Browsing by Subject "Herbizidresistenz"

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Incorporating agronomic measures into integrated weed management strategies using pre-emergence herbicide cinmethylin to control Alopecurus myosuroides Huds.
(2022) Messelhäuser, Miriam; Gerhards, Roland
Alopecurus myosuroides Huds. is one of the most problematic grass weeds in cereal production in Western Europe. This grass weed spread rapidly due to the repeated and intensive use of herbicides with the same mode of action and changes in arable cropping and tillage systems. Herbicide applications are the common agricultural practice for successful control of A. myosuroides due to its high flexibility and low cost. However, due to European and national restrictions and the growth of herbicide-resistant populations, farmers are forced to reduce herbicide use to minimize chemical impacts on the environment and food chain. As a holistic approach for reducing herbicide use, integrated weed management (IWM) is a diversification of the control strategy of A. myosuroides. In this thesis, several aspects of IWM were examined and combined to test for a successful A. myosuroides control strategy in winter cereals. Special attention was paid to cinmethylin, a pre-emergence herbicide with a new mode of action in winter cereals to control A. myosuroides. The first article comprised the development of an agar bioassay sensitivity test to determine sensitivity differences in A. myosuroides populations to pre-emergence herbicides containing flufenacet and the re-discovered substance cinmethylin. All of the tested populations did not show reduced sensitivity to cinmethylin, but differences in resistance factors were observed between the agar bioassay sensitivity test and the standard whole plant pot bioassay in the greenhouse. Nevertheless, it was possible for the most part to confirm the results for cinmethylin and flufenacet of the standardized greenhouse whole plant pot bioassay in the agar bioassay sensitivity tests and hence create a reliable, faster test system. The second article focused on cultural measures like cover crop mixtures, various stubble tillage methods and glyphosate treatments and their effect on total weed infestation in particular on A. mysouroides and volunteer wheat. Within two field experiments, the cover crop mixtures and the dual glyphosate application achieved a control efficacy of A. myosuroides of up to 100%, whereas stubble tillage and the single glyphosate treatment did not reduce A. myosuroides population significantly. The results demonstrated, that besides a double glyphosate application, well developed cover crop mixtures have a great ability for weed control, even for A. myosuroides. The third article also dealed with the combination of cultural measures (delayed seeding) and herbicide application and their influence on A. myosuroides control efficacy and yield response of winter wheat and triticale. Results indicate that cultural methods such as delayed seeding can reduce A. myosuroides populations up to 75%, although to achieve control efficacy of > 95%, supplementary herbicides should be used. In the fourth article, a two-year experiment on two experimental sites was set up with a special focus on stubble tillage methods, glyphosate application and the application of the pre-emergence herbicide cinmethylin in two rates. Control efficiencies of 99-100% were achieved by ploughing, double glyphosate application or via false seedbed preparation, each in combination with a cinmethylin application. In the last article, over a period of three years the new pre-emergence herbicide cinmethylin was tested in combination with stubble treatments and delayed drilling of winter annual cereals in winter wheat and winter triticale in Southwestern Germany. Cinmethylin controlled 58-99% of A. myosuroides plants until 120 days after sowing. Additive and synergistic effects of cinmethylin and delayed drilling were found for all studies. In this study, the focus was set on monitoring, cultural and direct weed control methods. Considering especially A. myosuroides, a diverse control strategy needs to be implemented to ensure a sustainable and reduced herbicide use, high control levels, minimized crop damage, safeguarded grain yields and reduced risk of resistance development. However, IWM measures imply increased system complexity, which may make their adoption by farmers difficult. Nevertheless, the results show that cinmethylin can be successfully used for weed control systems in combination with different stubble tillage methods, glyphosate application, delayed seeding, or herbicide sequences and mixtures, making it a valuable tool in integrated weed and resistance management strategies with its novel and unique mode of action.
Integrated management, analysis of mechanisms and early detection of resistant populations of Alopecurus myosuroides HUDS. and Apera spica-venti L. Beauv.
