Impact of imazamox containing herbicides on the development of resistance in black-grass (Alopecurus myosuroides Huds.)

Abstract

Winter oilseed-rape was the most common crop in Western Europe where no ALS-inhibitor was used. Due to the introduction of Clearfield winter oilseed-rape varieties the use of ALS-inhibitors also in oilseed-rape is possible. If the broader use of ALS-inhibitors increases the selection pressure on herbicide resistant weeds and increases their occurrence in the crop rotation is the question of this investigation. Therefore, an outdoor container trial (á 350 l, 0.7 m²) was performed starting in autumn 2011. A typical crop rotation of winter wheat/oilseed-rape/winter wheat was simulated in the following three years. Three different black-grass biotypes with characterised resistance pattern and 5 different herbicide programs were analysed. The blackgrass biotypes showed different target-site resistance against ACCase- and/or ALS-inhibitor, as well as metabolic resistance. Before and after each treatment the numbers of black-grass plants per container were counted. Also the numbers of heads were counted before harvest. Additionally genetic analysis due to PCRs and pyrosequencing of ten survivors per container and year were performed. Till now results of the winter wheat and oilseed-rape cultivation were obtained. Herbicide efficacy was between 77 and 98% for the treatments during the winter wheat cultivation. The genetic analysis showed nearly similar portion of TSR in the black-grass populations when compared with the initial frequencies. Only one container showed no TSR. The comparison of the herbicide programs sprayed during the oilseed-rape cultivation showed the best results for all black-grass biotypes for the application of: Metazachlor + dimethenamid (BBCH 09/10), imazamox + quinmerac + Dash (BBCH 14) and propyzamide (BBCH 21/22)