Incorporating agronomic measures into integrated weed management strategies using pre-emergence herbicide cinmethylin to control Alopecurus myosuroides Huds.

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.Alopecurus myosuroides Huds. ist eines der problematischsten Grasunkräuter im Getreideanbau in Westeuropa. Der verstärkte Anbau von einjährigen Winterkulturen, der wiederholte Einsatz von Herbiziden mit gleichen Wirkmechanismen, reduzierte Bodenbearbeitung und frühe Aussaattermine von Getreide führen zu steigenden Populationsdichten von A. myosuroides. In der landwirtschaftlichen Praxis wird häufig aufgrund ihrer hohen Flexibilität, Bekämpfungserfolge sowie den geringen Kosten auf Herbiziden zur erfolgreichen Bekämpfung von A. myosuroides zurückgegriffen. Durch die Zunahme an Herbizidresistenten Unkrautpopulationen, sowie durch europäische und nationale Beschränkungen sind die Landwirte gezwungen, den Herbizideinsatz zu reduzieren, um die negativen Auswirkungen auf die Umwelt und die Rückstände in Nahrungskette zu minimieren. Als ganzheitlicher Ansatz zur Reduzierung des Herbizideinsatzes und die damit verbundenen negativ Auswirkungen, stellt das integrierte Unkrautmanagement (IWM) eine Diversifizierung der Bekämpfungsstrategie von A. myosuroides dar. Um eine integrierte Bekämpfungsstrategie von A. myosuroides in Wintergetreide zu entwickeln, wurden im Rahmen dieser Arbeit verschiedene Aspekte von IWM einzeln untersucht bzw. kombiniert. Besondere Aufmerksamkeit wurde hierbei dem neuen Wirkstoff Cinmethylin geschenkt, welches durch seinen neuen Wirkungsmechanismus eine Erweiterung des Vorauflaufherbizidrepertoires in Wintergetreide zur Bekämpfung von A. myosuroides darstellt. Der erste Artikel befasst sich mit der Entwicklung eines Agar Biotests zur Bestimmung von Sensitivitätsunterschieden in A. myosuroides Populationen gegenüber den in Vorauflaufherbiziden enthaltenen Wirkstoffen Flufenacet und Cinmethylin. Alle getesteten Populationen zeigten keine reduzierte Sensitivität gegenüber Cinmethylin, dennoch wurden Unterschiede in den Resistenzfaktoren zwischen dem Agar Biotest und dem Standard Gewächshaus Biotest festgestellt. Die Ergebnisse des Gewächshaus Biotests konnten zum größten Teil für Cinmethylin und Flufenacet durch den Agar Biotest reproduziert werden und damit ein effizienteres Testsystem geschaffen werden. Der zweite Artikel konzentrierte sich auf vorbeugende Unkrautbekämpfungsmaßnahmen wie Zwischenfruchtmischungen, verschiedene Stoppelbearbeitungsmethoden und Glyphosatbehandlungen und deren Auswirkung auf die Unkrautbekämpfung, insbesondere auf A. myosuroides und Ausfallweizen. Die Ergebnisse zeigen, dass neben einer doppelten Glyphosatanwendung auch gut etablierte Zwischenfruchtbestände das Potential für einen hohen Unkrautbekämpfungserfolg von A. myosuroides bieten. Der dritte Artikel befasste sich mit der Kombination vorbeugender Unkrautbekämpfungsmaßnahmen (Früher-, Später-Saattermin) sowie dem Einsatz unterschiedlicher Herbizide. Die Ergebnisse zeigen, dass vorbeugende Bekämpfungsmaßnahmen wie die Spätsaat, die Bestandsdichte von A. myosuroides um bis zu 75% reduzieren konnte. Dennoch sollten zum Erreichen eines Bekämpfungserfolges von > 95% zusätzliche zur Wahl des Saattermines, Herbizide eingesetzt werden. Im vierten Artikel wurde über eine Periode von zwei Jahren auf zwei Standorten vier Feldversuche angelegt, bei dem die Kombination aus Stoppelbearbeitung, einer Glyphosatanwendung sowie die Anwendung des in Vorauflaufherbizid enthaltenen Wirkstoffs Cinmethylin in zwei Aufwandmengen im Vordergrund standen. Durch die Kombinationen von Cinmethylin mit pflügen, doppelter Glyphosatanwendung oder durch die Kombination mit einer falschen Saatbettbereitung konnten Bekämpfungserfolge von A. myosuroides von 99-100% erzielt werden. Im letzten Artikel wurde über einen Zeitraum von drei Jahren das neue Vorauflaufherbizid Cinmethylin in Kombination mit verschiedenen Stoppelbearbeitungsstrategien und einer verzögerten Aussaat von Wintergetreide in vier Feldversuchen mit Winterweizen und Wintertriticale im Südwesten Deutschlands getestet. Cinmethylin kontrollierte 120 Tage nach der Aussaat, 58-99 % der A. myosuroides-Pflanzen. Additive und synergistische Effekte von Cinmethylin und verzögerter Aussaat wurden in allen Studien festgestellt. In dieser Studie lag der Fokus auf dem Monitoring, vorbeugenden sowie chemischen Unkrautbekämpfungsmethoden. Konkret bedeutet dies, dass durch vorbeugende Bekämpfungsmaßnahmen vor der Aussaat der Hauptkultur ungünstige Wachstumsbedingungen für Unkräuter geschaffen wurden. IWM-Maßnahmen implizieren jedoch eine erhöhte Systemkomplexität, was ihre Akzeptanz durch die Landwirte erschweren kann. Die Ergebnisse dieser Studie zeigen, dass Cinmethylin in Kombination mit verschiedenen Stoppelbearbeitungsmethoden, Glyphosatanwendungen, Spätsaat oder Herbizid Sequenzen/-mischungen zu nachhaltigen Bekämpfungserfolg führt. Cinmethlyin stellt mit seiner neuartigen und einzigartigen Wirkungsweise eine wertvolle Ergänzung für ein integriertes Unkraut- und Resistenzmanagement dar

