Oilseed Rape Crops Research Articles

Combination of the degrading bacterium Bacillus cereus MZ-1 and corn straw biochar enhanced the removal of imazethapyr from water solutions

Long residual herbicide imazethapyr has caused a serious threat to subsequent sensitive crop plants and ecological security. Efficient immobilized microorganism technology offers a sustainable solution for remediating pesticides contamination. In this study, three corn straw biochars produced at 300℃, 500℃, and 700℃ were used as carriers to immobilize the imazethapyr degrading strain Bacillus cereus MZ-1, aiming to efficiently remove imazethapyr from the water environment. Response surface methodology was employed to optimize the best immobilization conditions based on the efficiency of imazethapyr removal. The results indicate that the biochar produced at 500 ℃ was the most effective carrier for immobilization, despite having a lower imazethapyr removal capacity compared to the biochar produced at 700 ℃. Additionally, the optimal strain addition amount was a suspension of strain MZ-1 (OD600=1) in a 3.5-fold biochar solution, and the best immobilized time was 18 h. The prepared immobilized MZ-1 achieved a maximum imazethapyr removal efficiency of 79.85 %. Moreover, the immobilized MZ-1 demonstrated enhanced detoxification efficacy against imazethapyr-induced harm in sensitive oilseed rape crops, surpassing the effects of using MZ-1 or biochar alone. Results of this work suggests biochar immobilized degradation strain MZ-1 is a highly effective in-situ remediation strategy for bioremediation of imazethapyr contamination.

Image Segmentation-Based Oilseed Rape Row Detection for Infield Navigation of Agri-Robot

The segmentation and extraction of oilseed rape crop rows are crucial steps in visual navigation line extraction. Agricultural autonomous navigation robots face challenges in path recognition in field environments due to factors such as complex crop backgrounds and varying light intensities, resulting in poor segmentation and slow detection of navigation lines in oilseed rape crops. Therefore, this paper proposes VC-UNet, a lightweight semantic segmentation model that enhances the U-Net model. Specifically, VGG16 replaces the original backbone feature extraction network of U-Net, Convolutional Block Attention Module (CBAM) are integrated at the upsampling stage to enhance focus on segmentation targets. Furthermore, channel pruning of network convolution layers is employed to optimize and accelerate the model. The crop row trapezoidal ROI regions are delineated using end-to-end vertical projection methods with serialized region thresholds. Then, the centerline of oilseed rape crop rows is fitted using the least squares method. Experimental results demonstrate an average accuracy of 94.11% for the model and an image processing speed of 24.47 fps/s. After transfer learning for soybean and maize crop rows, the average accuracy reaches 91.57%, indicating strong model robustness. The average yaw angle deviation of navigation line extraction is 3.76°, with a pixel average offset of 6.13 pixels. Single image transmission time is 0.009 s, ensuring real-time detection of navigation lines. This study provides upper-level technical support for the deployment of agricultural robots in field trials.

Temperature and time of season are the predominant drivers of cabbage stem flea beetle, Psylliodes chrysocephala, arrival at oilseed rape crops

Cabbage stem flea beetle (CSFB) is an economically important pest of oilseed rape crops responsible for substantial yield losses in recent years, particularly since the restrictions on neonicotinoid seed treatment use came into force in 2013. To effectively time sowing dates and target control measures, it is crucial that accurate estimates of when migratory adult CSFB will arrive at the crop can be made. A Bayesian hierarchical model was fitted to data from 19 sites containing adult CSFB traps over a period of three years to characterise the relationship between the day of year, temperature, rainfall, wind speed and solar radiation on beetle counts and to understand their relative importance. Day of the year was identified as the main driver of migration and temperature was the predominant environmental driver of CSFB migration. A hot day (based on the range of observed temperatures over the trapping window) resulted in approximately 300% of the expected CSFB migration relative to an average day during peak migration. The second most important environmental driver of migration was wind speed, but this resulted in a relatively negligible increase of approximately 15% from an average day to a still day. These findings suggest that efforts to predict timing of adult CSFB migration should focus on understanding how the phenology of CSFB and temperature interact to drive the timing of migration.

