Browsing by Subject "Unkraut"

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An image analysis and classification system for automatic weed species identification in different crops for precision weed management
(2010) Weis, Martin; Gerhards, Roland
A system for the automatic weed detection in arable fields was developed in this thesis. With the resulting maps, weeds in fields can be controlled on a sub-field level, according to their abundance. The system contributes to the emerging field of Precision Farming technologies. Precision Farming technologies have been developed during the last two decades to refine the agricultural management practise. The goal of Precision Farming is to vary treatments within fields, according to the local situation. These techniques lead to an optimisation of the management practice, thereby saving resources, increasing the farmers outcome, reducing the overall management costs and the environmental impact. A successful introduction of Precision Farming involves the development of application equipment capable of varying treatments and sensor technology to measure the spatial heterogeneity of important growth factors. Such systems are able to record, store and use large amounts of data gathered by the sensors. Decision components are needed to transform the measurements into practical management decisions. Since the treatments are varied spatially, positional data, usually measured using GPS technology, has to be processed. The located measurements lead to a delineation of management zones within a field and are represented by geo-data and can be visualised in maps. The improved, detailed knowledge of the situation within the field leads to new and extended scopes of applications and allows to document the management practices more precisely. In this work, parts of Precision Farming technology were developed for site-specific weed management. Five selected publications are presented, covering the technological prerequisites and details of the developed system.
Cover cropping in integrated weed management
(2018) Sturm, Dominic; Gerhards, Roland
Weed control constitutes a major challenge in the worldwide crop production. Beside chemical and mechanical weed control strategies, cover cropping provides an effective way of biological weed suppression. Five different field experiments were conducted at six locations from 2014-2016 to evaluate the weed control efficacy of different cover crops in mono and mixed cultivation combined with different fertilization strategies and sowing dates. Furthermore weed suppressing effects of cover crop mulches in spring and of living mulches in summer were investigated. Potential effects on sugar beet emergence, quality and quantity were also assessed. In three laboratory and two greenhouse experiments from 2015-2017, the proportional contribution of competitive and biochemical effects on the overall weed suppression and the identification of varying susceptibilities of different weeds against biochemical stresses were at the center of research. In field experiments, the weed suppressive effects of cover crops and living mulches in mono and mixed cultivation were tested. The experiments emphasized the importance of cover crop and living mulch mixtures compared to mono cropping due to a higher flexibility to biotic and abiotic stresses. This was followed by a more constant biomass production and more effective weed suppression. Moreover, the observed weed control was a result of competitive and biochemical effects, induced by cover crops. These were later on analyzed for active weed growth suppressing compounds. Altering cover crop sowing date and fertilization to optimize the weed control resulted in significant changes of cover crop and weed biomass. Early cover crop sowing five or three weeks before winter wheat harvest increased the weed control efficacy in one year, significantly. Due to contrary results over the two experimental years, we suggest that the cover crop biomass and consequently the weed suppressive ability depends on sufficient soil water for rapid cover crop germination and growth. The use of cover crop mulch in sugar beet crops provided a weed suppression of up to 83%. Especially mulch derived from cover crop mixtures reduced the weed density (56%) more effectively compared to mono cultivated cover crops (31%). The inclusion of cover crops, mulches and living mulches can lead to significant herbicide reductions in the main crop. However supplementary mechanical or chemical weed control strategies are still necessary, especially in crops with a low competitive ability like sugar beets. Nevertheless, novel mechanical weed control approaches and adequate herbicide application techniques, as band-spraying, can reduce the herbicide input in the long-term. Germination tests with aqueous cover crop extracts were conducted on weed seeds to evaluate differences in the inhibition of germination and root growth. Furthermore, different sensitivities of the weeds against the different cover crop extracts were revealed. Some cover crops as S. alba, F. esculentum, H. annuus, T. subterraneum and L. usitatissimum showed the most effective weed suppression. Moreover, the weed M. chamomilla showed the highest susceptibility against biochemical stresses in the germination tests. A strong positive correlation between the weed suppressive effects by the extracts and the field weed suppression was found. This indicated that biochemical effects play also an important role on the overall weed suppression in the field. To estimate the proportions of competitive and biochemical effects on the overall weed suppression by cover crops, greenhouse experiments with active carbon supplemented soil were conducted. These experiments revealed that biochemical effects, by the presence of active carbon in the soil, shifted the balance of competition between cover crops and weeds. In the course of the experiments, we also found species-specific effects on the donor as well as on the receiver side. The results of this thesis demonstrate the diverse use of cover crops, their mulches and living mulches in agricultural systems. This work aims on the optimization of biological weed control strategies and indicates approaches for future research. It is for example not yet clear how cover crops suppress specific weeds and if it is possible to design combinations of specific cover crops for the suppression of individual weed communities. Additionally, these results help to reduce long-term herbicide inputs in agricultural systems.
