Oilseed Rape Fields Research Articles

Quantifying lodging-induced yield losses in oilseed rape

Lodging has been identified as one of the factors responsible for the lack of improvement in farm yields of oilseed rape. Despite this, no studies have attempted to quantify the cost of lodging at regional or national scales. The objectives of this study were to better understand the impact of timing and angle of lodging on seed yield and oil content of modern oilseed rape varieties, test whether a model predicting lodging-induced yield losses for wheat is appropriate for oilseed rape and quantify the extent of lodging in UK oilseed rape crops using an aerial photograph survey, estimating the consequential effects of lodging on the value of the crop at a national scale. Artificial lodging experiments showed that the crop developmental stage at which lodging occurred and the angle of lodging had a significant impact on yield, with lodging to 90° during flowering reducing yield by 46% and lodging to 45° during flowering reducing yield by approximately 20%. Variable, but usually smaller amounts of yield were lost when lodging occurred during seed filling. Reductions in oil content of the seed were greatest when lodging occurred to 90° at early flowering. Yield losses were mainly related to reductions in seeds/m2. A model for predicting lodging-induced yield losses in winter wheat was tested for its suitability in predicting the effect of different angles of lodging at different growth stages on yield in oilseed rape against the experimental datasets. This wheat model was based on existing models of canopy photosynthesis and respiration to account for lodging induced changes to the canopy and the impact on light capture and rates of photosynthesis and respiration. This was shown to provide a reasonable prediction of yield losses from lodging during flowering, which indicated that reductions in photosynthesis was the primary cause of yield loss. The model was less effective at predicting yield losses from lodging during seed filling and additional work is required to explore whether the model needs further development to be appropriate for sink limited crops such as oilseed rape. In 2012 and 2014, approximately 35% and 27% of oilseed rape fields surveyed in the UK contained some lodging respectively. It is estimated that lodging to 90° during early flowering could cost the UK oilseed rape industry£120 million per year and lodging to 45° during mid seed fill could cost £47 million per year.

Community-wide stable isotope analysis reveals two distinct trophic groups in a service-providing carabid community.

Disentangling trophic interactions among species is important for elucidating mechanisms underlying ecosystem functioning and services. Carabid beetles are an important guild of predators that may regulate pest populations in arable landscapes, but their generalist feeding behavior hinders predictions about their actual contribution to pest control. In order to assess carabids' potential for pest control, we simultaneously analyzed the carbon and nitrogen stable isotope ratios of a community of 45 co-occurring species in wheat and oilseed rape fields. With the expectation to identify distinct trophic groups based on the mean and the variance of carabid isotopic signatures, we observed a high degree of overlap in trophic positions between species. However, we also observed that species could be successfully categorized into two groups according to whether or not their carbon signatures varied independently from variations in the crop baseline. We interpret these results as differential primary resource uptake or by differential mobility aptitude in foraging. Accordingly, we propose that the isotopic signal can inform us on the presence/absence of links between generalist predators and cultivated plants through the trophic networks they belong to, and consequently on their potential role as pest natural enemies. We therefore suggest the complementarity of stable isotope analysis for obtaining a time-integrated assessment of carabid trophic behavior that may be combined with more direct molecular diet analysis allowing the simultaneous quantification of specific trophic links within agricultural landscapes.

Morphological and molecular identification of Leptosphaeria maculans in canola seeds and flowers collected from the North Iran

Blackleg disease, caused by Leptosphaeria maculans, is one of the most important diseases of rapeseed Brassica napus in Iran as in other regions of the world. The samples including canola petals and seeds were collected during 2014–2015 from canola field in North Iran. Isolates characteristics of fungus were assessed based on the colony growth rate and pycnidia in Potato Dextrose Agar. The pycnidia of the fungus were black, globose to subglobose in shape, the single-celled conidia, hyaline and fusiform with diameters of 4–5 × 1.5–2 μm. Most of the isolates were produced pigment in the liquid culture in variable color brown to black. Thirteen isolates were then separated into pathogenicity groups based on the interactions on B. napus differential cultivars. For the direct detection of seed contamination with L. maculans, PCR was developed using specific primers pair (LmacF, LmacR) which can amplify ITS1 and ITS2 along with the 5.8S rRNA region of L. maculans genome. Based on the followed information and sequence analysis, the fungal isolates from these samples were identified as L. maculans. The findings of this research showed that the disease was aggressive and highly distributed from infested seeds to oilseed rape fields.

