Institut für Phytomedizin

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A study of integrated weed control strategies for establishing soybean (Glycine max L. MERR.) in the German production system
(2017) Weber, Jonas Felix; Gerhards, Roland
Soybean (Glycine max L. MERR.) has expanded to become one of the most traded agriculture products worldwide in recent decades. Europe is one of the primary importing regions; however, the dependence on soybean imports has been critically assessed by the public. To reduce the dependency on soybean imports, increased local soybean production should be favoured. In addition to environmental conditions, weeds are a major limiting factor for soybean yield under German climate conditions. Weeds can be successfully controlled with herbicides, although crop injury frequently occurs after application. Sensor-based screening would be helpful for a rapid evaluation of cultivar tolerance to herbicide application. Alternatively, mechanical weed control strategies can be applied. Since soybean production is currently introduced to the regional crop production, weed control efficiency of conventional mechanical tools (e.g., hoeing and harrowing) have to be evaluated. By using automatic guiding systems intra-row elements could be utilised to increase the weed control efficiency of mechanical hoeing. Other than that, agronomical practices such as the tillage system or cover crops influences the occurrence of weeds. The most common practise worldwide for soybean cultivation is the no-tillage system, which has not yet been investigated under local conditions. Therefore, different weed control strategies in soybean production were investigated according to the following major objectives of this thesis: - Detection of crop injury by herbicides using a chlorophyll fluorescence imaging sensor for different soybean cultivars. - Evaluation of the conventional mechanical strategies of hoeing and harrowing in soybean. - Examination of the weed control efficiency in inter- and intra-row areas using RTK-GNSS precision steering and an optical camera guiding system for mechanical weed control in soybean. - Evaluation of the efficiency of ‘tillage’, ‘reduced tillage’ and ‘no- tillage’ cultivation systems and the influence of cover crops on weed suppression in local soybean production. The Imaging-PAM-sensor based on chlorophyll fluorescence imaging was utilised to investigate the response of different soybean cultivars to the application of herbicides. The measurements indicated significant differences with respect to injury to the cultivars after herbicide application. Herbicides containing the active ingredient ‘metribuzin’ resulted in significant differences in the level of crop injury depending on the cultivar. The active ingredients ‘dimethenamid’ and ‘clomazone’ resulted in less injury, independent of the cultivar. The PAM-sensor was able to detect stress symptoms 3 to 7 days before visual symptoms appeared. An investigation of hoeing and harrowing, which are conventional mechanical techniques for weed control, showed 78% and 72% weed control efficiency, respectively. In further experiments, the results of precision steering systems using RTK-GNSS and an optical camera guiding system additionally equipped with intra-row elements (e.g., finger weeders) were compared with the results of conventional hoeing. Mechanical weed control using automatic steering technology and an intra-row element (finger weeder) reduced the weed density by 89% compared with 68% in the conventional hoeing system. With respect to crop yields, statistical benefits of precision steering were not observed. However, the driving speed could be increased from 4 km h−1 in the conventional hoeing system to 10 km h−1 using the automatic steering systems. In an additional experiment, two cover crops species, rye (Secale cereale L.) and barley (Hordeum vulgare L.), were grown for preventive weed control in soybean production. The cover crops were transformed into a mulch layer using a roller-crimper immediately before soybean was sown using a no-tillage technique. Conventional tillage was performed to compare the systems with respect to their weed control efficiency, crop development and soybean yield. The results showed that the no-tillage system had a greater effect on suppressing summer annual weed species (Chenopodium album (L.), Echinochloa crus-galli (L.) P. Beauv. and Amaranthus retroflexus (L.)) than the tillage systems. Conventional tillage and reduced tillage showed increased suppression of the weed species Matricaria inodora (L.), Stellaria media (L.) Vill. and Sonchus arvensis (L.), which were present in the no-tillage system. However, in the conventional tillage and reduced tillage systems, an additional weed control treatment was necessary to suppress the summer annual weeds and ensure high yields. The cover crop rye resulted in weed control similar to that of barley in the no-tillage system. Despite the low weed density, the no-tillage system with a rolled cover crop showed a yield reduced of 47%, whereas the yield of the reduced tillage system was decrease by 23% compared with the conventional tillage system.
Agronomic and technical evaluation of herbicide spot spraying in maize based on high-resolution aerial weed maps - an on-farm trial
(2024) Allmendinger, Alicia; Spaeth, Michael; Saile, Marcus; Peteinatos, Gerassimos G.; Gerhards, Roland; Allmendinger, Alicia; Department of Weed Science, Institute for Phytomedicine, University of Hohenheim, 70599 Stuttgart, Germany; (A.A.);; Spaeth, Michael; Department of Weed Science, Institute for Phytomedicine, University of Hohenheim, 70599 Stuttgart, Germany; (A.A.);; Saile, Marcus; Department of Weed Science, Institute for Phytomedicine, University of Hohenheim, 70599 Stuttgart, Germany; (A.A.);; Peteinatos, Gerassimos G.; ELGO-DIMITRA, Leof Dimokratias 61, Agii Anargiri, 135 61 Athens, Greece;; Gerhards, Roland; Department of Weed Science, Institute for Phytomedicine, University of Hohenheim, 70599 Stuttgart, Germany; (A.A.);; Rossi, Vittorio
Spot spraying can significantly reduce herbicide use while maintaining equal weed control efficacy as a broadcast application of herbicides. Several online spot-spraying systems have been developed, with sensors mounted on the sprayer or by recording the RTK-GNSS position of each crop seed. In this study, spot spraying was realized offline based on georeferenced unmanned aerial vehicle (UAV) images with high spatial resolution. Studies were conducted in four maize fields in Southwestern Germany in 2023. A randomized complete block design was used with seven treatments containing broadcast and spot applications of pre-emergence and post-emergence herbicides. Post-emergence herbicides were applied at 2–4-leaf and at 6–8-leaf stages of maize. Weed and crop density, weed control efficacy (WCE), crop losses, accuracy of weed classification in UAV images, herbicide savings and maize yield were measured and analyzed. On average, 94% of all weed plants were correctly identified in the UAV images with the automatic classifier. Spot-spraying achieved up to 86% WCE, which was equal to the broadcast herbicide treatment. Early spot spraying saved 47% of herbicides compared to the broadcast herbicide application. Maize yields in the spot-spraying plots were equal to the broadcast herbicide application plots. This study demonstrates that spot-spraying based on UAV weed maps is feasible and provides a significant reduction in herbicide use.
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.