Tillage Practices Effect on Root Distribution and Variation of Soil CO2 Emission under Different Cropping Strategies

Conservation soil management strategies, particularly no-tillage and cropping strategies, have become an effective and widely adopted practice that has a direct influence on root parameters and mitigation of greenhouse gasses. However, the effect of different tillage and cropping strategies on root growth in field conditions is rarely studied. The study aimed to quantify and characterise the relationship between root network development and CO2 emission and how these parameters are affected by different cropping and tillage strategies. Five different crop rotations were tested, with or without the inclusion of catch crops (CC), by growing them in the soil where different tillage practices were applied. Selected cropping strategies differed among themselves in terms of the frequency of CC grown per rotation. The data revealed that in NT treatments, the CO2 emission (both autotrophic and heterotrophic simultaneously) was 25% higher than in CT. The cropping strategies were identified as an important factor influencing CO2 emissions. An increase in CO2 emission varied between 30 and 35% depending on the share of legume and CC inclusion. The frequency of CC grown per rotation has had an effect on the rate of CO2 emission. The cropping strategy when CC was grown every year showed the lowest amount of CO2 (by 26%), while in other cropping strategies, when CC was grown once or twice per rotation, significantly higher CO2 emissions were observed. Root growth and their development were significantly affected (p < 0.05) by soil depth and cropping strategies concerning root length and root volume changes. The inclusion of CC into the rotations led towards a decrease in root volume (by 21%). Root length (R2 = 0.45; p < 0.05) and root volume (R2 = 0.82; p < 0.05) had a significant impact on soil CO2 emissions. The results collected from 2021 to 2023 experiments indicated that cropping strategies and CC management areas are important tools not only for the improvement of root parameters but also for understanding how they affect CO2 emissions. The main message for stakeholders is that the cropping strategies diversification with the inclusion of CC every year in a winter oil-seed rape, spring wheat and pea crop rotation (R/W/P + CC) had demonstrated the possibilities to reduce CO2 emission and improve the root network parameters as compared to the monoculture strategy.

The Influence of Nitrogen and Sulfur Fertilization on Oil Quality and Seed Meal in Different Genotypes of Winter Oilseed Rape (Brassica napus L.)

Adequate nitrogen (N) and sulfur (S) fertilization of oilseed rape crops is necessary to obtain good-quality oil and post-extraction rapeseed meal. The aim of this study was to determine the effect of different doses of N fertilization (100, 160 and 220 kg ha−1) and S (0, 30, 60 and 90 kg ha−1) on the value of seeds of three winter oilseed rape genotypes. Two winter oilseed rape genotypes obtained by mutagenesis (cultivar Polka and breeding genotype PN440) were characterized by changed fatty acid profile. The cultivar Polka, type HO (high oleic), had a high content of oleic acid (C18:1, 78.0%) and the breeding genotype PN440, type HOLL (high-oleic and low-linolenic), had a high content of oleic acid (C18:1, 75.0%) and a low content of linolenic acid (C18:3, 3.0%). We also used the canola type of winter oilseed rape cultivar, Monolit. The analysed winter oilseed rape genotypes responded similarly to the N and S fertilization factors with regard to the content of crude fat and total protein in the seeds and the composition of fatty acids in the oil. N fertilization increased the content of glucosinolates (GLS-alkenyl, indole and total) in seeds, whereas S application decreased the content of saturated fatty acids (stearic acid-C18:0) in oil and increased the content of alkenyl and total glucosinolates (GLSs) in seeds. A significant interaction between N and S was observed for crude-fat and total-protein content. This study suggests that ensuring an adequate supply of both nitrogen and sulfur in the soil is essential for optimizing meal and oil quality in different types of winter oilseed rape cultivars. Proper management of these nutrients can lead to improved oil content and overall crop performance.

Phytochemical drivers of insect herbivory: a functional toolbox to support agroecological diversification.