Evaluating different management strategies to increase the effectiveness of winter cover crops as an integrated weed management measure
(2020) Schappert, Alexandra; Gerhards, Roland
Weed control in agricultural production systems is indispensable to achieve stable crop yields. Integrated cropping systems are demanding for preventive and ecologically harmless weed control measures in order to protect soil and water resources and to retard the selection of herbicide-resistant weeds. Well-established winter cover crops provide nutrient retention and soil protection and may effectively suppress weeds. This contributes to reduce chemical and mechanical fall- and spring-applied weed control practices. However, producers are cautious towards integrating cover crops in crop rotations, as their performance is related to environmental conditions and varies, therefore, significantly from season to season. To increase their integration into cropping systems, reliability on weed control by cover crops needs to improve. In the current study, management strategies such as i) the cover crop sowing method, ii) the selection of water deficit tolerating cover crop species, iii) cover crop species combinations, iv) the adjustment of the mulching date and v) tillage practices after cover crop cultivation were considered as possibilities to improve the effectiveness of cover crops to control weeds during cultivation and in the subsequent cash crop. Within the first and the second publication, the general weed and A. myosuroides control ability of a cover crops mixture during and after cultivation were compared in the field with various fall-applied tillage methods and glyphosate treatments. Due to the development of highly competitive cover crop stands, weeds were suppressed by 98% and A. myosuroides by 100% during cultivation. Therefore, cover crops were more efficient compared to glyphosate application(s), non-inversion and inversion tillage and revealed a great potential to reduce or even replace chemical and mechanical fall-applied weed control measures. The efficient A. myosuroides control during the cover crop cultivation remained until spring barley harvest. This quantifies cover crops to complement herbicide resistance management strategies. In contrast, due to the weak cover crop performance during fall-to-winter within another two experiments included in the second article, weed suppressive effects of cover crops disappeared after the cultivation of cover crops. This might have been the reason why reduced tillage and adjusted mulching dates in spring failed in contributing to expand weed suppressive effects of cover crops in these experiments. Cover crop mixtures are attributed to show a greater resilience against unfavorable conditions than pure cover crop stands which is expected to result in an increased weed suppression ability. Within article three, the weed control efficacy of pure cover crop stands was compared with species mixtures. Pure stands of Avena strigosa Schreb. and Raphanus sativus var. oleiformis Pers. provided the most efficient weed control with 83% and 72%, respectively. Cover crop species mixtures showed a weaker weed suppression ability than the most efficient pure stand. In order to improve the weed control ability of cover crop mixtures, it was evaluated that the species selection is more relevant than the species diversity. Thereby, environmental requirements, such as water and temperature demand, and weed suppression mechanisms should be considered. Weed suppression of mixtures was improved by increasing the proportions of A. strigosa and R. sativus var. oleiformis, as they were showing a susceptibility for dry conditions and combine a strong competition for resources and allelopathic interference with weeds. Within the fourth article, it was explored whether a low susceptibility of single cover crop species to water-limitations accompanies an improved weed suppression ability. A. strigosa and Sinapis alba L. showed differing suitabilities to cope with water-deficit in the greenhouse. A relation between weed suppression and water demand of cover crops at the field was not identified. Although the weed control ability of cover crops is generally narrowed under water-limited conditions, the weed suppression potential of individual species seems to be independent of their water supply. The adjustment of the cover crop sowing method, the consideration of species-specific requirements and the mixing strategies, were evaluated as being important to improve the resilience of cover crops against severe environmental conditions and their weed control ability. Investigations of cover crop mixtures with respect to single component species, their mixing ratios and seed densities, might further increase the absolute and average effectiveness of cover crops as an integrated weed management practice.
Generative sowie vegetative Vermehrung, Entwicklung, Morphologie und chemische Bekämpfung der windenden Unkrautarten: Calystegia sepium (L.) R. Br., Convolvulus arvensis L., Ipomoea hederacea Jacq., Ipomoea purpurea (L.) Roth und Fallopia convolvulus L.