Analysis of the emerging situation of resistance to succinate dehydrogenase inhibitors in Pyrenophora teres and Zymoseptoria tritici in Europe
(2018) Rehfus, Alexandra; Vögele, Ralf
Phytopathogenic fungi such as Pyrenophora teres and Zymoseptoria tritici cause destructive diseases of barley and wheat in all major cereal production areas worldwide. The control of net blotch of barley caused by P. teres and Septoria tritici blotch (STB) of wheat caused by Z. tritici mainly relies on the usage of fungicides. Thereby, three single-site inhibiting fungicide classes, the quinone outside inhibitors (QoIs), the demethylation inhibitors (DMIs) and the succinate dehydrogenase inhibitors (SDHIs) have the highest relevance. The class of SDHIs is the most newly introduced fungicide class and inhibits the fungal succinate dehydrogenase complex (SDH) which is a critical enzyme of the respiratory chain and the tricarboxylic cycle. The upcoming SDHI resistance in European populations of P. teres and Z. tritici was investigated in the present study and resistance mechanisms underlying SDHI resistance were characterised. SDHI resistant isolates of both pathogens were collected in intensive monitoring programmes which covered the major barley and wheat growing areas in Europe. SDHI resistant isolates showed point mutations in the genes SdhB, SdhC and SdhD which cause amino acid alteration in the subunits B, C and D of the SDH complex. First SDHI resistant isolates of both pathogens were detected in 2012 and showed amino acid alteration, histidine to tyrosine at position 277 in SDH B (B-H277Y) in the case of P. teres and a threonine to asparagine exchange at position 79 in SDH-C (C-T79N) in the case of Z. tritici. In P. teres, a significant increase of SDHI resistant isolates from 2012 to 2015 was observed, particularly in countries such as France and Germany. Several target-site mutations leading to amino acid exchanges, namely B-H277Y, C-S73P, C-N75S, C-G79R, C-H134R, C-S135R, D-D124N/E, D-H134R, D-G138V, D-D145G and D-E178K, were identified in those isolates. Sequencing of SdhB, SdhC and SdhD genes of several isolates confirmed that each isolate carried one mutation in the Sdh genes, and not two or more in combination. In vitro and in planta sensitivity tests were performed and revealed that each SDH-variant causes a distinct resistance phenotype towards SDHIs. Commercially available SDHIs were compared and isolates showed cross-resistance towards all SDHIs tested, although some minor differences in the response to different mutations were observed. Most of the SDHI resistant P. teres isolates carried C-G79R substitution which was shown to exhibit one of the strongest effects of all detected alterations. In addition to C-G79R, other substitutions, such as C-N75S and D-D145G, were frequently found in the field. These SDH-variants were shown to confer low to moderate levels of resistance. In contrast to the rapid ‘build-up’ of resistant isolates in the population of P. teres in countries such as France and Germany, the emergence of SDHI resistance in Z. tritici did not evolve as fast as observed in net blotch. Here, only a few resistant isolates have been sampled so far (42 resistent of 3431 investigated isolates, 1.2%). An increase of resistant isolates of Z. tritici was observed mainly in Ireland, the United Kingdom and the Netherlands, however, still at low levels. SDH variants B-N225I, B-T268I/A, C-N86S/A, C-T79N/I, C-W80S, C-H152R and C-V166M were detected in SDHI resistant isolates collected in these and other countries such as France and Germany. Four isolates showed two mutations in the Sdh genes in combination. In vitro and in planta sensitivity measurements demonstrated that C-H152R mutants showed the highest resistance level of all investigated SDH variants collected in the field. C-T79N and C-N86S exchanges which have been detected more frequently in the field than C-H152R, were shown to confer lower levels of resistance compared to C-H152R. Both phytopathogenic species were shown to evolve a range of diverse target-site mutations, which led to different alterations in both pathogen species with exception of C-N75S in P. teres and the homologous variant, C-N86S, in Z. tritici. This can be explained by species-specific variation of the SDH enzyme, a different nature of the pathogens (e.g. host plants and disease geographical spread) as well as a different fungicide use pattern (e.g. mode of action diversity and fungicide application intensity). The absence of a dominant major target-site mutation in the case of SDHI resistance in both pathogens is thought to allow SDHIs as effective control agent against both pathogen species also in the future. Nevertheless, anti-resistance management strategies are highly recommended for the usage of SDHIs. These strategies should not only be based on the use of mixtures and alternations of fungicides but should also implement integrated disease control measurements (e.g. resistant host cultivars).
Anthracnose in white lupin : genetic diversity, virulence and host resistance
(2022) Alkemade, Joris A.; Vögele, Ralf
White lupin (Lupinus albus L.) is a grain legume that is known for its high protein content, nutritional quality, efficient nitrogen fixation and unique ability to form specialized cluster roots that support phosphorus uptake. Despite a severe production decline at the end of the past century, white lupin has seen a recent revival to sustain the demand for plant-based protein and reduce Europe’s dependency on imported soybean. A major problem in (white) lupin cultivation is anthracnose disease, caused by the globally dispersed, seed- and air-borne fungal pathogen Colletotrichum lupini. This PhD thesis aims to provide insights on how to sustainably control anthracnose disease in white lupin in order to support its re-introduction into European cultivation systems. It describes (i) the genetic diversity, phylogeography and virulence of C. lupini, (ii) the development of a high-throughput phenotyping protocol to reliably screen white lupin germplasm, (iii) a genome-wide association study identifying resistance candidate genes and (iv) the exploration of effective seed treatments to reduce the primary pathogen inoculum. Multi-locus phylogeny and morphological characterization of 39 C. lupini isolates showed that diversity is greater than previously reported, distinguishing a total of six genetic groups and ten distinct morphotypes. Highest diversity was found across the South American Andes, indicating it to be the center of origin of C. lupini. Results reveal that the current pandemic is caused by strains belonging to genetic group II, which are spread globally, and are genetically and morphologically uniform. Group II isolates were shown to be highly aggressive on tested white and Andean lupin accessions. Isolates belonging to the other five genetic groups were mostly found locally and showed distinct virulence patterns on both white and Andean lupin accessions. Despite its uniformity, it was shown that two highly virulent group II isolates from Chile could overcome resistance of elite white lupin breeding material, stressing the need to implement phytosanitary protocols for international seed transports. A reliable high-throughput phenotyping tool was developed to identify anthracnose resistance in white lupin germplasm and study pathogen-host interactions. Phenotyping under controlled conditions, performing stem wound inoculation on seedlings, showed to be applicable for high-throughput and its disease scores strongly correlated with two-year Swiss field disease assessments (r = 0.95) and yield (r = -0.64). Phenotyping a diverse set of 40 white lupin accessions revealed eight accessions with improved resistance to anthracnose, which can be incorporated into white lupin breeding programs. A genome-wide association study (GWAS) was done to dissect the genetic architecture for anthracnose resistance in white lupin. White lupin genotypes, collected from the center of domestication and traditional cultivation regions, were screened for anthracnose resistance and characterized through genotyping-by-sequencing (GBS). GWAS revealed two significant SNPs associated with anthracnose resistance on gene Lalb_Chr05_g0216161, encoding a RING zinc-finger E3 ubiquitin ligase potentially involved in plant immunity. Further validation experiments are now required to confirm involvement in plant resistance. Population analysis showed a remarkably fast linkage disequilibrium (LD) decay, weak population structure and grouping of commercial varieties with landraces, corresponding to the slow domestication history and scarce breeding efforts in white lupin. A total of eleven different seed treatments was tested in field trials in Switzerland between 2018 and 2021 to identify treatments that reduce C. lupini infection levels in white lupin. Treatments consisted of hot water, steam, electron, long term storage, vinegar, plant extracts and biological control agents (BCAs). The BCAs were tested under controlled conditions for potential antagonistic activity against C. lupini during white lupin infection prior to field trials. Results showed that long term storage and vinegar treatments can successfully reduce disease incidence and increase yield to levels similar to those observed for certified seeds. In order to sustainably and effectively control anthracnose disease in white lupin, an integrative approach, including modern breeding efforts, disease prevention strategies and mixed cropping systems, is recommended. Further research is required to increase our understanding on white lupin-C. lupini interaction and to identify genetic regions involved in resistance or virulence, respectively, which could greatly support white lupin breeding. This thesis provides the basis to further explore C. lupini population dynamics, virulence and host-speciation, white lupin resistance mechanisms and sustainable ways to control anthracnose disease in order to further facilitate successful white lupin cultivation.