Weed Suppressive Ability of Cover Crop Mixtures Compared to Repeated Stubble Tillage and Glyphosate Treatments

The utilization of an effective stubble management practice can reduce weed infestation before and in the following main crop. Different strategies can be used, incorporating mechanical, biological, and chemical measures. This study aims at estimating the effects of cover crop (CC) mixtures, various stubble tillage methods, and glyphosate treatments on black-grass, volunteer wheat and total weed infestation. Two experimental trials were conducted in Southwestern Germany including seven weed management treatments: flat soil tillage, deep soil tillage, ploughing, single glyphosate application, dual glyphosate application, and a CC mixture sown in a mulch-till and no-till system. An untreated control treatment without any processing was also included. Weed species were identified and counted once per month from October until December. The CC mixtures achieved a black-grass control efficacy of up to 100%, whereas stubble tillage and the single glyphosate treatment did not reduce the black-grass population, on the contrary it induced an increase of black-grass plants. The dual glyphosate application showed, similar to the CC treatments, best results for total weed and volunteer wheat reduction. The results demonstrated, that well developed CCs have a great ability for weed control and highlight that soil conservation systems do not have to rely on chemical weed control practices

Development of an Agar Bioassay Sensitivity Test in Alopecurus myosuroides for the Pre-Emergence Herbicides Cinmethylin and Flufenacet