(2013) Willeke, Leonie; Gerhards, Roland
Vining weed species as the two perennial plants Calystegia sepium and Convolvulus arvensis, and the annual species Ipomoea hederacea, Ipomoea purpurea and Fallopia convolvulus are very important in agriculture worldwide due to their high competitive ability. The aim of this work is to gain a better understanding of the morphology, physiology and reproduction of these species and the efficacy of herbicides on the weeds to develop improved control strategies with this knowledge. The first section of this paper consists of studies about the generative propagation and seed germination in response to various factors. It is shown that the species of the family of Convolvulaceae have morphological similarities and any weed species can germinate in a wide temperature range and in all studied soil types. The proliferation studies revealed that the rhizome and root pieces of Calystegia sepium and Convolvulus arvensis are dormant in the winter and sprout in spring. In addition, several buds on rhizome and root pieces also directly next to each other can sprout and the percentage of sprouting increases with the number of buds. Additionally, a negative linear relationship between the burial depth of the rhizome and root pieces in the soil and the ability to emerge is determined. In addition to these results, the analysis of the starch and sugar concentrations during a growth period shows that the starch concentration reaches its minimum 1.5 months before flowering. In the second part of this work, the main focus is placed on weed control with herbicides especially with the novel active substance TCM (Thiencarbazone-methyl), an acetolactate synthase (ALS) inhibitor, whose mechanism is investigated. The active ingredient TCM remains stable in the vining weeds and does not degrade as in corn. Proven TCM is absorbed through the leaves and transported systemically. TCM causes a disruption of the amino acid balance. The increase of the branched amino acids is carried out in dependence of the time as well as the applied herbicide concentration. TCM under greenhouse conditions as well as the active ingredients dicamba, glufosinate and glyphosate, frequently used in corn, control annual and perennial weed species germinated from seeds to a degree of more than 85% in the full and half field application rate. In comparison, the efficacy of shoot control of vegetatively propagated perennial plants is about 5-15% lower. Nevertheless, the regrowth of rhizome and root pieces is suppressed by the herbicide applications almost completely. The studies of the control in different growth stages show that the effect of TCM, dicamba and glyphosate on the annual species is greater in earlier stages of growth; however, the generatively propagated plants are controlled constantly even high in the later stages of growth. In contrast, with an increasing shoot length from 5 cm to 30 cm, the efficacy of control of the vegetatively propagated plants decreases to an average 40 %. The obtained control of Calystegia sepium and Convolvulus arvensis after a spring and a fall application under field conditions is much lower than under greenhouse conditions. Post-emergence application at recommended field application rates results in a reduction in the aboveground biomass of Calystegia sepium with TCM about 65% and of Convolvulus arvensis to a maximum of 50% with TCM, TCM in combination with TBT(tembotrione) and dicamba. The herbicides dont reduce the sprouting ability of underground organs of both species; and corn yield isnt even increased by the use of a herbicide against Convolvulus arvensis. Fallopia convolvulus, an annual species, is controlled in field trials by TCM and TCM in combination with TBT in the normal field application rate to an extent of more than 90 %, also with dicamba. The control results of Ipomoea hederacea in the two experimental years vary greatly. On average, the efficacy of the application of TCM in combination with IFT (isoxaflutole), glufosinate and dicamba in combination with diflufenzopyr is as high as in the greenhouse experiments with a rate of 95 %. In summary, the results show that young plants germinated from seeds in early growth stages can be controlled quite well above and below ground with the studied herbicides, so that TCM can be used to control Fallopia convolvulus as an alternative to other herbicides used conventionally. Despite the proven systemic translocation and inhibition of regrowth of rhizome and root pieces of vegetatively propagated perennial species TCM as well as the other tested herbicides do not provide suffcient long-term success of control of Calystegia sepium and Convolvulus arvensis in spring and in fall application under field conditions. The mechanical control of perennial species can be optimized by a strong division of the rhizome and root pieces in combination with a high burial depth.
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.
