Browsing by Subject "Unkrautbekämpfung"

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Decision support systems for weed management in North China plain winter wheat production systems
(2012) Menegat, Alexander; Gerhards, Roland
The North China Plain region is on eof the major production regions for wheat and maize in China.Weed control practice in the North China Plain has changed from hand weeding towards chemical methods. This change in weed management practice is caused by a shift of labour towards the fast growing industrial sector and by steadily increasing yields which made herbicides affordable even for small scale farmers. Agriculture in the North China Plain region is characterised by a double cropping system of winter wheat followed by summer maize in one year. Due to the continuous overuse of chemical fertilizers, irrigation water and pesticides severe problems are aligned with this intensive cropping system. Especially the accumulation of pesticide residues in the food chain as well as in environmental resources becomes an increasing problem. Objective of this study is to develop a decision support system for weed management for the North China Plain winter wheat production system. Examples in Europe showed that herbicide input can significantly be reduced by implementing decision support systems. Herbicide selection, dosage and timing of application is calculated on basis of knowledge on weed-crop interaction and dose-response relationships of herbicides and weeds. The decision support systems aims to provide reliable decisions under consideration of economic and ecologic effects of herbicide use.
Effects of weeds on yield and determination of economic thresholds for site-specific weed control using sensor technology
(2014) Keller, Martina; Gerhards, Roland
Weeds can cause high yield losses. Knowledge about the weeds occurring, their distribution within fields and their effects on the crop yield is important to achieve effective weed control. The critical period for weed control (CPWC) and the economic threshold (ET) are important key concepts and management tools in weed control. While the former helps to time weed control in crops of low competitiveness, the latter provides a decision aid to determine whether weed control is necessary. This decision is generally taken at the field level. Weeds have been found to be distributed heterogeneously within fields. Site-specific weed control (SSWC) addresses this sub-field variation by determining weed distribution as input, by taking control decisions in the decision component and by providing control measures as output at high spatial resolution. Sensor systems for automated weed recognition were identified as prerequisite for SSWC since costs for scouting are too high. While experiences with SSWC using sensor data as input are still scarce, studies showed that considerable herbicide savings could be achieved with SSWC. ETs can serve as thresholds for the decision component in SSWC systems. However, the commonly used ETs were suggested decades ago and have not been updated to changing conditions since. The same is the case for the CPWC in maize in Germany. In addition, the approaches to determine the CPWC are usually not based on economic considerations, which are highly relevant to farmers. Thus, the objectives of this thesis are: 1. To test different models and to provide a straightforward approach to integrate economical aspects in the concept of the CPWC for two weed control strategies: Herbicide based (Germany) and hoeing based (Benin); 2. To determine the effect of weeds on yield and to calculate ETs under current conditions which can be used for SSWC; 3. To evaluate the use of bi-spectral cameras and shape-based classification algorithms for weed detection in SSWC; and 4. To determine changes in weed frequencies, herbicide use and yield over the last 20 years in southwestern Germany. Datasets in maize from Germany and Benin served as input for the CPWC analyses. The log-logistic model was found to provide a similar fit as the commonly used models but its parameters are biologically meaningful. For Germany, analyses using a full cost model revealed that farmers should aim at applying herbicides early before the 4-leaf stage of maize. In Benin, where weed control is mainly done by hoeing, analyses showed that one well- timed weeding operation around the 10-leaf stage could already be cost-effective. A second weeding operation at a later stage would assure profit. The precision experimental design (PED) was employed to determine the effect of weeds, soil properties and herbicides on crop yield in three winter wheat trials. In this design, large field trials’ geodata of weed distribution, herbicide application, soil properties and yield are used to model the effects of the former three on yield. Galium aparine, other broadleaved weeds and Alopecurus myosuroides reduced yield by 17.5, 1.2 and 12.4 kg ha-1 plant-1 m2 determined by weed counts. The determined thresholds for SSWC with independently applied herbicides were 4, 48 and 12 plants m-2, respectively. Bi-spectral camera based weed–yield estimates were difficult to interpret showing that this technology still needs to be improved. However, large weed patches were correctly identified. ETs derived of field trials’ data carried out at several sites over 13 years in the framework of the ’Gemeinschaftsversuche Baden-Württemberg’ were 9.2-9.8 and 4.5-8.9 % absolute weed coverage for winter wheat and winter barley and 3.7% to 5.5% relative weed coverage for maize. Overall, the weed frequencies in winter cereals were found to be more stable than the weed frequencies in maize during the observation period. In maize, a frequency increase of thermophilic species was found. Trends of considerable yield increases of 0.16, 0.08 and 0.2 t ha-1 for winter wheat, winter barely and maize, respectively, were estimated if weeds were successfully controlled. In order to evaluate the use of bi-spectral cameras and shapebased classification algorithms for weed detection in SSWC, herbicides were applied site-specifically using weed densities determined by bi-spectral camera technology in a winter wheat and maize field. Threshold values were employed for decision taking. Using this approach herbicide savings between 58 and 83 % could be achieved. Such reductions in herbicide use would meet the demand of society to minimize the release of plant protection products in the environment. Misclassification occurred if weeds overlapped with crop plants and crop leaf tips were frequently misclassified as grass weeds. Improvements in equipment, especially between the interfaces of camera, classification algorithms, decision component and sprayer are advisable for further trials. In conclusion, the derived ETs can be easily implemented in a straightforward SSWC system or can serve as decision aid for farmers in winter wheat and winter barley. Further model testing and adjusting would be necessary. For maize, the use of ETs at the field level is not suggested by this study, however the need for early weed control is clearly demonstrated. Bi-spectral camera technology combined with classification algorithms to detect weeds is promising for research use and for SSWC, but still requires some technical improvements.