Rapid and reliable tests for pre-emergence herbicide susceptibility in weeds are important to test a wider range of accessions on their baseline sensitivity, as well as to provide information on putative resistance. This study focused on the development of an agar quick test to determine sensitivity differences in Alopecurus myosuroides Huds. to pre-emergence herbicides containing flufenacet and cinmethylin. The new agar quick test and a standardized whole plant pot bioassay were conducted twice in 2019. For both test systems, seeds of 18 populations of A. myosuroides originated from Southwest Germany and Great Britain were used and treated with discriminating rates of herbicides in dose-response studies. After 28 days, the above-ground dry matter of the plants was determined and the resistance factors were calculated. The agar test was able to provide information on the resistance status of the tested biotype within 12 days. All populations did not show reduced sensitivity to cinmethylin. Within three populations, differences in sensitivity levels were observed between the two test systems. As cinmethylin is not yet marketed in Europe, these resistance factors can also be considered as a baseline sensitivity for A. myosuroides. For flufenacet, the resistance factors differed significantly from the whole plant pot bioassay and the agar test for the biotypes A (0.35, 13.1), C (0.56, 13.2), D (1.87, 12.4), E (15.5, 3.5) and H (2.95, 14). It was possible for the most part for the cinmethylin tested populations to confirm the results of the standardized whole plant pot bioassay in the agar bioassay sensitivity tests, and hence create a promising, faster test system

Yield, soil Nitrogen content and weed control in six years of conservation agriculture on-farm field trials in Southwest Germany

Conservation Agriculture (CA) is a farming system that aims to protect soil resources by promoting minimum soil disturbance in combination with the maintenance of a permanent soil cover, and diversification of crop rotation. The aim of this study was to investigate the effects of no-till and shallow conservation tillage using a chisel plough and rotor tiller on loamy soils with high clay contents in combination with cover crop mixtures in rotations with at least three different crops. Crop yield, soil Nitrogen content and weed coverage were the main parameters measured. Experiments were performed in an on-farm approach in southwest Germany on 18 farms and two research stations over a period of 6 years. Yields of cereals, oilseed rape, maize, soybean and peas were slightly lower under no-tillage with 5.8–7.3 Mg grain yield equivalents ha− 1 than under conservation tillage with 6.3–7.8 Mg grain yield equivalents ha− 1. Cover cropping did not affect crop yields. Tillage and cover cropping had no influence on weed control in the subsequent main crop. Soil nitrate contents before winter in November were on average 11 kg N ha − 1 lower in the cover crop treatments compared to the plots without cover crops.This study shows that CA with minimum tillage had slight advantages compared to the no-till system under Southwest Germany farming condition

Crop Response to Leaf and Seed Applications of the Biostimulant ComCat® under Stress Conditions

Although clear evidence for benefits in crop production is partly missing, several natural compounds and microorganisms have been introduced to the market as biostimulants. They are supposed to enhance nutrient efficiency and availability in the rhizosphere, reduce abiotic stress, and improve crop quality parameters. Biostimulants often derive from natural compounds, such as microorganisms, algae, and plant extracts. In this study, the commercial plant extract-based biostimulant ComCat® was tested in two field experiments with maize in the communities of Banikoara and Matéri in Northern Benin and six pot experiments (four with maize and two with winter barley) at the University of Hohenheim in Germany. Maize was grown under nutrient deficiency, drought, and weed competition, and winter barley was stressed by the herbicide Luximo (cinmethylin). ComCat® was applied at half, full, and double the recommended field rate (50, 100, and 200 g ha−1) on the stressed and unstressed control plants as leaf or seed treatment. The experiments were conducted in randomized complete block designs with four replications. The above-ground biomass and yield data of one experiment in Benin were collected. The biostimulant did not promote maize and winter barley biomass production of the unstressed plants. When exposed to stress, ComCat® resulted only in one out of eight experiments in higher barley biomass compared to the stressed treatment without ComCat® application. There was a reduced phytotoxic effect of cinmethylin after seed treatment with ComCat®. Crop response to ComCat® was independent of the application rate. Basic and applied studies are needed to investigate the response of crops to biostimulants and their mechanisms of action in the plants before they should be used in practical farming