Integrated weed control in sugar beet (Beta vulgaris), using precision farming technologies and cover cropping
(2017) Kunz, Christoph; Gerhards, Roland
Weed control is one of the major challenges in sugar beet (Beta vulgaris) production worldwide. Due to the high flexibility and low costs, herbicide applications are the common agricultural practice for successful weed control. Yet, due to European and national restrictions, farmers are forced to substitute their herbicide input in order to reduce the chemical influence on the environment. Beside chemical weed control systems, integrated weed management (IWM), can be an alternative, to reduce the chemical preponderance. The five essential parts in composing a successful IWM system are: i) cover crops (CC) and ii) resulting mulch residues which can decrease the weed infestation prior to the actual crop establishment, iii) living mulches which can suppress weeds during the crop growth period and iv) precision mechanical weed control which can provide herbicide reductions. Last but not least v) herbicide applications should be optimized with sensor technologies to identify and reduce stress on crops. In the current study, all the named aspects of IWM were examined in sugar beets. In order to accomplish that, the following research objectives were investigated and answered in the course of the papers composing this thesis: • Evaluation of the suitability of CC and CC mixtures for weed suppression prior to sugar beet sowing • Assessment of differences in sugar beet emergence, weed control and biomass under different CC mulches • Application of living mulches and measurement of their weed control efficacy during the sugar beet growth period • Evaluation of mechanical weed control along with chemical band spraying compared to an overall herbicide application • Determination of the weed control efficacy of mechanical weeding by using visual sensors and GNSS-RTK • Investigation of the feasibility of intra-row mechanical weed control, its prerequisites and limitations • Detection of responses to herbicides by using chlorophyll fluorescence imaging technology 1st paper: Field and laboratory experiments were conducted to investigate the competitive and biochemical weed suppressive ability of CC. Applied aqueous CC extracts in germination tests inhibited weed growth and potential allelochemicals were identified. In the field all CC either in mixture- or mono-cultivation were able to suppress weeds compared to an untreated control by 66%. In the 2nd and 3rd paper sugar beet plant emergence was investigated in greenhouse and field experiments, in order to evaluate the influence of various CC mulches on weed suppression. Different CC mulches reduced weed germination successfully. During one dry growing season sugar beet emergence was enhanced by increased soil moisture due to the existence of a CC mulch layer compared to uncovered soil. Our findings suggest that CC mulch layers can substantially effect crop and weed development within the field. To assess the weed suppressive ability of living mulches in sugar beets, field studies were carried out at four sites in southern Germany, presented in the 4th paper. Results show that living mulches can reduce the total amount of different weed species in the inter-row area up to 71%. The white sugar yield was increased in average by 42% with the existence of living mulch as compared to the untreated control. In the 5th, 6th and 7th paper sensor technologies were used for mechanical weed control combined with chemical band application to reduce the herbicide input, with similar weed control results to the overall chemical application. Sensor based, mechanical precision steering technologies, reduced weeds more effectively than when compared to manual operator guidance. This is due to accurate fast driving speeds close to the crop area. Intra row elements (finger weeder, rotary harrow, torsion weeder, heap element) for mechanical weed control showed effective weed suppression. Nevertheless, suitable soil and weather conditions for mechanical weed control were not always given, which can result in an efficacy loss. Finally, in the 8th paper, a portable sensor, based on chlorophyll fluorescence imaging, was used in greenhouse experiments to investigate the response of plants after herbicide application. Various active ingredients have shown different damage concerning the photosystem II. The use of this sensor can quantify phytotoxic effects due to herbicides and can help to find the most suitable herbicide application date, active ingredients or herbicide mixture. The overall result of this dissertation reveals the great potential of CC, living mulches, precision mechanical methods and sensor technologies as part of an IWM system in sugar beet production.