Arthropods as vectors of grapevine trunk disease pathogens: Quantification of Phaeomoniella chlamydospora on arthropods and mycobiome analysis of earwig exoskeletons
(2024) Brandenburg, Elisa Maria; Vögele, Ralf; Fischer, Michael; Behrens, Falk Hubertus
Viticulture worldwide is challenged by grapevine trunk diseases (GTDs). Involvement of arthropods in the dissemination process of GTD pathogens, notably esca pathogens, is indicated after detection of associated pathogens on arthropod exoskeletons, and demonstration of transmission under artificial conditions. The present study is the first to quantify spore loads via qPCR of the esca-relevant pathogen Phaeomoniella chlamydospora on arthropods collected in German vineyards, i.e., European earwigs (Forficula auricularia), ants (Formicidae), and two species of jumping spiders (Marpissa muscosa and Synageles venator). Quantification of spore loads showed acquisition on exoskeletons, but most arthropods carried only low amounts. The mycobiome on earwig exoskeletons was described for the first time to reveal involvement of earwigs in the dispersal of GTDs in general. Metabarcoding data support the potential risk of earwigs as vectors for predominantly Pa. chlamydospora and possibly Eutypa lata (causative agent of Eutypa dieback), as respective operational taxonomical unit (OTU) assigned genera had relative abundances of 6.6% and 2.8% in total reads, even though with great variation between samples. Seven further GTD-related genera were present at a very low level. As various factors influence the successful transmission of GTD pathogens, we hypothesize that arthropods might irregularly act as direct vectors. Our results highlight the importance of minimizing and protecting pruning wounds in the field.
Assessment of a postharvest treatment with pyrimethanil via thermo-nebulization in controlling storage rots of apples
(2021) Büchele, Felix; Neuwald, Daniel A.; Scheer, Christian; Wood, Rachael M.; Vögele, Ralf T.; Wünsche, Jens N.
Apples are very susceptible to infections from various fungal pathogens during the growing season due to prolonged exposure to environmental influences in the field. Therefore, a strict and targeted fungicide strategy is essential to protect fruit and trees. Increased environmental and health concerns and pathogen resistance have resulted in a rising demand to reduce fungicide usage and residues on marketed fruit. Thus, producers must develop new plant protection strategies to conform to the legal and social demands while still offering high-quality apples. This study assessed the efficacy of a post-harvest fungicide treatment with pyrimethanil via thermo-nebulization for controlling storage rots and compared the results to those of standard pre-harvest fungicide strategies. The results showed that a single post-harvest application of pyrimethanil successfully controlled storage rots and is comparable to strategies using multiple pre-harvest fungicide applications. The control of fungal rot was sustained even after 5 months of storage and 2 weeks of shelf life. Thermo-nebulization into the storage facility allowed for a lower dosage of fungicide to be used compared to pre-harvest applications, while still maintaining optimal rot control. Residue analyses showed that the post-harvest fungicide treatment did not exceed legal or retailer’s standards.
Bromus-Arten in Winterweizen: Verbreitung, Bedeutung und Populationsdynamik
(2005) Moray, Ralph; Hurle, Karl
The increase of reduced tillage in agriculture and winter cereal dominated crop rotations has lead to a rise of annual and perennial grass weeds in the last decades. One of these are Bromus species that occur worldwide in cereal growing areas. In Germany they also attract more and more interest because of their increasing distribution. Therefore an inves-tigation was conducted to assess the current situation of Bromus species in Germany, competition, population biology and control. Additionally, control strategies were designed on the basis of analyses of population-dynamical parameters. A survey carried out in Germany, showed that Bromus sterilis and B. secalinus were found to be the dominant species. The problems that were predominantly mentioned were yield loss and difficulties at harvest which mostly appear in winter wheat. Their occurrence is closely connected with reduced tillage, early seeding and winter cereal dominated crop rotations whereas Bromus densities can be reduced effectively with a mouldboard plough or the increase of spring crops in crop rotation. In dicot. crops the chemical control was regarded as very good, whereas in cereals between good to sufficient. All of the survey participants expected a further distribution of Bromus species on arable land. Field trials were conducted on three locations over a period of three years to investigate the competition of B. sterilis, B. secalinus, B. tectorum and B. japonicus in winter wheat. Weed density and seeding date of winter wheat were considered for the species competition studies. The trials showed that distinct yield losses could be recorded in winter wheat depending on the different Bromus species. Thresholds where calculated based on the relationship between weed density and yield loss. The thresholds for the Bromus species in winter wheat were below the values given in literature for other grass weeds in winter cereals. This highlights the strong competitiveness of the species. Additionally the results showed that with late seeding the weed density decreases distinctively and thereby the yield loss can be reduced by half. Greenhouse trials on the efficiency of the three in Germany registered herbicides for the control of Bromus species showed, that a sufficient control of B. sterilis and B. secalinus could not always be achieved with the recommended dose. The simulation of the population dynamics showed clearly that with reduced tillage and direct seeding in a winter wheat monoculture without control measures a very fast increase of densities within two growing seasons up to a density-dependent level where high yield losses can be expected. In contrast mouldboard ploughing can control the species to 100 % as a depth of seeds of 10 cm already reduces emergence by half and seeds in the trials showed to have longevity in soil of no longer that 12 months. Moreover, it was demonstrated that the soil cultivation has a higher influence on the development of the weed population than the different seeding dates of winter wheat. The simulation under the influ-ence of herbicide application suggested, that it is possible to practice a winter cereal dominated crop rotation without yield losses. From the results of the investigations it can be concluded that Bromus as a problem in win-ter cereal dominated crop rotation in our latitudes will increase. In fact the control with available herbicides is not always sufficient, but for economical reasons integrated control strategies can not always be considered although quite a good control is given. Therefore one can presume that in future the control of Bromus in winter cereals still will be based on the use of herbicides and that these weed species will be as common in win-ter cereals as it became Alopecurus myosuroides and Apera spica-venti.