Effects of woody plants and their residues on crop yield, weedsand soil carbon fractions in selected arable cropping systems
(2018) Xu, Jialu; Gruber, Sabine
Gehölze können auf Ackerflächen zu Produktionszwecken angebaut werden (z.B. Bäume zur Biomasseproduktion) oder dienen als Feldgrenzen (z.B. Hecken). Gehölzpflanzen auf Ackerflächen wirken sich dabei positiv auf die Biodiversität aus, verringern die Bodenerosion sowie die Nitratauswaschung und haben einen positiven Einfluss auf die Trinkwasserqualität. Des Weiteren tragen sie zu einer Zunahme der organischen Bodensubstanz und zur Kohlenstoffsequestrierung im Boden bei und leisten damit einen Beitrag zum Klimaschutz. Die Gehölzpflanzen selber und auch deren Rückstände wie z.B. Häckselgut von Hecken können aber auch ungewünschte Auswirkungen auf die Kulturpflanzen nach sich ziehen, die beispielsweise durch allelopathische Effekte oder durch die Konkurrenz um Ressourcen (z.B. Licht) hervorgerufen werden. In der Vergangenheit fielen Gehölzpflanzen auf Ackerflächen vermehrt der Intensivierung und Mechanisierung in der Landwirtschaft zum Opfer, während heutzutage Bestrebungen bestehen, deren Zahl zu erhalten, um Ökosystemleistungen zu sichern. Das Ziel dieser wissenschaftlichen Arbeit war, Wechselwirkungen zwischen Pflanze und Boden bei ausgewählten Gehölzen sowie deren Ernterückständen auf Ackerflächen zu untersuchen. Die vorgelegte Arbeit besteht aus vier Publikationen und umfasst Labor- und Feldexperimente, die sich zum einen mit den Effekten von Hackschnitzeln aus Heckenrückschnitt auf die landwirtschaftliche Produktion und zum anderen mit dem Vergleich einer Kurzumtriebsplantage mit anderen „Energiepflanzen“ in unterschiedlichen Anbausystemen beschäftigen. In den Untersuchungen werden relevante Aspekte zu Erträgen der Kulturpflanzen, Unkräutern und ausgewählten Bodenparametern herausgegriffen. Die erste Publikation (veröffentlicht im Agronomy Journal) beschreibt Langzeiteffekte der Ausbringung von Hackschnitzeln von Hecken (hauptsächlich Acer pseudoplatanus L., Prunus avium L., Prunus padus L., Salix caprea L., Ligustrum vulgare L., und Fraxinus excelsior L.) auf den Ertrag und den Unkrautbesatz auf einer ökologisch bewirtschafteten Ackerfläche. Hierfür wurden Daten eines 16-jährigen Versuchs auf der ökologisch bewirtschafteten Versuchsstation Kleinhohenheim in Südwestdeutschland gesammelt. Untersucht wurde der Effekt von Hackschnitzelmulch (HSM) auf eine typische Fruchtfolge (Getreide, Leguminosen und Ackerfutter). Die Hackschnitzel stammten vom Rückschnitt der Hecken des Betriebs und wurden jährlich in drei verschiedenen Mengen ausgebracht (0, 80 und 160 m3 ha-1). HSM führte zu einer Reduktion des Unkrautbesatzes um 9 % im Frühjahr, wobei höhere Ausbringungsmengen im Vergleich zu niedrigeren generell in geringerem Unkrautbesatz resultierten. Der Einfluss auf den Ertrag war statistisch nicht signifikant, jedoch wurden über die Versuchszeit tendenziell sinkende Erträge auf mit HSM behandelten Parzellen gegenüber der Kontrolle beobachtet. Die unkrautunterdrückende Wirkung des HSM könnte auf verschiedenen Effekten beruhen, nämlich der mechanischen Behinderung des Auflaufens von Unkräutern, einer geänderten Bodentemperatur, einer reduzierten Stickstoffverfügbarkeit durch die Gabe von Material mit vergleichsweise weitem C:N-Verhältnis sowie allelopathischen Effekten. Hackschnitzel können daher zwar zur Unkrautkontrolle auf Ackerflächen verwendet werden, es müssen jedoch potentiell ungewünschte Effekte auf die Kulturpflanzen berücksichtigt werden. Die zweite Publikation (eingereicht bei Seed Science Research) basiert direkt auf der ersten und beschäftigt sich mit möglichen allelopathischen Effekten von HSM und deren Einfluss auf die Samenkeimung unter Laborbedingungen. Getestet wurden die Auswirkungen wässriger Extrakte von Hackschnitzeln der Salweide (Salix caprea L.) und der Gewöhnlichen Traubenkirsche (Prunus padus L.) auf die Keimung von Raps (Brassica napus L.) und Weizen (Triticum aestivum L.). Ziel dieser Arbeit war die Entwicklung einer standardisierten Extraktionsmethode, wobei die Trocknung (Gefriertrocknung, Ofentrocknung mit 25, 60 oder 105 °C), das Mahlverfahren, das Holz-Wasser-Verhältnis bei der Extraktion (HWV; 1:10, 1:15 oder 1:20) und das Ausgangsmaterial (Rinde oder Kernholz) variiert wurden. Die Extrakte aus der Gefriertrocknung und die des ungetrockneten Holzes führten nach zwei Wochen zu der geringsten Keimrate (<6 %) bei beiden Kulturarten. Die ofengetrockneten Varianten besaßen eine höhere Keimrate von 12 bis 53 %. Die Keimrate von Raps lag bei einer hohen HWV (1:10) mit Extrakten aus gemahlenen Hackschnitzeln der Gewöhnlichen Traubenkirsche bei 26 % und damit signifikant niedriger als mit Extrakten aus ungemahlenem Material (49 % Keimung). Weizenkörner keimten unter diesen Bedingungen in geringerer Anzahl als Raps, aber die Keimung war mit Extrakten aus gemahlenem Material (1%) auch geringer als mit Extrakten aus ungemahlenem Material (19 %). Der Effekt der Keimungsunterdrückung stieg mit erhöhtem HWV bzw. höherer Konzentration der Extrakte. Die Keimraten betrugen durchschnittlich für HWV 1:20 86 %, für HWV 1:15 71 % und für HWV 1:10 35 % mit gemahlenen Hackschnitzeln. Aus der Rinde gewonnene Extrakte führten zu einer signifikant geringeren Keimrate (<4 %) als die des Kernholzes (<88 %). Die effektivste Methode zur Erhaltung offensichtlich allelopathisch wirksamer Verbindungen war die Kombination aus gemahlenen