Entwicklung, Samenbildung und Biomasseproduktion ausgewählter Problemunkrautarten in Rapshalbzwerghybriden

Recently semi-dwarf oilseed rape varieties appeared in practical cropping. So far, only few studies about their properties in combination with weeds are available. Recently however an increasing number of weeds that are difficult to control are observed in oilseed rape. For the experiment Anchusa arvensis (L.) M.??Bieb., Sisymbrium officinale (L.) Scop. and a mixture of three different Geranium species were selected to study their development, seed and biomass production. Consequences for cropping on semi-dwarf oilseed rape cultivars were derived from the results. Three rape cultivars different in plant height were chosen for the experiments: the normal growing variety “Viking”, the semi-dwarf variety “PR45D01” and a full dwarf rape biotype for breeding purposes. In contrast oilseed rape with normal height, infestation of light-indigently and high growing weeds is more probable in semi-dwarf oilseed rape varieties. These weeds show increased biomass production and higher seed production per plant.     

Effects of fungicides on in vitro spore germination and mycelial growth of the phytopathogens Leptosphaeria maculans and L. biglobosa (phoma stem canker of oilseed rape)

BACKGROUND: Phoma stem canker, caused by the coexisting related fungal pathogens Leptosphaeria maculans (Des.) Ces. & de Not and L. biglobosa Shoemaker & H Brun, is a major disease of winter oilseed rape in the UK. Annually, over 90% of UK crops receive at least one foliar application of fungicide, but little is known about the sensitivity of the more damaging L. maculans and the less damaging L. biglobosa to these fungicides. The effects of flusilazole, tebuconazole and Methyl Benzimidazole Carbamate (MBC) fungicides (benomyl and carbendazim) on the germination of ascospores, conidia and germ tube growth of both species were examined. Isolates collected from different oilseed rape crops in England and Wales were assessed for their mycelial growth on fungicide‐amended medium, and ED₅₀ values were calculated. RESULTS: Leptosphaeria maculans and L. biglobosa differed in their sensitivity to fungicides. Conidial germination of L. maculans was more sensitive to these fungicides than that of L. biglobosa. Isolates of L. maculans had smaller ED₅₀ values for mycelial growth for all fungicides tested than isolates of L. biglobosa. CONCLUSION: These results suggest that fungicide applications might affect the structure of L. maculans/L. biglobosa populations in UK winter oilseed rape crops. Copyright © 2009 Society of Chemical Industry     

Response of imidazolinone-tolerant and -susceptible volunteer oilseed rape (Brassica napus L.) to ALS inhibitors and alternative herbicides

BACKGROUND: Imidazolinone-tolerant oilseed rape (Brassica napus L.) varieties are currently grown in Canada, North America, Chile and Australia with high acreage. A Europe-wide introduction has started and will be pushed further for both spring and winter varieties. The primary aim of this study was to evaluate the impact of imidazolinone tolerance for future volunteer oilseed rape control in subsequent crops, particularly winter wheat. RESULTS: A greenhouse bioassay showed cross-tolerance of imidazolinone-tolerant oilseed rape towards sulfonylureas, triazolopyrimidines and sulfonylaminocarbonyltriazolinones (resistance factors between 5 and 775), with a homozygous variety expressing a much higher tolerance level compared with a heterozygous variety. Calculated ED₉₀ values suitable for controlling tolerant plants were always much higher than the recommended herbicide dose. Generally, results were confirmed under field conditions, but with higher efficacies than expected in some cases (e.g. florasulam). Herbicides with an alternative mode of action were found to be effective in controlling imidazolinone-tolerant volunteers in subsequent winter wheat crops. CONCLUSION: Herbicide strategies have to be adjusted for volunteer control in subsequent crops if imidazolinone-tolerant oilseed rape varieties are to be grown. However, agronomic tools (harvest date, harvest technique, tillage) should be used conscientiously in the first place to keep volunteer oilseed rape densities at the lowest possible level. Copyright © 2012 Society of Chemical Industry     

Strategies to prevent spread of Leptosphaeria maculans (phoma stem canker) onto oilseed rape crops in China; costs and benefits

Field experiments in Europe have shown that Chinese cultivars of winter oilseed rape ( Brassica napus ) are very susceptible to the pathogen Leptosphaeria maculans (cause of phoma stem canker). Climatic and agronomic conditions in China are suitable for L. maculans since the closely related but less damaging pathogen L. biglobosa occurs on the winter and spring oilseed rape crops there. Major gene resistance to L. maculans is not durable; when introduced into commercial oilseed rape cultivars it is rapidly rendered ineffective by changes in the pathogen population. The threat to Chinese oilseed rape production from L. maculans is illustrated by the way in which L. maculans has spread into other areas of the world where previously only L. biglobosa was present, such as Canada and Poland. Models were developed to describe the spread (in space and time) of L. maculans across Alberta province, Canada, based on survey data collected over a 15-year period. These models were used to estimate the potential spread of L. maculans across the Yangtze river oilseed rape growing areas of China and its associated costs. Short-term strategies to prevent occurrence of severe phoma stem canker epidemics in China include training of extension workers to recognise symptoms of the disease and use of PCR-based diagnostics to detect the pathogen on imported seed. Long-term strategies include the introduction of durable resistance to L. maculans into Chinese oilseed rape cultivars as a component of an integrated disease management programme. The costs of such strategies in relation to costs of a phoma stem canker epidemic are discussed.     