Camera-guided weed hoeing in winter cereals with narrow row distance
(2020) Gerhards, Roland; Kollenda, Benjamin; Machleb, Jannis; Möller, Kurt; Butz, Andreas; Reiser, David; Griegentrog, Hans-Werner
Farmers are facing severe problems with weed competition in cereal crops. Grass-weeds and perennial weed species became more abundant in Europe mainly due to high percentages of cereal crops in cropping systems and reduced tillage practices combined with continuous applications of herbicides with the same mode of action. Several weed populations have evolved resistance to herbicides. Precision weed hoeing may help to overcome these problems. So far, weed hoeing in cereals was restricted to cropping practices with row distances of more than 200 mm. Hoeing in cereals with conventional row distances of 125–170 mm requires the development of automatic steering systems. The objective of this project was to develop a new automatic guidance system for inter-row hoeing using camera-based row detection and automatic side-shift control. Six field studies were conducted in winter wheat to investigate accuracy, weed control efficacy and crop yields of this new hoeing technology. A three-meter prototype and a 6-meter segmented hoe were built and tested at three different speeds in 150 mm seeded winter wheat. The maximum lateral offset from the row center was 22.53 mm for the 3 m wide hoe and 18.42 mm for the 6 m wide hoe. Camera-guided hoeing resulted in 72–96% inter-row and 21–91% intra-row weed control efficacy (WCE). Weed control was 7–15% higher at 8 km h−1 compared to 4 km h−1. WCE could be increased by 14–22% when hoeing was combined with weed harrowing. Grain yields after camera-guided hoeing at 8 km h−1 were 15–76% higher than the untreated control plots and amounted the same level as the weed-free herbicide plots. The study characterizes camera-guided hoeing in cereals as a robust and effective method of weed control.
Characterisation of the sensitivity of Zymoseptoria tritici to demethylation inhibitors in Europe
(2021) Huf, Anna; Vögele, Ralf
The fungal pathogen Zymoseptoria tritici (formerly Septoria tritici) causes Septoria tritici blotch (STB), one of the most yield reducing diseases of wheat worldwide. In addition to cultural control measures and the cultivation of wheat varieties with a level of disease resistance, STB control relies heavily on the application of foliar fungicides with different modes of action. The demethylation inhibitors (DMIs) have been one of the most widely applied fungicides for many decades and belong to one of the most important fungicide modes of action in STB management. DMIs inhibit the sterol 14α-demethylase, an essential enzyme in the ergosterol biosynthesis pathway, encoded by the CYP51 gene of fungi. Widespread and intensive use of the DMIs over time has led to a continuous negative shift in the sensitivity of Z. tritici towards DMIs that have been used for a long time. This shift in sensitivity is mainly driven by the accumulation of mutations in the CYP51 gene resulting in the selection of various CYP51 haplotypes. More recently, CYP51 overexpression and an increased efflux activity, based on the overexpression of the MFS1 transporter, have been shown to be additional mechanisms affecting DMI sensitivity of Z. tritici. Inserts in the CYP51 promotor (CYP51p) and MFS1 promotor (MFS1p) were observed to be responsible for CYP51 and MFS1 overexpression. The prevalence and contribution of different DMI resistance mechanisms to a reduced DMI sensitivity of Z. tritici were investigated in isolates from across Europe in 2016 and 2017. The CYP51 gene of all isolates was sequenced and the CYP51p and MFS1p was investigated for inserts in order to determine the character of the CYP51 haplotypes as well as to identify CYP51 overexpression or if an increased efflux activity was occurring in these isolates. Overall, it was shown that the occurrence of CYP51 haplotypes was still the most frequent and important mechanism conferring a reduction in sensitivity to DMIs by Z. tritici in Europe. Nevertheless, an increase in the frequency of isolates exerting CYP51 overexpression and those exhibiting increased efflux activity was observed compared to earlier studies. Glasshouse data demonstrated that DMIs can still contribute to disease control, and in some cases give full control, of STB even if isolates expressed CYP51 overexpression and/or an increased efflux in addition to also carrying moderately or highly adapted CYP51 haplotypes. However, in order to prevent the further increase and spread of further adapted CYP51 haplotypes plus additional resistance mechanisms in the Z. tritici population across Europe, anti-resistance-management strategies should be a high priority in the use of DMIs. In addition, especially integrated disease management strategies, such as the appropriate choice of cultivars, should be applied in order to keep STB disease pressure low and consequently reduce the number of fungicide applications. Moreover, resistance-management strategies may exploit the limited cross-resistance between different DMIs, for example, by the use of mixtures or alternation of different DMI fungicides. However, control strategies should also incorporate the use of fungicides with different MOAs. The aim of all these strategies is to reduce selection of adapted Z. tritici isolates and consequently to prolong the efficacy of DMIs in STB management.
Characterization of mechanisms of resistance to common insecticides in noctuid pest species and resistance risk assessment for the new lepidopteran specific compound flubendiamide
(2009) Konanz, Stefanie; Zebitz, Claus P. W.