Hackschnitzeln aus Rindenholz, Gefriertrocknung (-50 °C) und einem hohen HWV. Diese hatte den größten Effekt auf die Unterdrückung der Keimung. Die Ergebnisse aus dieser Publikation können zur Untersuchung weiterer Gehölzarten angewandt werden und bieten eine Grundlage für die Auswahl geeigneter Substrate mit einem möglichst hohen allelopathischen Potential zur Unterdrückung von Unkraut. Die dritte Publikation (in Vorbereitung) beschäftigt sich mit der organischen Substanz (OS) beim Anbau mit Gehölzen zur energetischen Nutzung im Vergleich zum Anbau annueller Energiepflanzen auf Ackerland. Untersucht wurde ein 12-jähriger Dauerversuch auf der Versuchsstation Ihinger Hof in Südwestdeutschland mit einer Weiden-Kurzumtriebsplantage (Salix schwerinii E. Wolf x viminalis L.) und einer 12-jährigen Maismonokultur (Zea mays L.). In diesem Versuch wurden Bodenproben im Bereich 0 –10 cm und 10 – 20 cm gezogen. An jeder Probe wurden im Labor eine Dichtetrennung sowie eine Fraktionierung nach Korngröße durchgeführt, und der Kohlenstoffgehalt jeder Fraktion bestimmt. Die Dichtefraktionierung resultierte in einer leichten Fraktion (<1,8 g cm-3), die sich aus freier partikulärer und in Bodenaggregaten eingeschlossener OS „occluded- particulate organic matter“ (f-POM und o-POM) zusammensetzte sowie der schweren Fraktion, bestehend aus drei Klassen verschiedener Partikelgrößen: Sand (63-2000 μm), Lehm (2-63 μm) und Ton (<2 μm). Generell fanden sich höhere Gehalte an OS in der oberen Bodenschicht unter Weiden (1,39 %) als im Maisanbau (1,13 %). Im Boden unter Weiden war die leichte Fraktion (f-POM und o-POM) um 154 % höher als beim Maisanbau. Grund dafür war der kontinuierliche Zufluss von Streu und von Wurzelresten sowie die fehlende Bodenbearbeitung. Ebenso war das C:N Verhältnis der OS in den Sandfraktionen unter Weide (28, 24 und 16) höher als unter Mais (23, 18 und 9). Die Ergebnisse deuten auf einen langsamen Umsatz von OS und damit auf ein höheres Kohlenstoffsequestrierungspotential unter Weiden in Kurzumtriebsplantage als beim Maisanbau hin. Die vierte Publikation (veröffentlicht im Agronomy Journal) nutzt denselben 12-jährigen Feldversuch wie die dritten Publikation. Es erfolgte eine Bewertung des Biomasse- und des Bruttoenergieertrags von sechs annuellen und perennierenden Energiefruchtfolgen mit verschiedenen Stickstoffdüngungsstufen. Die annuellen Systeme bestanden aus Mais in Monokultur mit reduzierter Bodenbearbeitung; einer Fruchtfolge mit Raps (B. napus L. ssp. oleifera) – Weizen (Triticum aestivum L.) – Triticale (Triticale x triticosecale Wittmack) mit wendender bzw. keiner Bodenbearbeitung. Die perennierenden Systeme umfassten eine Kurzumtriebsplantage mit Weiden (S. schwerinii E. Wolf x viminalis L.), Miscanthus (Miscanthus x giganteus Greef et Deu.) und Ruthenhirse (Panicum virgatum L.). Für jedes Anbausystem wurden drei Stickstoffdüngungsstufen (0, 50 und 100 % der praxisüblichen Düngemenge) etabliert. In Mais wurde im Mittel der höchste jährliche Biomasseertrag festgestellt (18,5 Mg ha-1), gefolgt von Miscanthus (18,3 Mg ha-1) jeweils bei einem N-Düngeniveau von 100 %. Ohne Stickstoffdüngung lag der jährliche Biomasseertrag bei Miscanthus mit 13,6 Mg ha-1 am höchsten. Das hohe Ertragsniveau konnte bei beiden Kulturen über die 12-jährige Versuchslaufzeit nur mit der höchsten N-Düngerstufe gehalten werden. In den Fruchtfolgen und bei Rutenhirse sanken die Erträge über die Jahre auch mit hoher Stickstoffgabe. Je geringer die Stickstoffdüngung ausfiel, desto stärker war der Ertragsrückgang. Die Weiden in Kurzumtriebsplantage zeigten unabhängig von der Stickstoffdüngung und der Versuchslaufzeit im Mittel gleichbleibende Erträge von 11 Mg ha-1. Offenbar ist die Stickstoffdüngung für Weiden in Kurzumtriebsplantagen im Vergleich zu den anderen untersuchten Kulturen und Anbausystemen ein weniger wichtiger Produktionsfaktor. Das Ausbringen von Hackschnitzel von Hecken auf Ackerflächen und der Anbau von Gehölzpflanzen (Weide in Kurzumtriebsplantage) zeigten Effekte im oberirdischen Pflanzenaufwuchs und hatten Auswirkungen auf die Bodeneigenschaften. Gewünschte Auswirkungen der Managementmaßnahmen waren (i) die Verringerung des Unkrautbesatzes, (ii) der geringe Stickstoffinput für eine zufriedenstellende Produktivität von Weiden in Kurzumtriebsplantage, und (iii) und die Erhöhung der OS (Kohlenstoffsequestrierung). Unerwünschte Effekte äußerten sich in der tendenziellen Reduktion der Biomasseproduktion der Kulturpflanzen Wie die Studie zu Extrakten aus den Hackschnitzeln zeigt, scheinen tatsächlich allelopathische Effekte eine mögliche Ursache für die Unkrautunterdrückung bei der Hackschnitzelapplikation zu sein. Diese oder ähnliche Effekte könnten auch nach der Rodung von Kurzumtriebsplantagen auf die Nachfrüchte auftreten, z.B. aus Rückständen von Wurzeln und Stamm. Weiterhin könnte beim Erhalt von Heckenbiotopen auch mit einer Kohlenstoffsequenzierung gerechnet werden, ähnlich wie es bei den Weiden in Kurzumtriebsplantage gezeigt wurde. Die günstigen Effekte des Anbaus von Gehölzen könnten Landwirte motivieren, Gehölzpflanzen auf ihren Ackerflächen zu belassen bzw. zu etablieren und die Ökosystemleistungen auf dem Betrieb zu erhöhen. Weiterführende Forschung könnte darauf abzielen (i) technische Lösungen für eine praktikable Hackschnitzelausbringung zur Unkrautbekämpfung zu finden, (ii) die allelopathisch wirksamen Substanzen von Gehölzen zu identifizieren und zu isolieren und so gegebenenfalls Grundlage für eine neue Generation von Herbiziden zu schaffen, (iii) Langzeitfolgen von Ernterückständen nach dem Anbau von Kurzumtriebsplantagen auf die nachfolgenden Kulturen zu untersuchen, und (iv) Studien zur C-Sequestrierung unter naturnahen Hecken vorzunehmen.