Integrated weed management in a pesticide free area
(2023) Saile, Marcus; Gerhards, Roland
Weed control is a challenging task for farmers in highly specialized crop production systems. The competition of weeds for light, nutrients and water causes significant yield losses. Chemical weed control is still the standard method in European cropping systems. Due to their high selectivity and efficacy against a wide range of weed species, herbicides provide the most efficient weed control in most crops. However, negative impact of herbicides on the environment, loss of biodiversity, possible risks to consumers due to residues in food chain and the increase and spread of herbicide-resistant species force farmers to reduce herbicide use and call for alternative weed control methods. Mechanical weed control methods including hoeing and harrowing represent the most promising alternative direct weed control methods. Weed control costs for mechanical methods are still higher than for herbicides and weed control efficacy is often lower with less than 80 % compared to around 95 % for herbicides. The efficacy of mechanical weed control is dependent on external factors such as soil water content, soil texture, and weed species diversity in the particular field. Herbicides can therefore not be replaced by a single mechanical weed control method. It needs an Integrated Weed Management (IWM) strategy including preventive and direct methods of weed suppression. In this study, IWM were investigated for typical arable farming systems in Southwestern Germany. Studies for this thesis were conducted from 2017 to 2022. The objectives of the thesis were to combine preventive and curative methods of weed control in diverse cropping systems and to improve mechanical weed control methods by precision farming technologies. The results of the thesis have been published in five papers. The first article addressed the effects of preventive weed control by stubble tillage, cover cropping, and the use of glyphosate treatments against Alopecurus myosuroides and volunteer cereals. In two field trials at two sites, cover crop mixtures achieved equal weed control efficacy of up to 100 % as the dual glyphosate treatment. Stubble tillage practices resulted in lower control but caused the highest energy consumption. The second article focused on the effect of two seeding dates (early-, delayed-sowing) and different herbicide strategies on A. myosuroides control on winter cereals. This study was conducted over three years at three locations. Delayed sowing reduced weed emergence by 30-40 %. Delayed sowing in combination with the pre-emergence herbicide cinmethylin provided equal weed control efficacy as a combination of pre-emergence and post-emergence herbicides. The third article focused on the control of A. myosuroides including the combination of integrated stubble management and various application rates of the pre-emergence herbicide cinmethylin. In four field trials over a two-year period, the pre-emergence herbicide cinmethylin was applied at two application rates at two sites. Control success of up to 100 % was achieved through the combination of inversion tillage, false-seedbed preparation and the reduced rate of cinmethylin. The results also showed a high variation of the effect of preventive measures. The fourth article deals with IWM in spring oats and winter wheat. Field experiments were conducted at two locations over two years in five field trials. Chemical weed control was combined with sensor-based mechanical weed control. Data showed that sensor-based mechanical weed control (hoeing and harrowing) in the field trials achieved equal weed control efficacy of up to 100 %. However, highest grain yields were recorded for the combination of pre-emergence herbicide and post-emergence mechanical weed control. The last article dealt with a new cultivation system without chemical synthetic pesticides but with mineral fertilizers (MECS). The hypothesis was that MECS would increase the competitiveness of the crop on the weeds and generate higher yield benefit compared to the organic cultivation system. Field trials were conducted at four sites over two years. Three different cropping systems, an organic cropping system managed according to organic farming guidelines, a conventional cropping system and a MECS, were compared in a 5-year crop rotation. After two years of studies, no clear conclusion can be made how MECS affects the interaction of crops and weeds. Weed control efficacy in MECS was lower than organic farming. The increase in weed pressure in MECS will cause problems in the subsequent crops. Yields were significantly higher in MECS compared to the organic system and only slightly lower than in the conventional system. It can be concluded from these studies that IWM in combinations with precision farming technologies for mechanical weeding can replace herbicides. However, weed control costs were higher with non-chemical weed control methods.
Interactions of farming and plant biodiversity in weed control related ecosystem service provision and weed conservation
(2020) Schumacher, Matthias; Gerhards, Roland