Noctuid species, such as the beet armyworm Spodoptera exigua, the cotton bollworm Helicoverpa armigera and the tobacco budworm Heliothis virescens, are well-known pests in many agricultural cropping systems worldwide. The extensive and widespread use of insecticides against these species has led to the development of resistance against almost all commercially used compounds. The focus of this thesis was on the novel lepidopteran specific compound flubendiamde, to get a detailed overview about the efficacy using different kinds of bioassays for a resistance risk assessment. On the other hand, the underlying possible resistance mechanisms of a S. exigua strain from southern Spain was investigated on the toxicological, biochemical, pharmacokinetic and molecular level. The basic of all further experiments was two bioassay techniques, a leaf-disc spray application and an artificial diet bioassay, on 2nd instar larvae. Flubendiamide and 11 competitors with different mode of actions were tested on three susceptible laboratory strains (HELI-AR, HELI-VI, SPOD-EX S) and one field strain from Spain (SPOD-EX E-98). The aim was to get baseline susceptibilities of the three noctuid species and additionally the resistance profile of strain SPOD-EX E-98 against the different insecticides. The results of the two bioassay techniques were comparable with each other, emamectin shown the highest efficacy followed by low EC50-values for flubendiamide, deltamethrin and indoxacarb. The robust artificial diet bioassay was used for a worldwide resistance monitoring for flubendiamide, and resulting in a mean efficacy of 93% in 18 test populations. An interesting cross-resistance pattern against insecticides with different mode of actions demonstrated the S. exigua strain SPOD-EX E-98, and can be called as ?multi-resistant?. High resistance to three classes of insecticides, pyrethroids, benzoylphenyl ureas and carbamates/organophosphates, was detected in this strain, also moderate resistance levels to endosulfan and indoxacarb. The in vivo application study with the synergist PBO (monooxygenase inhibitor) has shown an additionally participation of this enzyme system towards the deltamethrin resistance in this strain. Additionally, PBO and two esterase inhibitors had no effect to the resistance level of triflumuron (benzoylphenyl urea) and so target-site resistance is likely in this case. Using molecular biological methods, a point mutation (kdr) in the voltage-gated sodium channel of the resistant strain SPOD-EX E-98 was detected, this channel is the target of the pyrethroids. This target-site resistance is particularly responsible for the extremely high resistance factor (~900) of the pyrethroid deltamethrin detected in the bioassays. In order to investigate the pharmacokinetic profiles of deltamethrin, triflumuron and flubendiamide in S. exigua larvae radiolabelled compounds were used. No differences in penetration or excretion of the compounds were observed between the two strains. This suggests that physiological changes have not influence as a possible mechanism of deltamethrin and triflumuron resistance. Four biochemical markers, carboxylesterases (CEs), cytochrome P450-dependent monooxygenases (monooxygenases), glutathione S-transferases (GSTs) and acetylcholinesterases (AChEs), were investigated in both S. exigua strains. These enzyme systems are known to be linked with metabolic detoxification/resistance to diverse insecticides. With the exception of GST, in the multi-resistant SPOD-EX E-98 strain was found significantly higher enzyme activities to the other three marker enzymes. The higher CE activity in the multi-resistant strain SPOD-EX E-98 was further investigated, using an nPAGE to obtaining the iso-enzyme banding patterns of both strains. In comparison, the strain SPOD-EX E-98 exhibited an additional thick band and it was not possible to inhibiting this band in vitro through the esterase inhibitor DEF. It is possible that this result is involved in resistance, but only further investigations could be clarify the exact role of the additional band in this resistant strain. The AChE of both S. exigua strains was used for in vitro inhibition studies. The resistant strain SPOD-EX E-98 was insensitive against several organophosphates and carbamates compared with strain SPOD-EX S. Only one exception was detected, the AChE of the resistant strain was more sensible to carbofuran than the enzyme from strain SPOD-EX S. This phenomenon of ?negative cross-insensitivity? is generally correlated with an altered substrate binding site of the AChE. Further investigations of kinetic parameters exhibited a higher turnover of the substrate in strain SPOD-EX E-98. The bioassays confirmed these results and so the resistance mechanism of the two chemical classes is an altered AChE in the resistant strain.
Characterization ofantifungal properties of lipopeptide-producing Bacillus velezensis strains and their proteome-based response to the phytopathogens, Diaporthe spp
(2023) Akintayo, Stephen Olusanmi; Hosseini, Behnoush; Vahidinasab, Maliheh; Messmer, Marc; Pfannstiel, Jens; Bertsche, Ute; Hubel, Philipp; Henkel, Marius; Hausmann, Rudolf; Vögele, Ralf; Lilge, Lars
Introduction: B. velezensis strains are of interest in agricultural applications due to their beneficial interactions with plants, notable through their antimicrobial activity. The biocontrol ability of two new lipopeptides-producing B. velezensis strains ES1-02 and EFSO2-04, against fungal phytopathogens of Diaporthe spp., was evaluated and compared with reference strains QST713 and FZB42. All strains were found to be effective against the plant pathogens, with the new strains showing comparable antifungal activity to QST713 and slightly lower activity than FZB42. Methods: Lipopeptides and their isoforms were identified by high-performance thin-layer chromatography (HPTLC) and mass spectrometric measurements. The associated antifungal influences were determined in direct in vitro antagonistic dual culture assays, and the inhibitory growth effects on Diaporthe spp. as representatives of phytopathogenic fungi were determined. The effects on bacterial physiology of selected B. velezensis strains were analyzed by mass spectrometric proteomic analyses using nano-LC-MS/MS. Results and Discussion: Lipopeptide production analysis revealed that all strains produced surfactin, and one lipopeptide of the iturin family, including bacillomycin L by ES1-02 and EFSO2-04, while QST713 and FZB42 produced iturin A and bacillomycin D, respectively. Fengycin production was however only detected in the reference strains. As a result of co-incubation of strain ES1-02 with the antagonistic phytopathogen D. longicolla, an increase in surfactin production of up to 10-fold was observed, making stress induction due to competitors an attractive strategy for surfactin bioproduction. An associated global proteome analysis showed a more detailed overview about the adaptation and response mechanisms of B. velezensis, including an increased abundance of proteins associated with the biosynthesis of antimicrobial compounds. Furthermore, higher abundance was determined for proteins associated with oxidative, nitrosative, and general stress response. In contrast, proteins involved in phosphate uptake, amino acid transport, and translation were decreased in abundance. Altogether, this study provides new insights into the physiological adaptation of lipopeptide-producing B. velezensis strains, which show the potential for use as biocontrol agents with respect to phytopathogenic fungi.
A comparison of seven innovative robotic weeding systems and reference herbicide strategies in sugar beet (Beta vulgaris subsp. vulgaris L.) and rapeseed (Brassica napus L.)
(2023) Gerhards, Roland; Risser, Peter; Spaeth, Michael; Saile, Marcus; Peteinatos, Gerassimos
More than 40 weeding robots have become commercially available, with most restricted to use in crops or fallow applications. The machines differ in their sensor systems for navigation and weed/crop detection, weeding tools and degree of automation. We tested seven robotic weeding systems in sugar beet and winter oil‐seed rape in 2021 and 2022 at two locations in Southwestern Germany. Weed and crop density and working rate were measured. Robots were evaluated based on weed control efficacy (WCE), crop stand loss (CL), herbicide savings and treatment costs. All robots reduced weed density at least equal to the standard herbicide treatment. Band‐spraying and inter‐row hoeing with RTK‐GPS guidance achieved 75%–83% herbicide savings. When hoeing and band spraying were applied simultaneously in one pass, WCE was much lower (66%) compared to the same treatments in two separate passes with 95% WCE. Hoeing robots Farmdroid‐FD20®, Farming Revolution‐W4® and KULTi‐Select® (+finger weeder) controlled 92%–94% of the weeds. The integration of Amazone spot spraying® into the FD20 inter‐row and intra‐row hoeing system did not further increase WCE. All treatments caused less than 5% CL except for the W4‐robot with 40% CL and the combination of conventional inter‐row hoeing and harrowing (21% CL). KULT‐Vision Control® inter‐row hoeing with the automatic hydraulic side‐shift control resulted in 80% WCE with only 2% CL. Due to the low driving speed of maximum 1 km h−1 of hoeing robots with in‐row elements, treatment costs were high at 555–804 € ha−1 compared to camera‐guided inter‐row hoeing at 221 € ha−1 and broadcast herbicide application at 307–383 € ha−1. Even though the costs of robotic weed management are still high, this study shows that robotic weeding has become a robust, and effective weed control method with great potential to save herbicides in arable and vegetable crops.