Managing trap‐nesting bees as crop pollinators: Spatiotemporal effects of floral resources and antagonists

Abstract The decline of managed honeybees and the rapid expansion of mass‐flowering crops increase the risk of pollination limitation in crops and raise questions about novel management approaches for wild pollinators in agroecosystems. Adding artificial nesting sites, such as trap nests, can promote cavity‐nesting bees in agroecosystems, but effectiveness could be limited by the availability of floral resources in the surrounding landscape and by natural antagonists. In two European regions, we exposed artificial trap nests in paired field boundaries adjacent to oilseed rape (OSR) fields or non‐flowering crops for 2 years within 32 landscapes covering two independent gradients of OSR cover and semi‐natural habitat (SNH) cover in the landscape. We analysed the effects of local and landscape‐wide floral resource availability, land‐use intensity, landscape complexity and natural antagonists on community composition and population dynamics of trap‐nesting bees. Numbers of brood cells showed a strong, three‐fold increase in response to the additional nesting sites. Species richness and abundance of cavity‐nesting bees that were active during OSR flowering increased significantly with increasing amounts of early season landscape‐wide floral resource availability, such as the cultivation of OSR. Later foraging species benefited instead from the availability of late‐season alternative flower resources or SNH cover once the mass‐flowering had ceased. Density‐dependent parasitism increased following mass‐flowering, while no density‐dependent effect was found during mass‐flowering. Structural equation modelling revealed that the influence of floral resource availability on community growth rate was mediated by community size. Community size showed a strong negative effect on community growth rate. Despite positive density‐dependent parasitism, antagonists had only weak regulating effects on community growth rate. Synthesis and applications. Trap‐nesting bee populations grow markedly with the increasing availability of food resources in the landscape and effectiveness of trap nests is only marginally limited by natural antagonists. Thus, trap nests could be a simple pollinator‐supporting strategy to accompany the current expansion of mass‐flowering crops and to ensure pollination services for insect‐pollinated crops. Trap nests benefit, not only early season active generalist bees during oilseed rape flowering, but also species with later phenology if accompanied by other pollinator‐supporting practices.

Landscape effects on pollinator communities and pollination services in small-holder agroecosystems

Abstract Pollination by insects is key for the productivity of many fruit and non-graminous seed crops, but little is known about the response of pollinators to landscapes dominated by small-holder agriculture. Here we assess the relationships between landscape context, pollinator communities (density and diversity) and pollination of oilseed rape in 18 landscapes with proportions of small-holder farming ranging from 10% to 70% in southern China. To quantify the contribution of pollinators to oilseed rape yield, we manipulated pollinator access in a focal oilseed rape field in each landscape using open and closed cages. The pollinator communities in the focal fields were sampled using pan traps. The abundance of wild pollinators increased significantly with the proportion of cultivated land, but the diversity of the wild pollinator communities declined. The responses of pollinator abundance and diversity to cultivated land were best explained at scales of around 1000 m. The abundance of the unmanaged honey bee Apis cerana was positively associated with the proportion of cultivated land, whereas the abundance of the managed A. mellifera was not. A pollination services index (PSI) was calculated by comparing the reproductive investment in seeds between plants with or without pollinator access. PSI was positively correlated with wild pollinator abundance, but not with the abundance of honeybee species. PSI was also not significantly correlated with the area proportion of cultivated land. Our results indicate that crop dominated landscapes with numerous small fields supported an abundant, but relatively species poor bee community that delivered pollination services to oilseed rape. Conservation of (semi-)natural habitats, however, is important for maintaining the diversity of wild pollinators.