Entwicklung eines neuartigen Selektivhacksystems zur Unkrautkontrolle in Zuckerrüben
(2022) Heinrich, Stefan; Köller, Karlheinz
The production of organic sugar beets is one of the biggest challenges in organic farming. Due to its slow youth development, it is less competitive with seed weeds like white goosefoot, knotweed, or cockspur. The control in organic farming is mainly done mechanically with the help of hoeing systems between the rows and with harrow and finger weeders within the rows. The brittleness in the youth stages doesn’t allow an aggressive deployment of the in-row methods mentioned before, so the results stay far behind the expectations. To raise the yields and to make a harvest at least possible a manual removal of the weeds is essential. The effort on manual labor is settled between 50 to 250 hours per hectare. To reduce the costs for man-ual weeding some attempts were made to use automatic weeding systems from the vegetable production. Due to the small distances between the plants and the missing head start of the crop, the losses of the used systems were higher than the generated benefits. The main rea-sons for the fail belong to the plant detection system and the tool design. State-of-the-art tech-nology uses mainly color information and geometrical measurements to separate the plants from each other. Most of the tools use simple systems which open in front of a plant and close behind it. The driving speed is limited throughout the swing-in process. None of the tools that have been used so far have no “zero-intervention”, so the risk of the plants being buried in-creases in proportion to the driving speed. In the present dissertation, new concepts for online plant recognition are first developed. The detection of sugar beet is one of the most complex tasks in mechanical weed control. Due to the small distance between the plants and the special growth habits a precise detection of the center point is challenging. Common systems out of the industrial image processing field can-not be used directly, because of the small similarities between the plants. To get successful detection results important attributes like the distinctive leaf blade must be worked out. The main task is to develop a fully practical proofed selective weeding system. Therefore an evalu-ation between an autonomous platform and a tractor-mounted system has to be made. Due to the fact of the low power supply, it was decided to develop the tractor-mounted system. For the start, a common front weeding system is used to build the prototype. It is first used to collect image data. In the following steps, the platform is required to integrate the first in-row weeding tools. Starting with the results from the previous master thesis classical image recognition methods are used to develop different approaches for the detection of the center points. The approaches mainly differ in the plant growth stages. Until the two-leaf stage, binary operators deliver good results. Starting with the four-leaf stage, the new edge detection system for local-izing the centerline of the leaf reaches an accuracy of up to 20 mm. The single plant detection system achieves recognition rates from 50 % to 98 % depending on different growth stages and lighting conditions. Thanks to the grid seeding system it was possible to reach excellent detection rates even under a high degree of weed cover and harsh conditions. By sowing the plants in a triangular arrangement, it was possible to reduce the plant losses below 1 %. To bring the detection results to the ground the currently developed rotor weeding system from the University of Bonn was used as a starting point for developing new kinematics. It achieves throughout the hydromechanical contact pressure control a better ground contour following. It is also significantly less susceptible to difficult working conditions. Due to the inclination of the rotor, the so-called “zero-intervention” could be developed. Due to the adapted cutting angle to the row, the driving speed is completely compensated. This prevents the crops from covering with soil. The tool is hydraulically driven to create a robust and inexpensive platform. It should also be possible to use the components in future serial production. The cascade controller from the rotor achieved an angular accuracy below 0,7°. The plant positions primarily detected for the in-row system could also be used for the realization of a row guidance system. For this purpose, an active implement steering was designed in addition to the automatic tractor steer-ing system. This improved the guiding behavior of the front weeding system. In order to achieve the highest possible regulating effect for every growth stage, disc colters are used in combination with optional angled shares. In later stages goosefoot shares with optional wings can be used to reach a higher pile effect. Also, the in-row system is fully integrated into the tine carrier to obtain a compact unit. By linking the information from the sowing technology and the image processing, it has been possible to develop a highly robust and fail-safe system for mechanical weed control in organic sugar beet.
