Prediction of competition between oilseed rape and Stellaria media

Ten experiments have investigated competition between winter oilseed rape and Stellaria media (common chickweed). Yield losses caused by this weed were often high, but differed greatly between experiments, 5% yield loss being calculated to be caused by 1.4–328 plants m^?2. Predictions of yield loss based on relative weed dry weights [weed dry weights/(crop + weed dry weights)] in December were somewhat less variable than those based on weed density, 5% yield loss being caused by 1.4–10.6% relative weed dry weight. The variations in yield loss were related to variations in the competitiveness of the oilseed rape and the S. media, caused by weather differences between years and sites, and the long period between weed assessment and harvest (8–10 months). However, despite the lack of precise relationships, there were indications that the greater the crop dry weights in December, the lower the final yield loss. Delayed sowing of oilseed rape until late September did not clearly increase the competitive effects of the weed compared with late August/early September sowings. Weed competition was not clearly affected by reduced crop density (44–113 plants m^?2), because of the compensatory ability of the lowest density. The results of the experiments are discussed in relation to the prediction of yield loss and, thus, possible adjustment of weed control strategies to meet expected crop losses.     

Herbicide sensitivity of transgenic multiple herbicide-tolerant oilseed rape

Glyphosate and glufosinate-ammonium herbicide tolerance traits were combined into both winter and spring lines of Brassica napus L. This allowed the study of possible interactions between these transgenes in two genetic backgrounds when treated with a variety of herbicides. Selective herbicides that are commonly used within Brassica crops showed no adverse effects on the transgenic plants or their null controls. Lines containing both glyphosate and glufosinate transgenes remained tolerant to their respective herbicides, regardless of the presence of the second tolerance transgene. Lines containing only a single transgene retained tolerance to the encoded trait and did not show cross-tolerance to the second. Null lines were killed by either herbicide. All plant lines, regardless of their transgene content, were found to be equally susceptible to three herbicides (paraquat, metsulfuronmethyl and mecoprop), commonly used to remove volunteer B napus from succeeding crops and set-a-side land.     

Differential host-parasite interactions between oilseed rape and Leptosphaeria macufans, the causal fungus of stem canker

Seedlings of 13 cultivars of oilseed rape ( Brassica napus ) were inoculated with 10 isolates of Leptosphaeria maculans. Three virulent isolates were identified which gave a resistant reaction on some cultivars normally considered susceptible. Further experiments to compare these with standard isolates confirmed the existence of a differential host-pathogen interaction. The breeding line 78/271, plus the cultivars Quinta, Garant, Norli and possibly Elvira differentiated the isolates tested while Jet Neuf, Rafal, Primor, Doral, Hercules, Rapora, Liraglu and Erra did not. The relevance of these findings to breeding for canker resistance in oilseed rape is discussed.     

Latent infection of winter oilseed rape by Leptosphaeria maculans

Plants of oilseed rape, cultivars Primer and Jet Neuf, were grown in a glasshouse and inoculated at G.S. 2.4–2.7 with pycnidiospores or ascospores of Leptosphaeria maculans. The plants were kept for a further 2–4 weeks at 14°C and then transferred, together with uninoculated plants, to a polythene tunnel in winter. The majority of stems of inoculated plants did not have macroscopic symptoms of L. maculans infection 6 weeks after inoculation. Examination of whole mounts of peripheral tissue and transverse sections of fixed and embedded portions of these stems revealed intercellular septate fungal hyphae, often deep in non-necrotic cortical tissue, in symptomless inoculated plants but not in uninoculated plants. L. maculans was recovered following surface sterilization of adjacent portions of the same stems. When symptomless inoculated plants were transferred to a glasshouse at 18–20°C, cankers soon developed. The significance of these latent mycelial infections to canker development in the field is discussed.     