Plant metabolism is a key feature of biodiversity that remains underexploited in functional frameworks used in agroecology. Here, we study how phytochemical diversity considered at three organizational levels can promote pest control. In a factorial field experiment, we manipulated plant diversity in three monocultures and three mixed crops of oilseed rape to explore how intra- and interspecific phytochemical diversity affects pest infestation. We combined recent progress in metabolomics with classic metrics used in ecology to test a box of hypotheses grounded in plant defence theory. According to the hypothesis of 'phytochemically mediated coevolution', our study stresses the relationships between herbivore infestation and particular classes of specialized metabolites like glucosinolates. Among 178 significant relationships between metabolites and herbivory rates, only 20% were negative. At the plant level, phytochemical abundance and richness had poor predictive power on pest regulation. This challenges the hypothesis of 'synergistic effects'. At the crop cover level, in line with the hypothesis of 'associational resistance', the phytochemical dissimilarity between neighbouring plants limited pest infestation. We discuss the intricate links between associational resistance and bottom-up pest control. Bridging different levels of organization in agroecosystems helps to dissect the multi-scale relationships between phytochemistry and insect herbivory.

Novel indices reveal that pollinator exposure to pesticides varies across biological compartments and crop surroundings

Declines in insect pollinators have been linked to a range of causative factors such as disease, loss of habitats, the quality and availability of food, and exposure to pesticides. Here, we analysed an extensive dataset generated from pesticide screening of foraging insects, pollen-nectar stores/beebread, pollen and ingested nectar across three species of bees collected at 128 European sites set in two types of crop. In this paper, we aimed to (i) derive a new index to summarise key aspects of complex pesticide exposure data and (ii) understand the links between pesticide exposures depicted by the different matrices, bee species and apple orchards versus oilseed rape crops. We found that summary indices were highly correlated with the number of pesticides detected in the related matrix but not with which pesticides were present. Matrices collected from apple orchards generally contained a higher number of pesticides (7.6 pesticides per site) than matrices from sites collected from oilseed rape crops (3.5 pesticides), with fungicides being highly represented in apple crops. A greater number of pesticides were found in pollen-nectar stores/beebread and pollen matrices compared with nectar and bee body matrices. Our results show that for a complete assessment of pollinator pesticide exposure, it is necessary to consider several different exposure routes and multiple species of bees across different agricultural systems.

Design and Synthesis of Novel Diphenyl Ether Carboxamide Derivatives To Control the Phytopathogenic Fungus Sclerotinia sclerotiorum.

Sclerotinia stem rot (SSR) caused by the phytopathogenic fungus Sclerotinia sclerotiorum has led to serious losses in the yields of oilseed rape and other crops every year. Here, we designed and synthesized a series of carboxamide derivatives containing a diphenyl ether skeleton by adopting the scaffold splicing strategy. From the results of the mycelium growth inhibition experiment, inhibition rates of compounds 4j and 4i showed more than 80% to control S. sclerotiorum at a dose of 50 μg/mL, which is close to that of the positive control (flubeneteram, 95%). Then, the results of a structure-activity relationship study showed that the benzyl scaffold was very important for antifungal activity and that introducing a halogen atom on the benzyl ring would improve antifungal activity. Furthermore, the results of an in vitro activity test suggested that these novel compounds can inhibit the activity of succinate dehydrogenase (SDH), and the binding mode of 4j with SDH was basically similar to that of the flutolanil derivative. Morphological observation of mycelium revealed that compound 4j could cause a damage on the mycelial morphology and cell structure of S. sclerotiorum, resulting in inhibition of the growth of mycelia. Furthermore, in vivo antifungal activity assessment of 4j displayed a good control of S. sclerotiorum (>97%) with a result similar to that of the positive control at a concentration of 200 mg/L. Thus, the diphenyl ether carboxamide skeleton is a new starting point for the discovery of new SDH inhibitors and is worthy of further development.

The INRAE Biological Resource Center ‘BrACySol’: a French centre of valuable genetic resources to address major issues faced by potato and oilseed rape crops

The INRAE Biological Resource Center ‘BrACySol’: a French centre of valuable genetic resources to address major issues faced by potato and oilseed rape crops

Use of an unmanned aerial vehicle for monitoring and prediction of oilseed rape crop performance.