Nitrogen oxides and ozone fluxes from an oilseed-rape management cycle: the influence of cattle slurry application

Abstract. This study reports NO, NO2 and O3 mixing ratios and flux measurements using the eddy covariance method during a 7-month period over an oilseed-rape field, spanning an organic and a mineral fertilisation event. Cumulated NO emissions during the whole period were in agreement with previous studies and showed quite low emissions of 0.26 kg N ha−1 with an emission factor of 0.27 %, estimated as the ratio between total N emitted in the form of NO and total N input. The NO emissions were higher following organic fertilisation in August due to conditions favouring nitrification (soil water content around 20 % and high temperatures), while mineral fertilisation in February did not result in high emissions. The ozone deposition velocity increased significantly after organic fertilisation. The analysis of the chemical and turbulent transport times showed that reactions between NO, NO2 and O3 below the measurement height occurred constantly throughout the 7-month period. Following organic fertilisation, the NO ground fluxes were 30 % larger than the NO fluxes at the measurement height (3.2 m), while the NO2 fluxes switched from deposition to emission during certain periods, being negative at the surface and positive at the measurement height. This phenomenon of apparent NO2 emissions appears to be significant during strong NO emissions and high O3 ambient mixing ratios, even on a bare soil during August.

Migratory flight behaviour of the pollen beetle Meligethes aeneus.

BACKGROUNDThe field ecology of the pollen beetle Meligethes aeneus and its damaging effects on oilseed rape crops are well understood. However, the flight behaviour of M. aeneus, in particular the drivers for migratory movements across the landscape, is not well studied. We combined three established methodologies – suction traps, vertical‐looking radar and high‐altitude aerial netting – to demonstrate that M. aeneus flies at a range of altitudes at different points during its active season. RESULTSBy linking evidence of high‐altitude mass migration with immigration of pollen beetles into oilseed rape fields, we were able to ‘ground‐truth’ the results to characterise the seasonal movements of this pest across the landscape.CONCLUSIONWe demonstrate that this novel combination of methodologies can advance our understanding of the population movements of pollen beetles and could provide an opportunity to develop predictive models to estimate the severity and timing of pest outbreaks. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Agricultural land use shapes habitat selection, foraging and reproductive success of the Lesser Spotted Eagle Clanga pomarina

Anthropogenic loss of biodiversity is often indicated by the disappearance of top predators. However, some of them have adapted to man-made agricultural landscapes. Among raptors, one such example is the Lesser Spotted Eagle. We compiled an exhaustive data set on foraging habitat composition of this species by direct field mapping and detailed land cover maps to study the effect of various agricultural management practices on its occupancy of home ranges and productivity, as well as on its habitat utilization and hunting success. Home ranges of the Lesser Spotted Eagle contained more natural grasslands (7.6%) and other agricultural biotopes (29.9%) than expected by random, and they preferred to breed close to managed agricultural biotopes. They hunted preferably on grasslands, where they spent 86% of their time, especially on managed grasslands, but avoided arable fields. In total, 51% of the Lesser Spotted Eagle attacks were successful, and we detected no differences in hunting success among habitats. Nests of successfully breeding birds were surrounded by more crops/cultivated grassland on a rotational basis (19.0%), as well as by managed natural grassland (1.1%), than those of unsuccessful pairs (16 and 0.7%, respectively). We also detected a negative impact of oilseed rape fields and mowed cultivated grassland on the reproductive success of the Lesser Spotted Eagle, but these effects were not consistent over the years. Our results suggest that, although the Lesser Spotted Eagle is well adapted to foraging in traditional farmland, it is threatened by changes in agricultural practices and an increasing sown area of some crops, such as oilseed rape. Cultivation of various crops and retaining of grasslands, interspersed with set-aside and non-agricultural habitat patches, promoted by the European Union greening policy, would be favourable to the Lesser Spotted Eagle.