Biological control methods of pest insects in oilseed rape

Parasitoids, predators, insect pathogenic fungi, nematodes and microsporidia have all shown promise in the biological suppression of the key target pest, the pollen beetle Meligethes aeneus in rapeseed, as well as in the control of other rapeseed pests. Under favourable conditions pollen beetles are locally and temporarily already under efficient natural control by one or several of these agents, but overall the pollen beetle remains the number one pest of rapeseed in Finland, as well as elsewhere in Europe. Conservation biological control to enhance natural control appears the most feasible approach to solve the problem. Field and simulation data are used to demonstrate how a simple change in the tillage practice may be enough to obtain efficient control of the pollen beetle. Several other options are, or will be available, subject to successful registration of microbial products based on the fungi Metarhizium anisopliae and Beauveria bassiana , and the nematode Steinernema feltiae . Strategies and methods of applying these agents have been developed to facilitate either inundative treatments, or ecosystem restoration to (re-)establish the presence of these agents in agricultural fields. Critical components of agricultural practice have been identified for maximising control by biological agents within a functioning IPM system.     

Mating system in Hirschfeldia incana and hybridization to oilseed rape

Concerns have been raised about the possibility of sexual transfer of herbicide resistance genes from transgenic crops towards weedy relatives. The average rate of spontaneous hybridization between Hirschfeldia incana (L.) Lagrèze-Fossat and oilseed rape ( Brassica napus L.) was 0.6 hybrids per plant over 3 years of field experiments using herbicide-resistant oilseed rape as a pollen donor. Self-incompatibility was shown to be the mating system of most individuals within a population of H. incana , although some plants had some ability to self-fertilize, which could mitigate gene flow. Back-crossing interspecific hybrids to H. incana over five generations showed that introgression was not successful in our experiment.     

Weed flora shifts and specialisation in winter oilseed rape in France

Temporally repeated data sets can provide useful information about the management practices governing changes in the arable weed flora. This study aimed (i) to investigate changes in the most common weed species in winter oilseed rape crops in France between the 1970s and the 2000s and (ii) to pinpoint the main plant biological traits and associated management practices underlying the development of a specific weed flora in this crop. We compared two large‐scale surveys covering France in the 1970s and the 2000s, the later survey including several floristic samplings, on two dates, and both herbicide‐free control and treated plots. This last survey aimed to identify the species best able to maintain high densities over a growing season of oilseed rape. Since the 1970s, the frequency of two‐thirds (69%) of the 26 most common species has changed, spectacularly in some cases, with several species once considered rare becoming very common (e.g. Geranium dissectum) and, conversely, some formerly common species becoming rarer (e.g. Stellaria media). Our results indicated a general strong increase in specialist weeds of oilseed rape. Weed species success was favoured by tolerance to oilseed rape herbicides and germination synchronous with the crop. The proportion of specialist oilseed rape weed species tended to increase with herbicide treatment intensity and to decrease with increases in the proportion of spring‐sown crops in the rotation. Changes to the rotation may therefore constitute an additional or alternative means of controlling some weeds well adapted to oilseed rape crops.     

The production and release of ascospores of Pyrenopeziza brassicae on oilseed rape

The results of observation for three seasons in oilseed rape crops of the production and release of ascopores of Pyrenopeziza brassicae , the cause of light leaf spot disease of brassicas, are presented. Large apothecia (1–2 mm in diameter) take at least 3 weeks to develop on leaf petioles after infected leaves die, but small apothecia (50–200 um) may form on leaf lamellae after about 15 days. Apothecia were found on all 12 oilseed rape varieties examined. Spore trapping experiments in infected crops show that ascospore release is associated with rain, but most ascospores are released after rainfall when the crop debris bearing apothecia are wet. Ascospores can be released for up to 5 days after rain. Laboratory measurements show that apothecia can continue to release ascospores for up to 3 weeks even when they are subjected to wet and dry cycles. The consequences of the widespread occurrence of the sexual stage of P. brassicae are discussed and possible cycles of disease and spore production in oilseed crops are suggested.     

Different methods of monitoring susceptibility of oilseed rape beetles to insecticides

The resistance of oilseed rape pollen beetles to lambda-cyhalothrin has increased in Germany over the period 2002 to 2007. Oilseed rape pollen beetles are very good at dispersing, therefore field results should always be compared with those of laboratory experiments. The response of oilseed rape pollen beetles to active substances may not be the same as that to formulated products. Bioassays in which beetles are exposed to insecticides on either complete inflorescences or flower buds give different results. It is evident that samples of the genus Meligethes collected in the field can include several different species. Monitoring for insecticide resistance should be done using only the true oilseed rape pollen beetle.     