There is evidence that diverse plant communities in terrestrial ecosystems are either more stable or more productive in terms of food web support and ecosystem service provision. In agro-ecosystems, characterized by high disturbance and external inputs, plant diversity and their services can only be provided by weeds. In the first study, vegetation recordings and farmer surveys were conducted in on-farm experiments in two regions of Southwestern Germany. The aim was to examine the effects of agricultural management on weed community composition, weed biodiversity and occurrence of rare arable weed species in cereal fields. Weed biodiversity was influenced mainly by crop species, herbicide use and farming system as well as nitrogen and light availability. Weed communities were quite similar in both study regions and dominated by Alopecurus myosuroides, Galium aparine, Viola arvensis, Polygonum convolvulus and Veronica persica. A redundancy analysis revealed that the weed community was mainly shaped by crop species, tillage, location in the field and timing of herbicide application. The results highlight the erosion of weed communities due to intensive agricultural practices and emphasize the conservation of weed biodiversity per se and rare arable weed species in particular. The next aim was to examine if this biodiversity is able to support weed control related ecosystem services, like the predation of weed seeds. The objectives of this study were to investigate the connection between weed biodiversity, Carabid beetle diversity and weed seed predation as well to evaluate the role of farming intensity in this sequence. For this purpose, on-farm experiments were performed on the Eastern Swabian Alb. A positive correlation between weed biodiversity and Carabid beetle diversity was identified as well as a pattern of medium Carabid beetle diversity providing the highest weed seed predation. There was no consistent influence of farming intensity on weed seed predation. The revealed connection between weed diversity, Carabid beetle diversity and weed seed predation highlights the role of plants in food web support and subsequent ecosystem service provision. The utilization of these services depends on the promotion of biodiversity by designing appropriate management strategies. In the next step, the general principles underlying ecosystem service provision by biodiversity, were conveyed to a cover cropping system. The aim was to test single sown cover crops and species mixtures in terms of weed suppression efficacy and reliability. For this purpose, cover crop species were sown singly and as mixtures in a field experiment. Lower weed dry matter and weed densities were found predominantly in treatments with favorable establishment and above-average biomass production. Mixtures performed much more homogeneous in regard to the measured parameters compared to single sown cover crops. The results suggest that, although particular single sown cover crops are more effective to control weeds than mixtures, mixtures are more reliable under changing conditions. Altering the species composition of cover crop mixtures according to more complementary traits might further improve their weed control efficacy. The results of this dissertation demonstrate the importance of plant biodiversity in the provision and reliability of weed control related ecosystem services, either by weeds themselves or by specifically designed cover crop mixtures. Furthermore, management factors influencing weed biodiversity were determined, which can aid in the creation of more sustainable management strategies for a diverse agroecosystem and the conservation of rare arable weed species.
The biocontrol agent Fusarium oxysporum f. sp. strigae - Monitoring its environmental fate and impact on indigenous fungal communities in the rhizosphere of maize
(2016) Zimmermann, Judith; Cadisch, Georg
The fungal biocontrol agent (BCA) Fusarium oxysporum f. sp. strigae (Fos) has proven to be effective in the suppression of the parasitic weed Striga hermonthica, which causes substantial yield losses in cereals in Sub-Saharan Africa. A prerequisite for widespread implementation of the biocontrol technology is the official registration of the BCA Fos by country authorities in Sub-Saharan Africa. The FAO and OECD institutions established international registration regulations to ensure the environmental safety of microbial BCAs. The present thesis aimed on assessing the potential of the BCA Fos to meet these registration requirements and was, therefore, based on the following two major objectives: (1) A specific DNA-based monitoring tool for Fos was developed which allows following its population kinetics in soils as driven by contrasting environmental impacts, such as soil type, plant growth stage and seasonality. (2) Risk assessment studies were conducted to assess potential side effects of Fos inoculation on non-target soil microorganisms.
Untersuchung alternativer Unkrautmanagementsysteme für Kulturraps unter Einbeziehung von Möglichkeiten zur Reduzierung des Auftretens von Raps als Durchwuchs
(2022) Schwabe, Sebastian; Claupein, Wilhelm
Oilseed rape is the worlds second most important oil crop after soybeans. In the course of the European Green Deal of the European Union and the associated stronger promotion of renewable energies in the future, it can be assumed that the importance of oilseed rape cultivation will continue to increase. Due to the price pressure on conventional farms in Germany, cultivation systems have been changed from an economic point of view, partly to the detriment of sustainability. As a re-sult, crop rotations often consist of a few monetarily profitable crops and the proportion of spring crops in the crop rotation is reduced. Oilseed rape cultivation is attractive from an economic point of view, and its share in the crop rotation has been increased. The intensity of tillage and mechanical weed control has been reduced. The weed control success is strongly dependent on the effectiveness of numerically limited herbicidal active agents. Due to monotonous crop rotations and the lower tillage intensity, certain weed species are pro-moted more strongly, while at the same time these are controlled with only a few herbicid-al active agents. Adapted, difficult-to-control, and in some cases herbicide-resistant weed populations develop. For this reason, the purpose of this thesis is to evaluate alternative weed management systems in oilseed rape, while also investigating options for prophylac-tic prevention of the emergence of volunteer oilseed rape as a weed in crop rotation. The objectives of this thesis were: (i) To evaluate the feasibility of hoeing as a mechanical weed control method and the application of the Clearfield® system in oilseed rape as a comparison to common, field herbicide strategies. (ii) To focus on the volunteer oilseed rape issue. Volunteers resulting