Wild pollinators enhance oilseed rape yield in small-holder farming systems in China

BackgroundInsect pollinators play an important role in crop pollination, but the relative contribution of wild pollinators and honey bees to pollination is currently under debate. There is virtually no information available on the strength of pollination services and the identity of pollination service providers from Asian smallholder farming systems, where fields are small, and variation among fields is high. We established 18 winter oilseed rape (Brassica napus L.) fields along a large geographical gradient in Jiangxi province in China. In each field, oilseed rape plants were grown in closed cages that excluded pollinators and open cages that allowed pollinator access. The pollinator community was sampled by pan traps for the entire oilseed rape blooming period.ResultsOilseed rape plants from which insect pollinators were excluded had on average 38% lower seed set, 17% lower fruit set and 12% lower yield per plant, but the seeds were 17% heavier, and the caged plants had 28% more flowers and 18% higher aboveground vegetative biomass than plants with pollinator access. Oilseed rape plants thus compensate for pollination deficit by producing heavier seeds and more flowers. Regression analysis indicated that local abundance and diversity of wild pollinators were positively associated with seed set and yield/straw ratio, while honey bee abundance was not related to yield parameters.ConclusionsWild pollinator abundance and diversity contribute to oilseed rape yield by enhancing plant resource allocation to seeds rather than to above-ground biomass. This study highlights the importance of the conservation of wild pollinators to support oilseed rape production in small-holder farming systems in China.

Effects of insecticides intended for Ceutorhynchus napi Gyll. control in oilseed rape on ground beetles

The effects of insecticides that are commonly used for conventional and integrated oilseed rape (OSR) management on ground beetles were studied. Monitoring of harmful species showed that only insecticides intended against Ceutorhynchus napi should be applied. There were no differences in beetle numbers and phenology of settling of C. napi in the OSR fields that received different management practices. The type of OSR management has a primary and significant impact on ground beetles abundance. Early in the spring, ground beetles settled more massively on the non-tilled OSR field with abundant weed cover and mulch on soil surface. However, there were no significant differences in species richness between the OSR fields managed differently. A total of 22 species were recorded. Early in the spring, the granivorous ground beetles Amara aenea (47.3%) and Harpalus distinguendus (32.5%) were dominant. When insecticides were applied, immigration of ground beetles began, so that their adverse effect was minimal. In both management systems the number of ground beetles and their diversity increased after spraying. In conclusion, no significant harmful effects of the insecticides on ground beetles were detected in OSR fields managed in two different ways.

Using the waggle dance to determine the spatial ecology of honey bees during commercial crop pollination

Managed honey bees play an important role in global crop pollination. Maximizing their potential is likely to be of increasing importance to the global human supply. We explored the potential of waggle dance data to determine the spatial ecology of honey bees sited in a crop under commercial pollination. Over two springs, we video recorded and then decoded 834 waggle dances from colonies located in two apple and pear farms in Kent, U.K. We also obtained pollen samples from returning foragers and quantified the insects visiting apple and pear flowers. The vast majority (84%) of dances were for locations outside of the orchards in which our colonies were located. Accounting for the distance of orchards and oilseed rape fields from the study colonies, the amount of foraging per hectare in oilseed rape fields was greater than in orchards. The results of the present study indicate that maximizing the pollination services of managed honey bee colonies requires an landscape level approach that takes into account farm and foraging scale, as well as competing floral sources. The data also suggest that oilseed rape is a significant competitor to apple and pear flowers for honey bee visits.