Incidence of pyrethroid‐resistant oilseed rape pests in Germany

BACKGROUND: Failures in pollen beetle control using pyrethroids since 2005 indicated pyrethroid resistance in Germany. Therefore, resistance monitoring using bioassays was established in Germany for oilseed rape pest insects. RESULTS: The spread and intensity of pyrethroid resistance of Meligethes aeneus increased from 2005 onwards, with no sensitive samples left in any region of Germany in 2011. Sensitivity also declined for the newly introduced actives bifenthrin, etofenprox (both class‐I pyrethroids) and tau‐fluvalinate; all three claimed to be less affected by resistance, although there was no clear cross‐resistance to lambda‐cyhalothrin (class‐II pyrethroid). In the German region with the longest tradition and high intensity of oilseed rape production, pyrethroid resistance of Psylliodes chrysocephala and Ceutorhynchus obstrictus, with resistance factors of up to 81 and 140 respectively, was detected. CONCLUSION: The intensive use of only one mode of action for many years is risky, because even pest insects with a low intrinsic resistance risk may develop resistance. Therefore, resistance strategies need to include several control options for pest insects needing regular treatments. Copyright © 2012 Society of Chemical Industry     

Possibilities for integrated control of winter oilseed rape diseases in Latvia

The sowing area of winter oilseed rape in Latvia has been rapidly increasing during the last 10 years, therefore oilseed rape diseases have become an important risk factor. The present paper reports 4‐year data (2008–2011) on different fungicide application systems (including forecasting systems) tested in field trials in Central Latvia. The development of stem canker (Leptosphaeria spp.) and white stem rot (Sclerotinia sclerotiorum) was evaluated depending on fungicide application schemes. Stem canker was found to be a widespread disease, and coexistence of both L. maculans and L. biglobosa was established in Latvia. There was no epidemic of white stem rot observed during the investigation period (incidence of disease was only 0.7–4.5%). Application of fungicides significantly (P < 0.05) decreased severity of stem canker. However, substantial differences between different treatments were not detected. Yield of oilseed rape fluctuated at about 4.5 tonnes ha^?1, and use of fungicides did not increase the yield. It was found that DaCom Plant Plus program had overestimated the risk of white stem rot in years with low disease pressure, whereas the Swedish model of forecasting, based on the risk‐point system, had produced acceptable forecasts.     

A survey of weeds of oilseed rape in central southern England

Weeds in a total of 450 fields of winter oilseed rape in nine areas of central southern England were surveyed, just prior to harvest during summer 1985, to identify those that had survived herbicide treatment or had not been sprayed and, thus, were capable of re-infestation or contamination of the harvested crop. Sixty-two species were identified; their levels of infestation were scored and distribution within the field noted. The most frequent species was Galium aparine, which occurred in 57% of fields. Mayweeds (Tripleurospermum inodorum, Matricaria recutita and Anthemis cotula) occurred in 23% of fields and Papaver rhoeas in 21%. All other species occurred in less than 20% of fields, the most prevalent being Sonchus asper(18%). Grassweeds were relatively infrequent, reflecting the widespread use of effective graminicides; the most prevalent was Arena spp., found in 9% of fields. Although most species were distributed throughout the field, Geranium dissection (13%) and Sisymbrium officinale (7%) were virtually confined to field margins (extending 1 m into the crop) and headlands (10m into the crop), respectively. Several species exhibited a well-defined regional distribution; Silene alba was virtually restricted to the most southern counties surveyed, whilst Papaver rhoeas and Viola arvensis were conspicuously absent from the eastern area.     