from Clearfield® oilseed rape are more difficult to control chemically in subsequent crops due to inherited herbicide tolerance. The potential of differ-ent seed treatments in oilseed rape to reduce the development of secondary dormancy, and therefore seed persistence in the soil and the volunteer oilseed rape issue, was investigat-ed. Following these objectives, several field and laboratory experiments were conducted to generate data for three published scientific papers. Paper I: A two-year field trial was conducted to evaluate the performance of the Clearfield® system in oilseed rape under different management intensities compared to a more com-monly used pre-emergence herbicide system. The Clearfield® system is an alternative weed management system for oilseed rape. It is a combination of a broad-spectrum post-emergence herbicide and a Clearfield® oilseed rape variety that has tolerance to the herbi-cide. This tolerance was implemented in Clearfield® oilseed rape varieties through conven-tional, non-GM breeding techniques. Clearfield® herbicides have lethal effects on non-Clearfield® oilseed rape varieties. Paper II: An investigation was made through laboratory and field trials on the effect of ger-mination-promoting substances (nutrients and gibberellic acid) on the development of sec-ondary dormancy of oilseed rape seeds and on their persistence in the soil. Paper III: In a three-year field trial, hoeing as a weed control method was compared with a commonly used herbicide strategy. The hypotheses made in the introduction were both confirmed and refuted by the findings obtained in the trials. Hypotheses stated in paper I: (i) The Clearfield® herbicide and herbicides of a common practice pre-emergence strategy show similar efficiencies; (ii) Management intensity has an effect on weed density but does not affect yield; (iii) Herbicide strategy does not affect yield. At higher management intensities, both herbicide systems achieved comparable efficien-cies. At lower management intensities, especially in terms of seeding density and tillage, weeds were less efficiently controlled with the Clearfield®-system, and yields were par-tially lower. At higher management intensities, higher yields and lower weed emergence were observed compared to lower intensities, presumably due to better weed control by plowing and more favorable emergence conditions due to a higher tillage intensity. Hypotheses stated in paper II: (i) All tested substances reduce the induction of secondary dormancy; (ii) the tested sub-stances reduce the induction of secondary dormancy to different extents; (iii) the tested substances have an effect on the induction of secondary dormancy, regardless of whether the tested oilseed rape seeds originate from varieties with a high or low tendency, to devel-op secondary dormancy; (iv) if a variety tends to develop high secondary dormancy, its in-duction is reduced to a greater extent by the tested substances than in seeds from a variety with a low tendency to develop secondary dormancy. Most of the tested substances reduced both the induction of secondary dormancy and the survivability of oilseed rape seeds. The efficiency of the reduction depended on the type of substance and the oilseed rape variety. Substances containing gibberellic acid proved most effective, followed by micronutrient treatments and potassium nitrate. Hypotheses stated in paper III: (i) Hoeing achieves the same weed control efficiency as herbicides; (ii) regardless of whether herbicides or hoeing are used as weed control, the same oilseed rape yield can be realized. Weed biomass was higher compared to herbicide application when hoeing was used as a weed control measure. This is probably due to the weather-dependent efficiency of hoe-ing and its only partial surface applicability. Weeds emerging in or close to the seed row cannot be controlled. Nevertheless, no yield differences were found between hoeing as a weed control measure and pure chemical weed control. The competitive strength of the varieties used was most likely large enough to ensure this yield stability. Both hoeing and applying the Clearfield® system under higher management intensities re-sulted in similarly high oilseed rape yields compared to conventional herbicide strategies, although weed control efficiency was lower. As long as no hard-to-control weeds occur on a conventional farm and a common herbicide strategy effectively controls existing weeds, changing the weed management system is less beneficial. Because the Clearfield® system increases selection pressure on weeds, the occurrence of weed herbicide resistance be-comes more likely. In addition, Clearfield® volunteer canola is more difficult to control chemically in subsequent crops. Hoeing efficiency is weather dependent, weeds are only captured between rows, and area performance is lower. However, when difficult-to-control weeds increasingly minimize the efficiency of existing, conventional chemical control strategies, both hoeing and the use of the Clearfield® system in combination with a common herbicide strategy can expand weed control options and in-crease their efficiencies. When applying the Clearfield® system, strategies should be em-ployed to minimize the occurrence of Clearfield® volunteer oilseed rape in subsequent crops. It has been shown in this thesis that germination-promoting compounds, particularly gib-berellic acid, prevent the induction of secondary dormancy, as well as the ability of oilseed rape seeds to persist, and therefore, have the theoretical potential to contribute to a reduc-tion in the volunteer oilseed rape occurrence problem. Overall, both hoeing and the application of the Clearfield® system as alternative weed man-agement systems can usefully complement established methods of weed control in oilseed rape, where necessary. In addition, the use of germination-promoting compounds in oilseed rape seeds has demonstrated the theoretical potential to contribute to a reduction of volun-teer oilseed rape as a weed in crop rotations.