Mechanisms of Resistance to Pyroxsulam and ACCase Inhibitors in Japanese Foxtail (Alopecurus japonicus)

Japanese foxtail is a predominant tetraploid grass weed in wheat and oilseed rape fields in eastern China. In China, pyroxsulam is mainly used to manage annual grass weeds, especially those resistant to acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicides. Using dose–response studies, a pyroxsulam-resistant population, ACTC-1, was identified with a resistance index value of 58. Additionally, ACTC-1 was cross-resistant to sulfonylureas, imidazolinones, triazolopyrimidines, pyrimidinyl-benzoates, and sulfonylaminocarbonyl-triazolinones and multiresistant to ACCase and photosystem II inhibitors. Sequence analysis revealed four gene fragments encoding acetolactate synthase (ALS) from ACTC-1, and three from JNXW-1, a pyroxsulam-sensitive population. An Asp-376-Glu substitution was found in ALS1;2 and an Ile-2041-Asn in Acc1;1, which may be responsible for its resistance to pyroxsulam and ACCase inhibitors, respectively. In vitro assays of ALS activity revealed that in ACTC-1, the sensitivity of ALS to pyroxsulam was lower, and the basal ALS activity was twofold higher than that of sensitive population JNXW-1. Additionally, the combined application of pyroxsulam with malathion or piperonyl butoxide increased the sensitivity of ACTC-1 to pyroxsulam, although it could not completely overcome the resistance. It was inferred that both target-site-based resistance and nontarget-site-based resistance may be involved in the resistance to pyroxsulam.

Experimental evidence that honeybees depress wild insect densities in a flowering crop.

While addition of managed honeybees (Apis mellifera) improves pollination of many entomophilous crops, it is unknown if it simultaneously suppresses the densities of wild insects through competition. To investigate this, we added 624 honeybee hives to 23 fields of oilseed rape (Brassica napus L.) over 2 years and made sure that the areas around 21 other fields were free from honeybee hives. We demonstrate that honeybee addition depresses the densities of wild insects (bumblebees, solitary bees, hoverflies, marchflies, other flies, and other flying and flower-visiting insects) even in a massive flower resource such as oilseed rape. The effect was independent of the complexity of the surrounding landscape, but increased with the size of the crop field, which suggests that the effect was caused by spatial displacement of wild insects. Our results have potential implications both for the pollination of crops (if displacement of wild pollinators offsets benefits achieved by adding honeybees) and for conservation of wild insects (if displacement results in negative fitness consequences).

Rice Yield and the Fate of Fertilizer Nitrogen as Affected by Addition of Earthworm Casts Collected from Oilseed Rape Fields: A Pot Experiment.

The mechanism associated with improvement of soil nutritional status by oilseed rape crop, leading to better performance of rice crop, in rice-oilseed rape cropping systems is little known. The present study was aimed to test the hypothesis that earthworm casts produced during oilseed rape-growing season have positive effects on grain yield and fertilizer nitrogen (N) utilization in the subsequent flooded rice crop. A 15N-tracing pot experiment was conducted to determine the effects of earthworm casts collected from oilseed rape fields on yield attributes in rice and the fate of fertilizer N. Soil treated with earthworm casts (soil: earthworm casts = 4: 1, w/w) (EC1) produced 39% higher grain yield than soil only (EC0). EC1 had 18% more panicle number and 10% higher spikelet filling percentage than EC0. Aboveground biomass and harvest index were higher in EC1 than in EC0 by 20% and 15%, respectively. SPAD values in flag leaves were 10% and 22% higher under EC1 than EC0 at 15 and 20 days after heading, respectively. EC1 had 19% higher total N uptake and 18% higher physiological N-use efficiency than EC0. These positive effects of earthworm casts on yield attributes offset negative effects of decreasing N rate from 0.74 g pot–1 (equivalent to the recommended field rate of 150 kg ha–1) to 0.44 g pot–1 (equivalent to 60% of the recommended rate). Fertilizer N retention rate was 7% higher while fertilizer N loss rate was 6% lower in EC1 than in EC0. Our study suggests that earthworm casts produced during oilseed rape-growing season are expected to have the following benefits on the subsequent flooded rice system: (1) improving growth and physiological processes in rice plants and consequently increasing rice grain yield, and (2) increasing fertilizer N retention rate and hence decreasing fertilizer N loss rate and reducing environmental risk.