Predicting the risk of weed infestation in winter oilseed rape crops

Chemical weed control before crop and weed emergence is a systematic practice in winter oilseed rape crops in France. It would be profitable both for farmers and the environment to predict the level of weed infestation early on in the growing season and to control weeds only when necessary using post‐emergence weed control. The objective of this paper was to develop and evaluate simple models to predict weed biomass in oilseed rape crops. The model input variables were related to weed population characteristics and farmers’ practices. The models can be used to classify oilseed rape plots into two categories: plots with a level of weed infestation above a threshold or those with level of weed infestation below a threshold. A data set including 3 years of experiments, conducted across several regions in France, was used to estimate the parameters and to evaluate the models. High values of sensitivity and specificity were obtained when weed biomass was predicted as a function of sowing date, type of soil tillage, soil mineral nitrogen, crop density, weed density at emergence, and main characteristics of the most abundant weed species. Model performance strongly decreased when input variables related to the weed population were not taken into account. The best models correctly classified 90% of the plots with high weed infestation and 64% of the plots with low weed infestation.     

The metabolism of a novel herbicide ZJ0273 in oilseed rape and crickweed

Experiments were conducted to investigate the metabolism of a novel herbicide ZJ0273 in the seedlings of the susceptible crickweed and tolerant oilseed rape. Six metabolites of ZJ0273 were identified in crickweed seedlings, compared to 8 metabolites in oilseed rape. Among these metabolites, the metabolite M7, with the chemical name of 2-(4,6-dimethoxypyrimidin-2-yloxy) benzoic acid, was found to be the most herbicidally effective molecule with significant inhibition to acetolactate synthase. The differences in the amount and rate of ZJ0273 transformation to M7, and its metabolic detoxification, contributed to the primary mechanism of herbicidal selectivity of ZJ0273.     

Ecological approaches to the control of pollen beetles in oilseed rape

At a time of increasing demand for rapeseed oil for biofuel and food use and as increasing areas are grown, the risk of pollen beetle resistance to pyrethroids presents a significant threat to the sustainability of the oilseed rape crop and to farm incomes. Measures are urgently required to reduce the use of insecticides against pollen beetles, to preserve activity of the limited armoury of insecticides and minimise environmental pollution. In this paper, the status of pollen beetle resistance to pyrethroid insecticides and current control methods are presented from a UK perspective. Three ecological approaches to the control of pollen beetles that are based on research into their behaviour and ecology and that of their natural enemies are highlighted: use of monitoring, trap cropping and conservation biological control. These approaches have the potential to significantly reduce insecticide use against pollen beetles by helping to identify when spray thresholds have been breached, reducing pest incidence in the crop and increasing populations of natural enemies, respectively.     

Germination behaviour of dormant oilseed rape seeds in relation to temperature

Seeds of oilseed rape ( Brassica napus L., cv. Liglandor) were induced into secondary dormancy by imbibing them for 2-4 weeks in an osmotic solution at -1500 kPa in darkness. Treated seeds were then transferred into pots or Petri dishes, where they were given adequate water for germinatton. These pots and Petri dishes were exposed to various temperature regimes during the course of the following 6–14 months. During that time, seed samples were taken at 2- to 6- weekly intervals to monitor survival of seeds and to study their dormancy. The ntimber of seeds that had not germinated in pots or Petri dishes remained constant in the majority of treatments. but it declined when seeds were exposed to pronounced daily temperature alternations. This decline was due to germination and not to death of seeds from other causes. Germination tests on subsamples of seeds showed that they were light sensitive, more seeds germinating in the light than in the dark. The seeds'germination behaviour differed between samphng dates. This variation in germination behaviour appeared not to display the classical dormancy:non-dormancy cycle. Part of the variation seemed to be due to the changes in temperature that the seeds experienced when taken from pots and set up in the germination tests. Seeds exposed to a constant temperature for 1 year appeared lo become more dormant with time. The relevance of this work in relation to the persistence of volunteer oilseed rape is discussed.     

Occurrence and distribution of important weed species in German winter oilseed rape fields

Journal of Plant Diseases and Protection - Data on weed species currently found in winter oilseed rape, the extent of their occurrence and regional distinctions were collected in autumn 2005, 2006...     

Albugo Candida, the cause of a serious white rust of Lunaria biennis in Crete

Albugo Candida, the causal agent of white blister rust of Lunaria biennis and other crucifers. is recorded for the first time in Crete.