Untersuchungen zur pneumatischen Aufnahme von Unkrautsamen
(1998) Kahrs, Johannes; Kutzbach, Heinz Dieter
Die Erntearbeit mit dem Mähdrescher kann für die Unkrautbekämpfung genutzt werden. Die Unkrautbekämpfung, bzw. die Beeinflussung der Unkrautpopulation beim Mähdrusch kann mit unterschedlichen Geräten und Einrichtungen durchgeführt werden. Insbesondere in biologischen Betrieben sollte die Erntearbeit mit dem Mähdrescher aus ökonomischen und ökologischen Gründen genutzt werden, um Unkrautsamen von der Ackerfläche zu entfernen und damit den Unkrautsamenvorrat des Bodens zu entziehen. Eine Möglichkleit ist die Sammlung der bei der Getreidernte auf der Bodenoberfläche liegenden Unkrautsamen. Im Rahmen der vorliegenden Arbeit werden spezielle Saugeinrichtungen für die pneumatische Aufnahme von Unkrautsamen untersucht.
Weed suppression with cover crops and undersown crops in modern cropping systems
(2014) Brust, Jochen; Gerhards, Roland
The agronomic situation in Germany is characterized by a reduction of crop diversity within crop rotations, which is mainly a consequence of present economic conditions. This results in rare change between fall and spring seeded crops, combined with increasing weed populations. The integration of cover crops and undersown crops into such cropping systems could be a step to reduce the amount of herbicides during crop cultivation but also within a fallow period. The aim of this study was to determine the influence of cover crop and undersown crop cultivation on arable farming systems from the perspective of weed science. Furthermore it should be clarified in which way it is possible to integrate cover crops and undersown crops in intensive cropping systems. Within the cover crop topic this was done by the search for new cover crop species which are suitable for cultivation in Central Europe to expand the range of available cover crop species for lots of cropping situations and site conditions. Additionally the weed suppression ability of different cover crop species in fall and spring was analyzed to determine if it is possible to avoid a mechanical or chemical weed control prior seeding the next cash crop. Within the undersown crop topic the influence of different management practices on growth of undersown crop as well as growth and yield formation of the main crop was investigated. Furthermore, it was researched if it is possible to achieve a suppression of weeds by undersown crops. The conducted experiments relating the cover crop topic showed that from the new cover crop species especially tartary buckwheat, forage radish and lopsided oat are well suited for cultivation. The shoot and root growth of weeds could be effectively reduced by the successful establishment of a cover crop stand in fall. In plots of competitive cover crops like yellow mustard, oilseed radish, tartary buckwheat and lopsided oat, no further growth of weeds and volunteer cereals occurs after the first measurement in fall four weeks after cover crop planting. The weed-suppressing effect of cover crop cultivation was measurable not only in fall during growth, but also in spring after freezing of cover crops. Especially in plots of late freezing cover crop species like oilseed radish and phacelia only a very reduced plant density or even no living weeds and volunteer grains were observed. The conducted experiments relating the undersown crop topic demonstrate that it is possible to integrate undersown crops in high yielding cereal cropping systems without decreasing growth and yield formation of the main crop. During the four conducted field experiments, a reduction in grain yield was only observed when perennial ryegrass was seeded at the three leaves stage of spring wheat and grew under sufficient nitrogen conditions. The study shows that undersown crops are able to reduce weed density during main crop growth. However, the habitus of weeds was an important factor influencing the weed suppression ability of undersown crops. Undersown crops were able to reduce the density of small growing weed species such as Veronica persica while density of high-growing weeds like Chenopodium album were not affected. The experiments in this study offer that is possible to successfully integrate cover crops and undersown crops into modern agricultural systems without reducing their productivity. Furthermore it was demonstrated that due to the cultivation of cover crops and undersown crops it is possible to control the growth of weeds not only during but also between cash crop vegetation. By these methods, under certain conditions a reduction of the required amount of herbicides is possible, which can be a contribution to a more sustainable food production.