Consequences for weed management in crop rotations by introducing imidazolinone-tolerant oilseed rape varieties
(2012) Krato, Christoph; Gerhards, Roland
OSR (Brassica napus L.) is one of the most important arable oil crops globally and is grown on an area of 31,680,945 ha as winter- and spring-sown varieties. The harvest is mainly used in human nutrition, animal feeding and as a renewable resource for the production of paints, varnishes and biodiesel. OSR can be considered a quite competitive crop but nonetheless weed control is carried out on the vast majority of the grown area. The most common treatments are done PRE-E or early POST-E, mainly as prophylactic treatments without exact knowledge of the weed species or their densities. In order to facilitate a more targeted weed control in OSR, IT varieties combined with the corresponding imidazolinone herbicide imazamox (target-site is ALS) + metazachlor/quinmerac (Clearfield® production system) were developed for the European market by BASF SE and several breeding companies. By integrating IT plants into cropping systems, herbicide-tolerance genes will appear in agricultural ecosystems. Unless the tolerance is achieved by non-transgenic breeding methods, the introduction creates concerns regarding spreading the herbicide-tolerance in space and time causing unwanted changes for volunteer OSR management. The aim of the present study was to investigate important aspects, which are likely to arise with a commercial introduction and cultivation of IT OSR in Europe: POST-E weed control was successful using IT varieties. The total herbicide efficacy of imazamox/metazachlor/quinmerac was about 90 % in the field trials. Good results were achieved against volunteer cereals, Thlaspi arvense, Chenopodium album, Matricaria inodora, Papaver rhoeas, Capsella bursa-pastoris and Apera spica-venti but a lack of efficacy was observed regarding control of Agropyron repens and Viola arvensis. Yield was increased significantly in treated plots compared to untreated ones by up to 50 %. IT OSR can be a tool for the use of damage thresholds in integrated weed management in OSR. Outcrossing between IT and IS OSR varieties was confirmed with outcrossing frequencies between 0.57 and 2.05 % between pollen donors and acceptors that were directly adjacent. Outcrossing declined significantly with increasing distance but was still found 45 m from IT plants. The transfer of both tolerance genes and heterozygosity was shown by 84 % of analysed F1-plants. A cross-tolerance of IT OSR to SUs, TPs and SCTs was shown in greenhouse bioassays and field trials with calculated resistance factors between 5 and 775. Furthermore, homozygous IT plants expressed a much higher tolerance level compared to heterozygous ones. Herbicides with alternative modes of action other than HRAC B (ALS-inhibition) were found to be effective to control IT volunteers in subsequent crops. Pendimethalin, picolinafen, isoproturon, diflufenican, florasulam, flufenacet and flurtamone controlled IT volunteers in WW. In sugar beet, herbicide combinations with metamitron, desmedipham, phenmedipham, ethofumesate, chloridazon and lenacil were able to control IT volunteers but single active ingredients were not. Significant negative correlations were detected for the independent variable volunteer OSR density and the wheat yield parameters heads m-2, HW and yield. In contrast, moisture content of wheat and percentage of dockage increased with increasing volunteer density. The highest volunteer density of 261 plants m-2 caused a maximum yield loss of 68 % in WW. Based on a non-linear regression analysis, a single volunteer OSR plant per m2 causes a yield loss of between 0.74 and 1.61 %. In conclusion, the use of IT OSR varieties can substitute the herbicide clomazone in the future and provide POST-E weed control with detailed knowledge of the weed spectrum. This can promote integrated weed management, the use of damage thresholds in weed control and working management benefits for growers. Clearly, difficulties in volunteer management are a drawback of IT OSR, but with conducting an accurate, delayed tillage after OSR harvest and adjusting herbicide regimes in subsequent crops, IT volunteers should not cause more harm compared to IS OSR volunteers. Based on the assumption that innovations in development of new active ingredients for weed control cannot be expected, the use of HT crops has to be seen as a major tool to solve issues in weed management.
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.
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.
Development and testing of new robotic weeding techniques for ridge and flat tillage systems
(2024) Alagbo, Oyebanji Olubunmi; Gerhards, Roland
Under changing climate, conservative tillage practice is expected to gain more popularity over conventional tillage in terms of reduced energy emission and drought resilience. Hence, a need to develop cheap-climate-smart farming solutions for the future. The results of four different studies are summarized below. The first review article summarized different forms of ridge tillage and their impact on crop yield, weed seedbank dynamics, and weed management. Due to improved soil structure and optimal soil moisture conditions provided by ridges, several studies have proven that ridges can accelerate crop emergence, thus stimulating early-stage competitiveness of crops against weeds. More importantly, re-compacted ridges may give more benefits in the long term. The study further emphasized the use of RTK-GNSS (real-time kinematic global satellite navigation systems) ridging system for pilot hoeing, spraying, and seeding – as a cheap alternative to automatic vision control weeding systems in flat seedbeds. In the second article, an autosteered living mulch seeder and hoeing prototypes (using RTK-GNSS-created ridges as a guide) were developed and tested. The impact of ridge re-compaction on soil physical properties was also evaluated. In the two-year field experiment, the combined hoeing and living mulch seeding prototypes attained 70 – 80% weed control efficacy (WCE) with no record of crop losses. This result was comparable to similar treatment in flat seedbeds. Temperature and soil moisture in re-compacted ridges were partly better than in flat seedbeds, whereas, root penetration significantly improved on ridges (40% higher) with relative gain in root biomass (ca. 53.6 g m-2) compared to flat seedbeds. The third study evaluated the performance of different autonomous hoeing combinations on re-compacted ridges. It was hypothesized that autonomous weeding methods using RTK-GNSS-created ridges can substitute broadcast herbicide and manual weeding in future farms. Six field trials were conducted including maize and soybean. The treatment options include; i). twice hoeing combined with band herbicide application on ridge tops, ii). twice hoeing, iii). twice hoeing combined with living mulch, iv). twice hoeing combined with post-emergent harrowing on ridge tops. All hoeing treatments significantly reduced weed density in maize and soybean cultures except for one pass of post-emergent harrowing. In maize and soybean respectively, twice hoeing combined with band herbicide application on ridge tops or twice hoeing combined with living mulch in valleys achieved 70 - 100% and 77 - 86% WCE (within inter-row areas) and 66 - 72% and 67 - 79% WCE (within intra-row areas). Post-emergent harrowing treatments on ridge tops performed poorly in maize (46% WCE) and soybean (10% WCE). Therefore, twice hoeing combined with band herbicide application on ridge tops or twice hoeing combined with living mulch in the valley were considered best in selectivity due to higher weed control efficacy (inter – and intra-row), little or no crop damage, and highest grain yield as comparable to broadcast herbicide applications. The fourth article evaluated four autonomous inter and intra-row weeding methods in maize, sunflower, and sugar beet. Within the intra-row area, the treatment involved are; finger weeding, AI-based hoeing actuators, and band herbicide spraying – each simultaneously combined with sensor-guided inter-row hoeing using K.U.L.T iSelect®. In the six experiments conducted, all treatments attained higher yield, with more than 77% reduction in weed density. Most experiments recorded non-significant crop losses. Intra-row band-spraying or AI-based hoeing actuation (combined with inter-row hoeing) achieved 91% and 77% WCE respectively across maize, sugar-beet, and sunflower. However, as an autonomous system, band herbicide treatment was preferable in terms of herbicide savings (60%) and tractor speed comparable to broadcast herbicide application.