The flowering stage of oilseed rape (Brassica napus L.) is of vital interest in precision agriculture. It has been shown that data describing the flower production of oilseed rape (OSR), at stage 3, in spring can be used to predict seed yield at harvest. Traditional field-based techniques for assessing OSR flowers are based on a visual assessment which is subjective and time consuming. However, a high throughput phenotyping technique, using an unmanned aerial vehicle (UAV) with multispectral image (MSI) camera, was used to investigate the growth stages of OSR (in terms of crop height) and to quantify its flower production. A simplified approach using a normalised difference yellowness index (NDYI) was coupled with an iso-cluster classification method to quantify the number of OSR flower pixels and incorporate the data into an OSR seed yield estimation. The estimated OSR seed yield showed strong correlation with the actual OSR seed yield (R2 = 0.86), as determined using in-situ sensors mounted on the combine harvester. Also, using our approach allowed the variation in crop height to be assessed across all growing stages; the maximum crop height of 1.35 m OSR was observed at the flowering stage. This methodology is proposed for effectively predicting seed yield 3 months prior to harvesting.

The Brassica napus boron deficient inflorescence transcriptome resembles a wounding and infection response.

Oilseed rape and other crops of Brassica napus have a high demand for boron (B). Boron deficiencies result in the inhibition of root growth, and eventually premature flower abortion. Understanding the genetic mechanisms underlying flower abortion in B-limiting conditions could provide the basis to enhance B-efficiency and prevent B-deficiency-related yield losses. In this study, we assessed transcriptomic responses to B-deficiency in diverse inflorescence tissues at multiple time points of soil-grown plants that were phenotypically unaffected by B-deficiency until early flowering. Whilst transcript levels of known B transporters were higher in B-deficient samples, these remained remarkably stable as the duration of B-deficiency increased. Meanwhile, GO-term enrichment analysis indicated a growing response resembling that of a pathogen or pest attack, escalating to a huge transcriptome response in shoot heads at mid-flowering. Grouping differentially expressed genes within this tissue into MapMan functional bins indicated enrichment of genes related to wounding, jasmonic acid and WRKY transcription factors. Individual candidate genes for controlling the "flowering-without-seed-setting" phenotype from within MapMan biotic stress bins include those of the metacaspase family, which have been implicated in orchestrating programmed cell death. Overall temporal expression patterns observed here imply a dynamic response to B-deficiency, first increasing expression of B transporters before recruiting various biotic stress-related pathways to coordinate targeted cell death, likely in response to as yet unidentified B-deficiency induced damage-associated molecular patterns (DAMPs). This response indicates new pathways to target and dissect to control B-deficiency-induced flower abortion and to develop more B-efficient crops.

The structure of plant–pollinator networks is affected by crop type in a highly intensive agricultural landscape

In agricultural landscapes, bipartite networks formed by pollinators and the flowers they forage on, are characterised by the presence of honeybees (Apis mellifera) or crop plants. These managed species can affect the structural properties of these networks because of spatial and temporal variation in the availability of resources, and competition for these resources; for example, crop plants such as oilseed rape and sunflower produce a large number of flowers during a short blooming period. Here, we examined the structure of plant–pollinator networks in an intensive agricultural landscape, the Zone Atelier Plaine & Val de Sèvre (West of France). We compiled a six-year monitoring dataset of plant–pollinator interactions, sampling by sweep-nets along transects in the main six crop types (811 fields in total). To describe networks, we computed six metrics: connectance, nodes number, modularity, specialisation and a nestedness measure. We found that the degree distribution (number of partners per species in the network) fitted better to Fisher’s log-series rather than Power law. Strong differences between crops were observed in nestedness and specialisation, even when accounting for the effect of sample size: in oilseed rape, networks were much more nested and much less specialised than in sunflower. In addition, the link ‘honeybee–crop flower’ differed between the two mass-flowering crops. Honeybees and sunflowers appeared as specialist species in sunflower crops, interacting strongly and almost exclusively with each other, whereas they are usually considered highly generalist species. Indeed, sunflower pollination may be almost entirely driven by honeybees, conversely to oilseed rape crops, where the presence of wild bees and other insects tended to produce a more diversified network.

Assessing the potential of biopesticides to control the cabbage stem flea beetle Psylliodes chrysocephala.