(2015) Kaiser, Yasmin; Gerhards, Roland
The control of pests is one of the major challenges in agricultural production worldwide. Especially weeds cause severe yield losses by competing with crops for light, space, water and nutrients. Due to the relatively low costs for acquisition and application of herbicides and a high control efficacy, chemical measures are predominantly applied to control weeds. In Europe, Alopecurus myosuroides HUDS. (blackgrass) and Apera spica-venti L. Beauv. (silky windgrass) are major weeds especially in winter wheat. The occurrence at high population densities in combination with a consequent use of herbicides with the same modes of action has resulted in the selection of resistant populations. Populations with target-site resistance (TSR) as well as non-target-site resistance (NTSR) could be confirmed for A. myosuroides and A. spica-venti. In contrast to the mechanisms of TSR, NTSR mechanisms are less investigated. Due to the steadily increasing number of putative herbicide resistant weed populations, the demand for rapid resistance tests is rising. The papers of the dissertation focus on the integrated management, the investigation of resistance mechanisms and the detection of herbicide resistant weed populations. The following research objectives have been examined within the four work packages (papers): – To develop a new methodology for a rapid detection of herbicide resistance and to confirm that results are comparable with classical greenhouse approaches – To investigate metabolism of herbicides in sensitive and resistant populations of A. myosuroides to gain comprehensive knowledge on resistance mechanisms – To evaluate the influence of agronomic factors on the probability of resistance occurrence and to develop a geo-referenced database for mapping the spread of herbicide-resistant A. spica-venti populations across Europe – To assess the influence of crop rotation and herbicide strategies on population development and herbicide resistance of A. myosuroides and crop yield The four papers come to the following results regarding the main research objectives: 1st paper: A laboratory test was developed to accelerate the detection of herbicide resistance. Therefore, A. myosuroides was cultivated in wellplates containing nutrient agar and herbicides. The evaluation of herbicide resistance was conducted by a sensor, measuring chlorophyll fluorescence. The results of the developed test corresponded well to the standard whole-plant pot tests in the greenhouse. In both tests sensitive and resistant populations were identified, however results of the Chlorophyll Fluorescence Imaging were available earlier. 2nd paper: Metabolism of herbicides was investigated in populations of A. myosuroides by using liquid chromatography - tandem mass spectrometry (LC-MS/MS) to gain comprehensive knowledge on mechanisms of herbicide resistance. NTSR populations differed from sensitive and TSR A. myosuroides in form of an enhanced degradation of the active ingredient or metabolite, depending on the investigated herbicide. For the investigated herbicides (inhibition of ACCase and ALS) it was shown that herbicide metabolism plays an important role regarding herbicide resistance in A. myosuroides. 3rd paper: To evaluate the influence of agronomic factors on the probability of resistance occurrence in A. spica-venti, numerous populations were screened in the greenhouse. The corresponding field history obtained from questionnaires and the results of greenhouse assays were used to develop a GIS-database in which herbicide-resistant A. spica-venti populations were mapped. The statistical analysis revealed that a high percentage of winter crops in the crop rotation, together with conservation tillage, early sowing dates and high population density increased the occurrence of herbicide resistance in A. spica-venti. 4th paper: To assess the impact of crop rotation and herbicide strategies on A. myosuroides, field studies at two locations in Southern Germany have been carried out. Results show that densities of A. myosuroides increased in continuous winter wheat. The introduction of spring crops significantly reduced densities, even without using herbicides. Furthermore it has been shown that the risk of herbicide resistance was reduced when performing a consequent change of herbicide mode of action. The use of herbicides with only one mode of action increased the number of herbicide resistant plants. Crop yield was notably influenced by A. myosuroides in winter wheat. The overall results of this dissertation showed the great impact of agricultural measures on herbicide resistance in A. myosuroides and A. spica-venti and demonstrated opportunities for prevention and management. The developed resistance quick test provides an accelerated detection of herbicide resistance and therefore the chance to initiate resistance management strategies much earlier.