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.
Pflanzenbauliche Untersuchungen zum ökologischen Anbau von Körnerleguminosen an sommertrockenen Standorten Südwestdeutschlands
(2007) Poetsch, Jens; Claupein, Wilhelm
Grain legumes, as nitrogen fixing crop, protein rich animal feed and marketable product are of great importance for organic agriculture. Due to staged abolition of the possibility to add non-organic products in organic animal feeding, the EU?s demand for organically produced protein feed is further increasing. Field bean (Vicia faba) and field pea (Pisum sativum) are large-scale crops but feature a limited feeding value. Lupin species (Lupinus spp.) excel by protein contents of up to 40% in the seed and higher protein value. At warmth favoured locations in southwestern Germany the valuable soybean (Glycine max) can be grown successfully and obtain above-average proceeds in natural food industry. Constraints of yield stability of grain legumes result amongst other things from frequently high weed infestation in organic cropping systems and suboptimal water supply at summer-dry locations. For lupins, moreover, particular soil requirements and the seed-borne fungal disease anthracnosis are problematic. Nitrogen residues after harvest are relevant for subsequent crop as well as groundwater protection. The presented work aimed at defining preconditions and developing cropping strategies to optimise yield stability and level of organically grown grain legumes with a main focus on summer-dry locations, to increase diversity of cultivatable crops and provide information on disposition of nitrogen residues. For this purpose from 2003 to 2005 trials at several locations as well as in greenhouse and laboratory were accomplished. Field trials on organic weed control in soybean as well as white and narrow-leafed lupin (Lupinus albus und L. angustifolius) were conducted at organically managed commercial sites in the upper rhine valley. At the same time agronomic measures for optimisation of competitiveness and machinery implementation were varied. Early high soil coverage and crop height contributed considerably to grain legumes? competitiveness. Delayed sowing at elevated temperatures supported rapid juvenile development and allowed for pre-sowing weed control. At optimum sowing date these effects may be used without yield depression or maturity problems. Reduced row distance was beneficial for optimum space utilisation and early crop closure, but effectiveness of mechanical means was highest at high row distance and large areal proportion for interrow cultivation. As an optimum compromise for grain legumes row distances of 30 - 35 cm are recommended. Optimum impact of mechanical means against weeds was achieved by combining interrow cultivation with harrow or fingerweeder. Forgoing interrow cultivation may be considered in strongly competitive crops like field bean. Lupin species appeared rather poor in competitiveness compared to other crops. Field trials on effects of cultivar and cropping strategy on overwintering and yield performance of autumn-sown field bean, field pea and white lupin were conducted at three locations. Summer drought caused substantial yield advantages of autumn-sown compared to spring-sown cultivars due to superior water supply at earlier flowering. With sufficient water supply a head start was not yield effective. Differing coincidence with pests and diseases could account for advantages (head start on aphid infestation) or disadvantages (fungal infections during winter period) of autumn-sown cultivars. Overwintering was excellent for winter field bean and good for winter field pea. For winter white lupin further trials are required. Temperatures down to -12°C were well endured by all of the three crops. The most important cropping parameter was the sowing date. Winter field bean permitted a relatively wide sowing window. Winter white lupin required strong development before winter and preferably early sowing. Sowing date of winter field pea presented an optimisation problem, because sowing too early leads to overdevelopment and reduced cold-tolerance, while sowing too late may reduce yield potential. Optimum sowing dates for southwestern Germany according to experimental results are in the range of early September (winter white lupin), mid-October (winter field bean) and late October (winter field pea). Water use efficiency may gain significantly in importance in the future. A two-year trial on cultivation prospects and yield performance of the notably drought tolerant chickpea (Cicer arietinum) in the upper rhine valley resulted in successful crop development, but problems with empty pods and inadequate grain quality. Further trials are considered promising. A field trial with white and narrow-leafed lupin confirmed that anthracnosis of lupin spreads less rapidly and yield effectively at summer-dry locations, and narrow-leafed lupin frequently stays unaffected. Laboratory studies for optimising detection methodology of the causative organism Colletotrichum lupini showed advantages of using sectioned petri dishes (quad plates), which confined propagation of disturbing organisms. A trial on seed storage under different temperatures, seed moisture contents and CO2-atmosphere produced no distinct treatment effect, but could confirm the general decrease of seed infection by storage. According to literature hot air (approx. 