Cabbage stem flea beetle (CSFB) is an economically important pest of oilseed rape crops in Europe that was effectively controlled by neonicotinoid insecticide seed treatments until they were banned by the European Union in 2013. Since then, CSFB has been a difficult pest to control effectively, in part due to many populations having developed resistance to pyrethroids, the only authorized insecticides used to control this pest in many countries. Alternative solutions are therefore necessary, such as biopesticides. We tested an entomopathogenic fungus, three entomopathogenic bacteria isolates, two fatty acids and azadirachtin against CSFB adults under laboratory conditions. We also tested the efficacy of the pyrethroid insecticide lambda-cyhalothrin. Fatty acids were effective, with up to 100% CSFB mortality after 24 h. The entomopathogenic fungus Beauveria bassiana resulted in up to 56% mortality 14 days after treatment. Entomopathogenic bacteria formulations and azadirachtin were not effective (<50% and <40% mortality, respectively). Results from a bioassay using lambda-cyhalothrin indicated that the CSFB used in this study were resistant to this insecticide. Entomopathogenic fungi and fatty acids could potentially be used to control CSFB as part of an integrated pest management programme. This study is the first to investigate the efficacy of different biopesticides to control CSFB under laboratory conditions. As such, these biopesticides require further testing to optimise the formulation and application methods, and to assess the impact on nontarget organisms. Finally, efficacy under field conditions must be determined to understand the influence of environmental variables. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Prediction of Seedling Oilseed Rape Crop Phenotype by Drone-Derived Multimodal Data

In recent years, unmanned aerial vehicle (UAV) remote sensing systems have advanced rapidly, enabling the effective assessment of crop growth through the processing and integration of multimodal data from diverse sensors mounted on UAVs. UAV-derived multimodal data encompass both multi-source remote sensing data and multi-source non-remote sensing data. This study employs Image Guided Filtering Fusion (GFF) to obtain high-resolution multispectral images (HR-MSs) and selects three vegetation indices (VIs) based on correlation analysis and feature reduction in HR-MS for multi-source sensing data. As a supplement to remote sensing data, multi-source non-remote sensing data incorporate two meteorological conditions: temperature and precipitation. This research aims to establish remote sensing quantitative monitoring models for four crucial growth-physiological indicators during rapeseed (Brassica napus L.) seedling stages, namely, leaf area index (LAI), above ground biomass (AGB), leaf nitrogen content (LNC), and chlorophyll content (SPAD). To validate the monitoring effectiveness of multimodal data, the study constructs four model frameworks based on multimodal data input and employs Support Vector Regression (SVR), Partial Least Squares (PLS), Backpropagation Neural Network (BPNN), and Nonlinear Model Regression (NMR) machine learning models to create winter rapeseed quantitative monitoring models. The findings reveal that the model framework, which integrates multi-source remote sensing data and non-remote sensing data, exhibits the highest average precision (R2 = 0.7454), which is 28%, 14.6%, and 3.7% higher than that of the other three model frameworks, enhancing the model’s robustness by incorporating meteorological data. Furthermore, SVR consistently performs well across various multimodal model frameworks, effectively evaluating the vigor of rapeseed seedlings and providing a valuable reference for rapid, non-destructive monitoring of winter rapeseed.

Companion plants and straw mulch reduce cabbage stem flea beetle (Psylliodes chrysocephala) damage on oilseed rape.

Plant diversification, especially sowing crops with the addition of companion plants has been demonstrated as a suitable practice to increase insect pest control in multiple cropping systems. Since the ban on use of neonicotinoid seed treatments in oilseed rape (OSR), the harvested area has reduced significantly in Europe, mainly because of the damage caused by cabbage stem flea beetle (Psylliodes chrysocephala). Several companion plants such as legumes and other species of Brassicaceae have been reported as potential companions for OSR but robust evaluation of their efficiency to reduce cabbage stem flea beetle damage in replicated trials is lacking. Four field trials were conducted in the UK and Germany to test the effect of different companion plants, or the addition of straw mulch, on cabbage stem flea beetle adult feeding and larval infestation in OSR. We found significant differences in the level of feeding damage between treatments in all experiments. Combinations of OSR with cereal companion plants or with straw mulch showed the strongest reduction in adult feeding damage. A protective effect of legumes was also observed in one trial. Differences in larval infestation were also observed between treatments but were not consistent and might be more related to the OSR plant biomass than to treatments. This study shows that companion planting can protect OSR crops from cabbage stem flea beetle adult feeding damage. We show for the first time that not only legumes, but also cereals and the application of straw mulch can have a strong protective effect on the crop. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Dynamics of pollen beetle (Brassicogethes aeneus) immigration and colonization of oilseed rape (Brassica napus) in Europe.