Using the stable isotope marker 13 C to study extrafloral nectar uptake by parasitoids under controlled conditions and in the field

Parasitic wasps are prominent natural enemies of crop pests. They usually feed on floral resources during the adult stage (nectar, pollen, or honeydew). Extrafloral nectar is an alternative source of sugar easily accessible to adult parasitoids. We developed an original method of nectar labelling based on the injection of labelled sugar solution into the plant stem in order to analyse the nectar uptake by parasitoids (cotton wick method). This method was used to artificially enrich extrafloral cornflower, Centaurea cyanus L. (Asteraceae), nectar with the stable isotope 13C. We analysed (1) the transfer of 13C from the sugar solution into extrafloral nectaries, (2) the uptake of labelled nectar by parasitoids under laboratory conditions, and (3) the ability of the method to discriminate, in an oilseed rape (Brassica napus L., Brassicaceae) field, between labelled parasitoids (i.e., those who have fed on labelled cornflowers located adjacent to the field) and unlabelled parasitoids to track parasitoid movements from the margin into the field. The extrafloral nectar of all test plants was 13C-labelled. Most (66%) of the parasitoids were identified as marked after 96 h of exposure to labelled plants in the laboratory. We could also detect labelled parasitoids inside the field, but the detection rate was only 1%. The experiments clearly demonstrate that the cotton wick method is appropriate to label extrafloral nectar and parasitoids feeding on this labelled nectar. Further research is needed on the amount of labelled extrafloral nectar required to obtain a sufficient marker level to track parasitoid movements in the field.

Large-scale monitoring of effects of clothianidin-dressed oilseed rape seeds on pollinating insects in Northern Germany: effects on red mason bees (Osmia bicornis).

The aim of this study was to investigate the effects of Elado® (10 g clothianidin & 2 g beta-cyfluthrin/kg seed)-dressed oilseed rape on the development and reproduction of mason bees (Osmia bicornis) as part of a large-scale monitoring field study in Northern Germany, where oilseed rape is usually cultivated at 25–33 % of the arable land. Both reference and test sites comprised 65 km2 in which no other crops attractive to pollinating insects were present. Six study locations were selected per site and three nesting shelters were placed at each location. Of these locations, three locations were directly adjacent to oilseed rape fields, while the other three locations were situated 100 m distant from the nearest oilseed rape field. At each location, 1500 cocoons of O. bicornis were placed into the central nesting shelter. During the exposure phase, nest building activities and foraging behaviour were assessed repeatedly. Cocoons were harvested in autumn to assess parasitization and reproduction including larval development. The following spring, the emergence of the next generation of adults from cocoons was monitored. High reproductive output and low parasitization rates indicated that Elado®-dressed oilseed rape did not cause any detrimental effects on the development or reproduction of mason bees.

Conventional and non-inversion tillage systems as a factor causing changes in ground beetle (Col. Carabidae) assemblages in oilseed rape (Brassica napus) fields

Background and purpose : Carabid beetles are among the most important elements of the natural environment’s resistance in arable fields. In this paper, the influence of different soil tillage systems on carabid beetle assemblages in oilseed rape plantations was studied. Materials and methods : The experiment was conducted in northeastern Poland. Six fields with oilseed rape cultivated under both conventional and non-inversion tillage systems were chosen. Barber traps were used to capture beetles. Results and conclusions: In total 9,968 individuals belonging to 56 species were collected. Significant differences in the abundance and species richness of ground beetles in two systems of soil tillage were observed. The abundance and species richness were significantly higher in the non-inversion tillage system. Analysis of the life history traits of carabids also revealed statistically significant differences in the seasonal occurrence of carabids related to the type of soil cultivation used.

Large-scale monitoring of effects of clothianidin-dressed oilseed rape seeds on pollinating insects in northern Germany: residues of clothianidin in pollen, nectar and honey.