4 days at 65°C) also reduces seed infection effectively. Thus, storage or hot air treatment of basic seed and propagation at summer-dry locations appear as a viable over-all strategy. Difficult soil requirements of white and narrow-leafed lupin were studied by a pot trial as well as a comprehensive literature analysis. It is concluded that the so-called lime chlorosis is caused by HCO3--induced inactivation of physiologically relevant Fe(II) in the plant. Accumulation of HCO3- is basically caused by insufficient soil aeration and promoted by the presence of lime in the clay fraction. Furthermore, especially in narrow-leafed lupin, disturbances of root development are caused by high Ca-content or high and at the same time strongly buffered pH of soil solution. These conditions are often but not necessarily caused by lime. Analyses of harvest residues and soil were consulted for estimation of nitrogen dynamics. Immobilisation due to degradation of residues with high C:N ratio as well as uptake by catch crops contributed substantially to nitrogen conservation. Risk of leaching is predominantly site dependent. The over-all nitrogen balance of grain legumes when exporting the seed may be low or even negative. In conclusion, results of the presented work indicate that site adapted cropping systems with agronomic measures in the areas of crop rotation, choice of cultivar, sowing date or space allocation can still contribute considerably to yield stability in organic cultivation of grain legumes.
Teilschlagspezifische Unkrautbekämpfung durch raumbezogene Bildverarbeitung im Offline- und (Online-) Verfahren (TURBO)
(2006) Oebel, Horst; Gerhards, Roland
Georeferenced application maps (TURBO) is presented. The system was applied and analysed on agricultural fields from 2004 to 2005. The results can be summarized as followed: For online image acquisition bi-spectral cameras were developed which took homogeneous grey scale pictures with a strong contrast using a combination of two spectral channels in the near infrared and the visible spectrum. Three bi-spectral cameras were mounted in front of a prototype carrier vehicle. Using an automatic control of the exposure time, well focused pictures of weeds in cereals, maize, sugar beets, peas and oil seed rape were taken at a speed up to 10 km/h and stored together with their GPS coordinates. Under changing light conditions, bi-spectral images were free of faults. Stones, mulch and soil were not illustrated. The picture quality showed a clear improvement compared to current image analysis technologies using colour and infrared cameras in plant production. The geometric resolution of the cameras was sufficient for creating application maps. With a size of 0.014 m² per picture weed seedlings were representatively assessed. The dense grid of 3.500 sampling points per hectare allowed an efficient detection of weed distribution within agricultural fields. The procedure of shape analysis allowed precise identification of weed species in a speed of 20 images per second. The classification rate of unclassified plants using Fuzzy Logic or the principle of minimum distance was between 73 % (malt barley) and 85 % (oil seed rape). The calculation of discrimination functions to separate crops and weed classes by shape parameters allowed a better classification of unknown plants and increased the classification rate to 88.4 % (sugar beets) and 94 % (malt barley). Characteristic shape features of 45 weed species in the growth stages BBCH 10 to BBCH 14 were stored in a database and the classification of weed species in malt barley, maize and sugar beets was studied using discrimination analysis. In growth stage BBCH 10 weed species could be differentiated on average by 70 %. Crops were accurately differentiated from broadleaved weeds and grass weeds. Joining weeds species (BBCH 10) in the classes broadleaved weed species, grass weeds, Galium aparine and crop resulted in correct classification of 83 % in malt barley to 96 % in maize. With manual, GIS-based and image analysis sampling methods treatment maps for three weed species classes were created for site-specific weed control in cereals, sugar beet, maize, oil seed rape and peas on a total of 138 ha. Economic weed threshold were used as a decision rule for chemical weed control. Herbicides were only applied when the economic weed threshold was exceeded. Above the economic weed threshold the herbicide dosage was varied from 70 % to 100 % depending on the density of weed species. Herbicide application was performed with a newly developed multiple sprayer. The sprayer integrates three conventional sprayers on one machine including three separated hydraulic circuits, boom section control (3 m), dGPS for real time location and a central control unit. During application the on-board computer loading a georeferenced application maps was linked to the spray control system for precise application of up to three different herbicide mixtures. Herbicide savings using site-specific weed control depended on the cultivated crop, weed species composition and weed infestation levels. On average 47 % of herbicides for grass weeds and 35 % for broad-leaved weeds were saved. Herbicide use to control Galium aparine and Cirsium arvense was reduced by 71 %. The efficacy of site-specific weed control was documented by manual weed sampling before and after post emergent herbicide treatments. It ranged from 71.8 % to 98.8 %. Weed infestation level did not increase in the following crops. First results with yield mapping of experimental fields revealed that site-specific weed control did not cause yield reduction. On contrary, in cereals higher yields were observed at locations where no herbicides were applied. However, further studies are needed to prove this hypothesis. The economic evaluation of site-specific weed control over two years on practical farm sites showed that site-specific weed control was profitable. The average savings for herbicides were 27.61 ?/ha. This resulted in an average profit of 11.35 ?/ha using the system for site-specific weed control.