Understanding the dynamics of pest immigration into an agroecosystem enables effective and timely management strategies. The pollen beetle (Brassicogethes aeneus) is a primary pest of the inflorescence stages of oilseed rape (Brassica napus). This study investigated the spatial and temporal dynamics of pollen beetle immigration into oilseed rape fields in Denmark and the UK using multiple methods, including optical sensors. In all fields, pollen beetles were found to be aggregated and beetle density was related to plant growth stage, with more beetles occurring on plants after the budding stage than before inflorescence development. Optical sensors were the most efficient monitoring method, recording pollen beetles 2 and 4 days ahead of water traps and counts from plant scouting, respectively. Optical sensors are a promising tool for early warning of insect pest immigration. The aggregation pattern of pollen beetles post immigration could be used to precisely target control in oilseed rape crops. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Understanding crop colonization of oilseed rape crops by the cabbage stem flea beetle (Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae)).

Development of accurate pest monitoring systems is essential for the establishment of integrated pest management strategies. Information about the pest behavior during the colonization process, as well as the sex and reproductive status of the colonizing population often are lacking and hinder their development. The cabbage stem flea beetle (CSFB, Psylliodes chrysocephala) can cause the complete destruction of oilseed rape crops (OSR, Brassica napus). In the present study, the colonization process of OSR fields by the CSFB was studied. More individuals were caught on the outward facing side of the traps than the side of the trap facing towards the crop at the field border and catches were higher on the trapping units at the center of the field than at its border, suggesting that more beetles were entering than leaving the crop. Catches were higher on lower traps placed near to the crop than on those positioned further from the ground and also were higher during the day than late afternoon and night. The sex-ratio of individuals caught was skewed towards males and sexual maturity was acquired for females during the experiment. Integration of sampling data with local meteorological data showed that the catches correlated mostly with air temperature and relative humidity. This study provides new information about the dispersion of the CSFB in OSR fields during the colonization process, and highlights correlations between local meteorological factors and activity of the CSFB, and represent a new step towards implementing monitoring strategies against this pest. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Indirect Evidence Based on Mating-Type Ratios for the Role of Sexual Reproduction in European and Chinese Populations of Plenodomus biglobosus (Blackleg of Oilseed Rape)

Blackleg (Phoma) disease, caused by the ascomycete fungi Plenodomus biglobosus and P. lingam, threatens oilseed rape (OSR; Brassica napus) crops internationally. In many parts of the world, both species co-occur, but in China only P. biglobosus has so far been reported. Plenodomus biglobosus reproduces asexually (pycnidiospores), but also sexually (pseudothecia-yielding ascospores), via a heterothallic mating system requiring MAT1-1 and MAT1-2 genotypes. However, the roles of airborne ascospore inoculum in driving blackleg disease outbreaks in China are less well understood compared to elsewhere in the world. This is despite the very different agronomic cropping practices in parts of China, in which paddy rice and OSR are often grown in rotation; OSR stubble is often submerged under water for long periods potentially affecting pseudothecial development. Here, we indirectly investigate the potential role of sexual reproduction by developing new polymerase chain reaction (PCR) -based mating-type diagnostics for P. biglobosus and subsequently screening an international collection of 59 European and 157 Chinese isolates. Overall, in both Europe and China, P. biglobosus mating types did not deviate from a 1:1 ratio, such as is generally thought to occur under frequency-dependent selection in sexually reproducing pathogen populations. Both mating types were balanced in all the individual European countries tested (Austria, France, Poland, UK). Conversely, in China, mating types were only balanced in the eastern region; in the northern and southwestern regions there were skewed ratios, more typical of predominantly asexual reproduction, towards MAT1-1 and MAT1-2, respectively. The implications of these findings and future research directions for improved understanding of P. biglobosus epidemiology on OSR, particularly in China, are considered.

