-1)), Mercurialis annua L. (685 g a.i. ha(-1)), and Echinochloa crus-galli (L.) PB. (1335 g ad. ha(-1)). The highest suppression of the weed biomass (98.6% and 99.4% of control plot) and the highest maize yield (increase of 711-1809 kg ha(-1) compared to pre-emergence herbicides) was found in treatments with Roundup Ready herbicide.