Development of a sensor-based harrowing system using digital image analysis to achieve a uniform weed control selectivity in cereals
(2021) Spaeth, Michael; Gerhards, Roland
Using intelligent sensor technology for site-specific weed control can increase the efficacy of traditional weed control implements. Several scientific studies successfully used intelligent sensors for automatic harrow control by taking many different parameters into account such as weed density, soil resistance factor, and plant growth. However, none of the systems was practically feasible because these factors made the control system too complex and unattractive for farmers. Defining only one parameter (crop soil cover) instead of many provides a new and simple approach which was investigated in this work. The first scientific publication focuses on the development, practical implementation and testing of the automatic harrow control system. Two RGB-cameras were mounted before and after the harrow and constantly monitored crop cover. The CSC was then computed out of these resulting images. The image analysis, decision support system and automatic control of harrowing intensity by hydraulic adjustment of the tine angle were installed on a controller which was mounted on the harrow. Eight field experiments were carried out in spring cereals. Mode of harrowing intensity was changed in four experiments by speed, number of passes and tine angle. Each mode was varied in five intensities. In four experiments, only the intensity of harrowing was changed. Modes of intensity were not significantly different among each other. However, intensity had significant effects on WCE and CSC. Cereal plants recovered well from 10% CSC, and selectivity was in the constant range at 10% CSC. Therefore, 10% CSC was the threshold for the decision algorithm. If the actual CSC was below 10% CSC, intensity was increased. If the actual CSC was higher than 10%, intensity was decreased. The new system was tested in an additional field study. Threshold values for CSC were set at 10%, 30% and 60%. Automatic tine angle adjustment precisely realised the three different CSC values with variations of 1.5% to 3%. The next publication discussed and assessed the site-specific field adaptation of the development in cereals. In 2020, three field experiments were conducted in winter wheat and spring oats to investigate the response of the weed control efficacy and the crop to different harrowing intensities, in southwest Germany. In all experiments, six levels of CSC were tested. Each experiment contained an untreated control and an herbicide treatment as a comparison to the harrowing treatments. The results showed an increase in the WCE with an increasing CSC threshold. Difficult-to-control weed species such as Cirsium arvense (L.) and Galium aparine (L.) were best controlled with a CSC threshold of 70%. With a CSC threshold of 20% it was possible to control up to 98% of Thlaspi arvense (L.) The highest crop biomass, grain yield, and selectivity were achieved with an CSC threshold of 20–25% at all trial locations. With this harrowing intensity, grain yields were higher than in the herbicide control plots and a WCE of 68–98% was achieved. The last scientific article compares pairwise a conventional harrow intensity with automatic sensor-based harrowing intensity. Five field experiments in cereals were conducted at three locations in southwestern Germany in 2019 and 2020 to investigate if camera-based harrowing resulted in a more homogenous CSC and higher WCE, biomass, and crop grain yield than a conventional harrow with a constant intensity across the whole plot. For this purpose, pairwise comparisons of three fixed harrowing intensities (10 °, 40 °, and 70 ° tine angle) and three predefined CSC thresholds (CSC of 10%, 20%, and 60%) were realized in randomized complete block designs. Camera-based adjustment of the intensity resulted in 6-16% less standard deviation variation of CSC compared to fixed settings of tine angle. Crop density, WCE, crop biomass and grain yield were significantly higher for camera-based harrowing than for conventional harrowing. WCE and yields of all automatic adjusted harrowing treatments were equal to the herbicide control plots. In this PhD-thesis, a sensor-based harrow was developed and successfully investigated as an alternative to conventional herbicide application in cereals. A permanent, equal replacement of chemical weed control in arable farming systems can only be achieved using modern, sensor-based mechanical weed control approaches. Therefore, the efficacy of the mechanical weed control method can be improved and increased continuously. It has been shown that the precise adjustment of mechanical weed control methods to site-specific weed conditions allows similar WCE results as an herbicide application without causing yield losses. These findings contribute towards modern plant protection strategies to reduce the herbicide use and to establish the acceptance of technical progress in society.