Understanding the role of plant growth promoting bacteria on sorghum growth and biotic suppression of striga infestation
(2014) Mounde, Lenard Gichana; Sauerborn, Joachim
Witchweeds (Striga sp.) are parasitic weeds of great agricultural significance, parasitizing the roots of their hosts. Striga, like all other root parasitic weeds, drain essential organic and inorganic resources from their hosts leading to poor crop development and low yield. In Africa, about 50 million ha in over 30 countries are infested by Striga spp. causing grain loss of cereals. Estimated yield losses of maize, sorghum, millets and upland rice are between 30 and 90%. The parasite, therefore, is ranked as the leading biotic constraint to cereal production in the continent. Plant growth promoting rhizobacteria (PGPR) are promising components for integrated solutions to agro-environmental problems because inoculants possess the capacity to promote crop growth and reduce the population of deleterious microbes in the rhizosphere. Although there are numerous studies on crop growth promotion and biological control of diseases, weeds, nematodes and parasitic weeds using PGPR, little is known about the potential of some Bacillus subtilis, B. amyloliquefaciens and Burkholderia phytofirmans strains in sorghum growth promotion and resistance against Striga infection. The main objective of the study was to assess the effect of B. subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans PsJN on growth promotion of sorghum crop and suppression of Striga development, thus providing a basic understanding on the sorghum-PGPR-Striga interaction. This study opens with an elaborate review of the state-of-the-art knowledge on the tripartite interactions between Striga, sorghum and different species of PGPR. Prior to this, bipartite relationship between sorghum and Striga, PGPR-sorghum and PGPR-Striga are reviewed with a focus on understanding Striga impact on sorghum, sorghum defence responses to infection, plant growth and disease suppression benefits by PGPR on sorghum, and the effect of PGPR on Striga development. Knowledge gaps in both bipartite and tripartite relationships are described, and future research recommendations given. A key recommendation from the review is to conduct experiments under controlled environmental conditions using Bacillus subtilis, B. amyloliquefaciens and Burkhoderia phytofirmans strains in order to understand their relationship with sorghum and Striga at bipartite and tripartite levels. Petri dish bioassays and root chamber experiments under controlled conditions were conducted at the Institute of Plant Production and Agroecology in the Tropics and Subtropics, University of Hohenheim between 2012 and 2014. B. subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans strain PsJN inocula and their corresponding cell culture supernatants were evaluated for their growth promotion potential on sorghum and suppressiveness on Striga development. Sorghum root exudates and synthetic stimulant GR24 were used to induce Striga seed germination. Bacillus subtilis Bsn5 supernatant, which showed the greatest inhibitory activity on Striga germination and radicle elongation, was separated by ethyl acetate into lipophilic and hydrophilic phases. The purpose of this extraction was to try and identify the polarity of the inhibitor. Protein composition by mass spectrometry (MS) was also done on the supernatant with a view of establishing the presence of peptides because peptides have been associated with Orobancheceae germination and radicle inhibition in previous studies. In addition, determination of plant growth hormones in bacteria supernatants was also conducted using Radio-Immuno-Assay (RIA) in order to relate PGPR hormone production and sorghum growth enhancement. Burkholderia phytofirmans PsJN significantly (<0.05) induced a higher vigor index (VI) on sorghum seedlings (>18,000) compared to other PGPR and control treatments. The lowest VI (7626) was recorded in seeds inoculated with Bacillus amyloliquefaciens FZB42. Complete Striga germination inhibition (0% germination) occurred in seeds exposed to all PGPR inocula suspended while the highest germination (>60%) occurred in control treatments (10% Luria Bertani (LB) + GR24 and sterile distilled water (SDW) + GR24). The effect of bacterial supernatants on the germination percentage and radicle length of Striga seeds was also significantly (<0.05) different among treatments. The least germination (7.4 %) was observed in Bacillus subtilis Bsn5 + GR24 while the highest (66 %) was observed in SDW + GR24 control. Bacillus subtilis Bsn5 supernatant produced the lowest mean radicle lengths (0.1 mm) while the highest radicle lengths were observed in SDW + GR24 (2.2 mm). Therefore, Bacillus subtilis Bsn5 supernatant was selected for further investigation of compounds causing inhibition of Striga germination and preventing radicle elongation. The supernatant was separated into hydrophilic and hydrophobic fractions using ethyl acetate. Each fraction was then prepared in 1%, 25%, 50%, 75% and 100% concentrations before being evaluated for their inhibitory activity in Striga germination and radicle elongation. The highest germination percentage (63%) and radical length (2.9 mm) was observed in SDW + GR24 control treatment. The ethyl acetate (lipophilic) fraction at both 100% and 1% concentration + GR24 produced a germination percentage of >40% which was similar to 10% LB + GR24 and ethyl acetate + GR24 controls. There was complete inhibition of Striga seed germination after exposure to either Bacillus subtilis Bsn5 supernatant + GR24 or 100% hydrophilic fraction of the supernatant + GR24. However, at 25% and 1% concentration + GR24, Striga germination percentage increased to 34% and 49%, respectively. Light microscopy examination of Striga radicles exposed to Bacillus subtilis Bsn5 supernatant + GR24 revealed that stunting of the radicles was due to reduction in cell sizes at the radicle elongation zone. Extended agar gel assays (EAGA) experiments showed a similar trend of results with B. subtilis Bsn5 showing the highest inhibitory activity on Striga germination and radicle elongation compared to other PGPR and control treatments. Results from root chamber experiments demonstrated significant (p<0.05) differences in biomass production between Striga-free and Striga-infected sorghum. Total biomass yield in uninoculated Striga-free plants was 40% higher than uninoculated Striga-infected sorghum plants. Bacillus amyloliquefaciens FZB42, B. subtilis GBO3 and Burkholderia phytofirmans PsJN inoculated Striga-free sorghum showed a 75%; 142% and 158% increase in biomass yield, respectively, compared to uninoculated Striga-free sorghum. There were no significant differences in biomass yield observed between inoculated and uninoculated Striga-infected plants. All PGPR supernatants and 10% LB media showed production of phytohormones cytokinin, IAA, GAs and ABA. Cytokinin content in PGPR supernatants was significantly (>0.05) higher than blank 10% LB control media. There was a significant negative correlation (r= -0.96) between IAA and cytokinins. However, there was no significant positive correlation between any phytohormone and sorghum plant height, SPAD values, biomass production, Striga germination, attachment and tubercle death. Finally, this study shows that Bacillus subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans PsJN might accelerate sorghum growth and suppress key stages of Striga development under laboratory conditions. Greenhouse and field experiments are recommended to better understand these interactions under natural conditions where other biotic and abiotic factors come into play. These findings could contribute to a better understanding of sorghum and beneficial bacteria interactions and provide novel information of the long-term effects of a PGPR on sorghum development, opening new avenues for Striga control and sustainable, ecofriendly sorghum production.