This study was part of a large-scale monitoring project to assess the possible effects of Elado® (10 g clothianidin & 2 g β-cyfluthrin/kg seed)-dressed oilseed rape seeds on different pollinators in Northern Germany. Firstly, residues of clothianidin and its active metabolites thiazolylnitroguanidine and thiazolylmethylurea were measured in nectar and pollen from Elado®-dressed (test site, T) and undressed (reference site, R) oilseed rape collected by honey bees confined within tunnel tents. Clothianidin and its metabolites could not be detected or quantified in samples from R fields. Clothianidin concentrations in samples from T fields were 1.3 ± 0.9 μg/kg and 1.7 ± 0.9 μg/kg in nectar and pollen, respectively. Secondly, pollen and nectar for residue analyses were sampled from free flying honey bees, bumble bees and mason bees, placed at six study locations each in the R and T sites at the start of oilseed rape flowering. Honey samples were analysed from all honey bee colonies at the end of oilseed rape flowering. Neither clothianidin nor its metabolites were detectable or quantifiable in R site samples. Clothianidin concentrations in samples from the T site were below the limit of quantification (LOQ, 1.0 µg/kg) in most pollen and nectar samples collected by bees and 1.4 ± 0.5 µg/kg in honey taken from honey bee colonies. In summary, the study provides reliable semi-field and field data of clothianidin residues in nectar and pollen collected by different bee species in oilseed rape fields under common agricultural conditions.

Large-scale monitoring of effects of clothianidin-dressed oilseed rape seeds on pollinating insects in Northern Germany: effects on honey bees (Apis mellifera).

Possible effects of clothianidin seed-treated oilseed rape on honey bee colonies were investigated in a large-scale monitoring project in Northern Germany, where oilseed rape usually comprises 25–33 % of the arable land. For both reference and test sites, six study locations were selected and eight honey bee hives were placed at each location. At each site, three locations were directly adjacent to oilseed rape fields and three locations were situated 400 m away from the nearest oilseed rape field. Thus, 96 hives were exposed to fully flowering oilseed rape crops. Colony sizes and weights, the amount of honey harvested, and infection with parasites and diseases were monitored between April and September 2014. The percentage of oilseed rape pollen was determined in pollen and honey samples. After oilseed rape flowering, the hives were transferred to an extensive isolated area for post-exposure monitoring. Total numbers of adult bees and brood cells showed seasonal fluctuations, and there were no significant differences between the sites. The honey, which was extracted at the end of the exposure phase, contained 62.0–83.5 % oilseed rape pollen. Varroa destructor infestation was low during most of the course of the study but increased at the end of the study due to flumethrin resistance in the mite populations. In summary, honey bee colonies foraging in clothianidin seed-treated oilseed rape did not show any detrimental symptoms as compared to colonies foraging in clothianidin-free oilseed rape. Development of colony strength, brood success as well as honey yield and pathogen infection were not significantly affected by clothianidin seed-treatment during this study.

Clubroot – An Emerging Disease Faced by Czech Oilseed Rape Growers

AbstractClubroot is caused by the pathogen Plasmodiophora brassicae Woronin and has become a serious problem in oilseed rape production in the Czech Republic. The disease was previously widespread in commercial vegetable production and in hobby gardens. Whereas previously restricted only to the NE, since 2010 oilseed rape clubroot has been spreading across the whole country. A five-year monitoring of clubroot occurrence based on disease symptoms detection on oilseed rape fields was accomplished by the Union of Oilseed Growers and Processors. The presence of P. brassicae and clubroot symptoms was reported in all regions of the Czech Republic, except the Ústecký region, and in 31 out of 76 districts. At present, at least 130 fields are known to be infested by the pathogen, but this number is very likely underestimated. Some soil samples were also tested using the conventional polymerase chain reaction (PCR) method to evaluate the soil usability. All 14 suspected samples tested positive.