Development of a spatial data infrastructure for precision agriculture applications
(2021) Jackenkroll, Markus; Gerhards, Roland
Precision agriculture (PA) is the technical answer to tackling heterogeneous conditions in a field. It works through site specific operations on a small scale and is driven by data. The objective is an optimized agricultural field application that is adaptable to local needs. The needs differ within a task by spatial conditions. A field, as a homogenous-planted unit, exceeds by its size the scale units of different landscape ecological properties, like soil type, slope, moisture content, solar radiation etc. Various PA-sensors sample data of the heterogeneous conditions in a field. PA-software and Farm Management Information Systems (FMIS) transfer the data into status information or application instructions, which are optimized for the local conditions. The starting point of the research was the determination that the process of PA was only being used in individual environments without exchange between different users and to other domains. Data have been sampled regarding specific operations, but the model of PA suffers from these closed data streams and software products. Initial sensors, data processing and controlled implementations were constructed and sold as monolithic application. An exchange of hard- or software as well as of data was not planned. The design was focused on functionality in a fixed surrounding and conceived as being a unit. This has been identified as a disadvantage for ongoing developments and the creation of added value. Influences from the outside that may be innovative or even inspired cannot be considered. To make this possible, the underlying infrastructure must be flexible and optimized for the exchange of data. This thesis explores the necessary data handling, in terms of integrating knowledge of other domains with a focus on the geo-spatial data processing. As PA is largely dependent on geographical data, this work develops spatial data infrastructure (SDI) components and is based on the methods and tools of geo-informatics. An SDI provides concepts for the organization of geospatial components. It consists of spatial- and metadata in geospatial workflows. The SDI in the center of these workflows is implemented by technologies, policies, arrangements, and interfaces to make the data accessible for various users. Data exchange is the major aim of the concept. As previously stated, data exchange is necessary for PA operations, and it can benefit from defined components of an SDI. Furthermore, PA-processes gain access to interchange with other domains. The import of additional, external data is a benefit. Simultaneously, an export interface for agricultural data offers new possibilities. Coordinated communication ensures understanding for each participant. From the technological point of view, standardized interfaces are best practice. This work demonstrates the benefit of a standardized data exchange for PA, by using the standards of the Open Geospatial Consortium (OGC). The OGC develops and publishes a wide range of relevant standards, which are widely adopted in geospatially enabled software. They are practically proven in other domains and were implemented partially in FMIS in the recent years. Depending on their focus, they could support software solutions by incorporating additional information for humans or machines into additional logics and algorithms. This work demonstrates the benefits of standardized data exchange for PA, especially by the standards of the OGC. The process of research follows five objectives: (i) to increase the usability of PA-tools in order to open the technology for a wider group of users, (ii) to include external data and services seamlessly through standardized interfaces to PA-applications, (iii) to support exchange with other domains concerning data and technology, (iv) to create a modern PA-software architecture, which allows new players and known brands to support processes in PA and to develop new business segments, (v) to use IT-technologies as a driver for agriculture and to contribute to the digitalization of agriculture.
Development of alternative strategies for the control of the important phytopathogens Phytophthora infestans (Mont.) and Erwinia amylovora (Burrill)
(2007) Swaidat, Ihsan; Buchenauer, Heinrich
Within the framework of two projects, financed by DBU (Deutsche Bundesstiftung Umwelt) and ProInno ("Förderung der Erhöhung der Innovationskompetenz mittelständischer Unternehmen"), respectively, in co-operation with an industrial partner, alternative phytosanitary compounds from natural sources have been screened. High throughput screening systems were developed and used for testing of large numbers of extracts of Actinomycetes in 96-well multiplates against Phytophthora infestans and Erwinia amylovora, the causal agents of tomato late blight and apple fire blight, respectively. These important phytopathogens were chosen as models. According to the Pflanzenschutzgesetz (PflSchG) §2 Nr. 10a, plant strengthening compounds (Pflanzenstärkungsmittel) should not act directly against the pathogen, but via an induction of plant resistance mechanisms. Therefore, one of the projects (DBU) aimed to exclude direct action on P. infestans. Based on the GFP-fluorescence of the P. infestans transformant 208m2, a fluorescence optical measurement of mycelium growth respectively growth inhibition was developed, to test the influence of the extracts and extract fractions. Only 52 out of 8335 extracts significantly inhibited the mycelium growth (Pi+) in this test, and thus had to be excluded according to §2 Nr.10a PflSchG for a potential commercial application. Searching for resistance inducing activity, all extracts were re-tested in parsley cell culture as a model for putative resistance induction characterised by formation of furanocoumarin phytoalexins. Only 42 out of the whole set of extracts tested, induced furanocoumarins (Pc+) significantly. In order to test if the induction correlates with a successful defence of host tissue against P. infestans, detached tomato leaves were treated with these Pc+ extracts. Only one extract resulted in formation of small sharp necrosis symptoms after pathogen inoculation, leading to strongly reduced infection and inhibited sporulation. The identification of the active ingredient is currently performed. When comparing the 52 direct acting substances (Pi+) with the potentially resistance inducing compounds (Pc+), three were also found actively inhibiting P. infestans in the host tissue. These three extracts also induced limited dark brown necrosis, suggesting an induction of hypersensitive reaction (HR). Infection area and sporulation level were reduced to levels below 25% of total leaf area. Microscopic investigations showed non-germinated or abnormally shaped germinated sporangia. Promising extracts were fractionated by the cooperation partner. Fraction 1 of one Pi+-extract (014 008-2) reduced the sporulation level and the size of the infection area to 5 and 25%, respectively, compared to the control. Application of fraction 2, although less effective than fraction 1, produced sporangiophores that were morphologically abnormal carrying no sporangia, indicating a possible highly specific action on a certain developmental step of the pathogen. In case of the extracts tested in vitro against E. amylovora, only 60 out of 5236 extracts inhibited bacterial growth. Only extracts showing a similar effect as the streptomycin positive control (12 extracts), were also tested in the cell culture of parsley for a potential resistance induction. The effect of such promising extract (000 391 CF) was compared in in vitro apple plantlets with two purified substances identified in the in vitro growth inhibition screening (tubercidin and streptothricin) and two commercially available resistance inducers (Prohexadion-Calcium, Bion®) in addition to streptomycin as control. Streptothricin was found nearly as effective as the streptomycin control (2 and 0% diseased shoots, respectively). 000 391 CF with chuanghsinmycin as active ingredient in unknown concentration, however, was less effective together with tubercidin; both compounds were originally classified effective in the in vitro screening (approximately 20 and 30%, respectively). The resistance inducers showed a maximal effectiveness of 20-25% approximately; however, in the highest concentration applied, they caused phytotoxic effects. As an alternative strategy of plant defence, an experiment was performed to silence the GFP-fluorescence of transformant 208m2 as a model for silencing fungal genes responsible for plant infection via the transgenic host. Two types of ?T0? transgenic tomato plants were produced from ?Hellfrucht? cultivar, one carrying the gfp-gene and the other carrying inverted repeat fragment of the gfp-gene (gpg). GFP-expressing plants could be identified by their green fluorescence under UV-A light. gpg-transformants were verified by PCR analysis of their genomic DNA and the formation of siRNAs by Northern blotting. In order to test the silencing effects in the plants Agrobacteria harbouring the gfp-gene or gpg-construct in a binary vector were infiltrated into tomato leaves. Leaves of agro-infiltrated (gfp) wild type plants were found to fluoresce, but no green fluorescence appeared when gpg-tomato leaves were infiltrated, due to the production of siRNAs resulting in gene silencing. The green fluorescence of gfp-tomato leaves disappeared gradually starting from the major vein expanding to small veins after infiltration of gpg-Agrobacteria due to the same phenomenon. However, no systemic silencing over the whole plant was observed; this may be due to the comparatively low expression of the gfp-gene in the?T0? plants used. However, the GFP in the P. infestans transformant 208m2 was not found to be silenced when leaves of gpg-plants were infected; this might be due to unsuccessful passing of siRNAs through haustorium?s membrane system, or due to the comparatively low amount of siRNAs in the gpg-tomato tissues.

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