Within-field floral resources have the potential to increase parasitism rates in winter oilseed rape pests more than resources at field margins

Pollen beetles (Brassicogethes spp.) and stem flea beetles (Psylliodes chrysocephala) are among the main pests of oilseed rape crops in Europe, causing high yield losses. Increasing insecticide resistance and environmental concerns have highlighted the need for alternatives to chemical control, such as conservation biological control. Conservation biological control can be enhanced by providing resources to beneficial organisms in and around crop fields. Flower strips are a promising tool to provide nectar resources for parasitoids. In addition, the planting of such resources in field margins should be reinforced by the absence of insecticide application. However, the presence and amount of weeds within the field could mitigate the effect of flower strips and needs to be explored. We surveyed 25 oilseed rape fields in 2019 and 2020. Ten of these fields were adjacent to a sown wildflower strip. We compared an eco-friendly strategy (wildflower strip without insecticide in spring) to a conventional approach (no wildflower strip and chemical control of pests). We assessed the parasitism of stem flea beetle and pollen beetle larvae in the spring, at distances of 5 m and 30 m from the wildflower strip or the natural field margin. We performed botanical surveys in wildflower strips and natural field margins and within the field, to assess the availability of accessible nectar resources to parasitoids. Stem flea beetle parasitism rates were not affected by the strategy used, but the eco-friendly strategy had a weak positive effect on pollen beetle parasitism. Unexpectedly, the amount of accessible nectar did not differ significantly between wildflower strips in the eco-friendly strategy and natural herbaceous field margins in the conventional strategy. The amount of accessible nectar provided by weeds in the field was positively related only to pollen beetle parasitism rates. By contrast, the amount of accessible nectar for both spontaneous field margin and flower strips had no effect on the rates of parasitism of either species. Parasitism rate decreased significantly with decreasing distance to the field edge, for both species. Our results suggest that further studies are required: (i) to improve the composition of wildflower strips, so as to provide more accessible nectar resources at the start of spring and (ii) to explore more management strategy options, notably on in-field resources management such as unsown patches or intercropping.

Earlier flowering of winter oilseed rape compensates for higher pest pressure in warmer climates

Abstract Global warming can increase insect pest pressure by enhancing reproductive rates. Whether this translates into yield losses depends on phenological synchronisation of pests with their host plants and natural enemies. Simultaneously, landscape composition may mitigate climate effects by shaping the resource availability for pests and their antagonists. Here, we study the combined effects of temperature and landscape composition on pest abundances, larval parasitism, crop damage and yield, while also considering crop phenology, to identify strategies for sustainable management of oilseed rape (OSR) pests under warming climates. In all, 29 winter OSR crop fields were investigated in different climates (defined by multi‐annual mean temperature, MAT) and landscape contexts in Bavaria, Germany. We measured abundances of adult pollen beetles and stem weevil larvae, pollen beetle larval parasitism, bud loss, stem damage and seed yield, and calculated the flowering date from growth stage observations. Landscape parameters (proportion of non‐crop and OSR area, change in OSR area relative to the previous year) were calculated at six spatial scales (0.6–5 km). Pollen beetle abundance increased with MAT but to different degrees depending on the landscape context, that is, increased less strongly when OSR proportions were high (1‐km scale), interannually constant (5‐km scale) or both. In contrast, stem weevil abundance and stem damage did not respond to landscape composition nor MAT. Pollen beetle larval parasitism was overall low, but occasionally exceeded 30% under both low and high MAT and with reduced OSR area (0.6‐km scale). Despite high pollen beetle abundance in warm climates, yields were high when OSR flowered early. Thereby, higher temperatures favoured early flowering. Only among late‐flowering OSR crop fields yield was higher in cooler than warmer climates. Bud loss responded analogously. Landscape composition did not substantially affect bud loss and yield. Synthesis and applications: Earlier flowering of winter OSR compensates for higher pollen beetle abundance in warmer climates, while interannual continuity of OSR area prevents high pollen beetle abundance in the first place. Thus, regional coordination of crop rotation and crop management promoting early flowering may contribute to sustainable pest management in OSR under current and future climatic conditions.