Bioassay Development for the Identification of Pre-emergence Herbicide Resistance in Alopecurus myosuroides (Huds.) Populations | Entwicklung eines Biotest zur Prüfung von Herbizidresistenzen gegenüber Vorauflauf Herbizide bei Ackerfuchsschwanz (Alopecurus myosuroides Huds.) Populationen

Herbicide-resistant Alopecurus myosuroides (Huds.) is an increasing problem in winter wheat in Western Europe. An increasing number of farmers need sequential herbicide applications to control biotypes with non-target-site resistance. Pre-emergence herbicides play an important and increasing role in resistance management. However, cases of pre-emergence herbicide resistance due to non-target-site mechanisms occur. This paper presents the results of bioassays to determine a reliable standard protocol for the diagnosis of resistance to pre-emergence herbicides in A. myosuroides. Testing was conducted to determine the influence on herbicide efficacy of two different soil types and three kinds of seed coverage, as well as analyses of the optimal assessment date. Additionally, dose-response experiments in soil-based pot bioassays under two growth conditions with pre-germinated seeds and a confirmatory field trial were carried out. Four different herbicides belonging to the HRAC-groups N, K₃, and C₂ were analysed (prosulfocarb, flufenacet, chlorotoluron, and metazachlor). The data showed no statistical influence of sandy loam or a mixture of sandy loam with sand as soil to the differentiation between susceptible and resistant biotypes. The seed coverage influenced the herbicide efficacy. Reliable results for all herbicides within the soil-based pot bioassay under greenhouse conditions at specific assessment dates were obtained. Suggested discriminating rates are 2000 g a.i. ha⁻¹ for prosulfocarb (dat 14), 75 g a.i. ha⁻¹ for metazachlor (dat 14), 2100 g a.i. ha⁻¹ for chlorotoluron (dat 28), and 125 g a.i. ha⁻¹ for flufenacet (dat 14). The pot assay was shown to be an appropriate procedure for the identification of pre-emergence herbicide resistance to prosulfocarb, metazachlor, chlorotoluron, and flufenacet in A. myosuroides. Consequently, a reliable, quick, and easy to handle bioassay which is required for high throughput screening was detected in the present study.