Unkrautbekämpfung in Zuckerrüben - Ermittlung der Kritischen Periode
(2003) Kobusch, Henner; Hurle, Karl
Early leaf stages of sugar beet are very sensitive to weed competition, which is a major reason for the absence of thresholds for weed control in sugar beet. In combination with non-selective herbicides, the use of herbicide resistant sugar beets appears to allow the control of weeds at a later date than usual applications of common selective herbicides. Therefore, it is necessary to know the critical period, in which the crop should be weed free in order not to loose yield. The influencing factors of the critical period are the moment until weed can be tolerated (beginning of the critical period) and the moment after weed can be tolerated (end of the critical period). The primary objective of the present work was the establishment of a parameter, which would allow a determination of the critical period independent of location and season. Therefore, triannual field trials were carried out at three different sites in the Ukraine and in Stuttgart-Hohenheim in order to evaluate the suitability of different parameters. In addition, by use of a glufosinat resistant sugar beet transformant, the practicability of the critical period was investigated. Application of the critical period and moreover the definition of a general period threshold requires a reference value defining the beginning and end of the critical period which is both independent of location and season. The primary aim of this work was to establish a parameter, which fulfills this condition. All parameters relate to the growth of sugar beet or of the weed quantify their interaction. The following parameters were investigated: the leaf stage of the sugar beet, the weed and sugar beet coverage level, the relative weed coverage, the temperature sum and the intensity of weed shading of the beets. The investigation took place at three separate sites in the Ukraine and in Stuttgart-Hohenheim enabling the effect of different sites to be taken into account. A uniform sugar beet leaf stage until and after weeds could be tolerated was not found. The leaf stage until weeds could be tolerated varied between the 2 and 10 leaf stage. Similarly the leaf stage after which the weeds could be tolerated varied between the 2 and 12 leaf stage of the beet. A uniform and therefore location and year-independent degree of sugar beet coverage and weed coverage relating to leaf stage was not found at the beginning of the critical period at the Hohenheim site (1999 and 2000) and Poltava (1999) in the Ukraine. The degree of weed cover varied at the beginning of the critical period between 96.7% and 66.5% in Hohenheim. The same applies to the degree of sugar beet coverage which varies between 5.3% and 15%. The difference between the two levels of coverage is almost completely compensated by the parameter relative weed coverage. At the Hohenheim site it only varied between 94.8% and 84.5%. The minimum value was found at Poltava with 83.8%. On this basis, a maximum relative weed coverage of 83 % can be tolerated without significant yield loss. Herewith, a decisive parameter is defined as a measure for timing weed control in sugar beets. However, an important requirement is the availability of efficient control methods at this certain point of time. In a further step an attempt was made to apply the critical period in relation to the leaf stage of the beet by using a glufosinate resistant sugar beet transformant. In no trail it could be waited with glufosinate applications until the beginning of the critical period. The latest leaf stage, when glufosinate application had to start in Poltava and Vinnitsa was the 6-leaf stage, whereas the critical period began at the 10- or 12-leaf stage. A limiting factor for the definitive application of the beginning of the critical period was shown in the field trials by a decreasing tolerance of the glufosinate resistant transformant at ever later leaf stages of beet development. Prediction model investigations confirmed this correlation. In addition to the effect of the leaf stage the effect of weather conditions was also apparent. The increase in air humidity from 50 % to 80 % led to an increase in NH3 concentration in the resistant transformant, regardless of its leaf stage. NH3 is found in non-resistant plants due to the inhibition of glutamine-synthetase by glufosinate, which leads to cell death. The largest increase in NH3 when the air humidity was increased from 50 % to 80 % occurred at the youngest leaf at the 6-leaf stage. In addition to the dependency of NH3 concentration on leaf stage the effect of leaf age was also apparent. Concluding, the control of weeds, related to the leaf stage of glufosinate resistant sugar beet, has to be done before the critical period begins. Unfortunately, technologies, which offer the possibility to control weeds by an integration of the critical period, are so far not available.