Simulation of herbicide use in a crop rotation with transgenic herbicide-tolerant oilseed rape

The potential impact of herbicide-tolerant winter oilseed rape ( Brassica napus L.) on future herbicide use was investigated with a simulation model. The model uses a sigmoid function to simulate the growth of crops and weeds that compete for a maximum yield potential. Thresholds for weed control are based upon critical levels of weed biomass. The dynamics of the weed population are determined by the efficacy of representative herbicides on individual weed species and by seedbank parameters. Herbicide efficacy is determined by a log-logistic dose–response curve for each species. Simulation of a rotation with winter oilseed rape/wheat/wheat/barley showed contradictory predictions of herbicide use, because herbicide use in a rotation with either glyphosate- or glufosinate-tolerant oilseed rape was not reduced in the amount of kg a.i. ha^–1 compared with a traditional treatment, whereas the treatment frequency (number of standard recommended doses per unit area) decreased.     

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.     

Selective regulation of germination and growth of annual weeds by crop residues

Residues from mature, harvested crops of sorghum (Sorghum bicolor Moench.), sunflower (Helianthus annuus L.), oilseed rape (Brassica napus L.), wheat (Triticum aestivum L.) and field pea (Pisum sativum L.), exhibited selective effects on weed germination and growth under field conditions. Weed species in the study included Avena fatua L., Avena sterilis ssp. ludoviciana (Durieu) Nyman, Echinochloa crus-galli (L.) Beauv., Phalaris aquatica L., Phalaris paradoxa L., Lolium perenne L., Vulpia myuros (L.) Gmel., Hibiscus trionum L., Polygonum aviculare L., Bilderdykia convolvulus (L.) Dumort. and Lamium amplexicaule L. All crop residues tested, and in particular wheat and pea residues, promoted the germination and growth of A. fatua and A sterilis ssp. ludoviciana. Other grass weeds, however, were inhibited by the presence of crop residue, the extent of inhibition being dependent on residue type. Germination response of dicotyledonous weed species was also a function of residue type, H. trionum numbers were significantly higher in plots where oilseed rape, sorghum or sunflower residue had been incorporated, while L. amplexicaule was inhibited by these residue types and stimulated by pea and wheat residues.     

Horizontal movement of seeds following tine and plough cultivation: implicationsfor spatial dynamics of weed infestations

Horizontal movement of seeds by different cultivators was investigated in three experiments. Seeds of barley ( Hordeum vulgare L.), field bean ( Vicia faba L.) and oilseed rape ( Brassica napus L.) were positioned on the soil surface or buried 0.1 m deep prior to cultivation, Seed movement was assessed by counting germinated seedlings. The type of tine implement used significantly affected mean seed movement, with surface-sown seeds being moved significantly further than buried seeds. Primary cultivation with flexi- or spring-tine machines moved seeds further than straight-tine or power harrow implements. However, there was no overall difference between plough and flexi-tine mean seed movement. A single pass with a tine attached to a seed drili moved seeds less than the two passes with tine plus seed drill, but the first pass had the greatest effect. Small oilseed rape seeds moved significantly further than larger barley or field bean seeds. More than 84% of seeds moved ≤ 1m from the source: no seeds were observed>4.8m in a forward direction or >0.2m backwards from the source, In a fourth experiment, plots containing seeds of Sinapis arvensis L. were cultivated in alternate directions in successive years, The results broadly validated the findings of the previous experiments Quantifying the horizontal movement of weed seeds is important to the understanding of the spatial dynamics of weed patches and thus in the prediction of future weed distributions.     

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.     

Interference between triazine-resistant Brassica napus and Panicum miliaceum

Atrazine carryover often limits growers to production of atrazine-tolerant crops the year following application, and allows the increase of triazine-tolerant weed species such as Panicum miliaceum L. (wild proso millet). Tiriazine-resistant Brassica napus L. cv. ‘Triton’ (oilseed rape) was tested to characterize the nature of interspecific interference with P. miliaceum. In a greenhouse study, atrazine at 2.2 kg ha^?1 depressed oilseed rape fruit (siliqua) number and fruit dry weight, and delayed flowering, but did not significantly affect height or weight of shoots, Oilseed rape fruit weight was reduced at 200 P. miliaceum plants m^?2. fruit number and shoot weight were inhibited at 400 weeds m^?2. and height was reduced and flowering delayed at 600 weeds m^?2. Number and weight of fruits were reduced by one-third after 8 weeks of interference as compared to oilseed rape grown with the weed for 4 weeks. Oilseed rape height was reduced by 29% and shoot weight by 55% by 600 weeds m^?2 and 2–2 kg ha^?1 atrazine, while fruit number and weight were reduced by 72%. Oilseed rape shoot weight was reduced by 74% by 600 weeds m^?2 for 12 weeks of interference, while fruit number and weight were reduced by 85% and 82%. respectively. In a field study, fluazifop reduced early season P. miliaceum cover by 72%, but did not increase oilseed rape cover. Mid-season P. miliaceum shoot weight was decreased by 97% by fluazifop and oilseed rape shoot weight was increased by 34%. P. miliaceum control increased oilseed rape biomass by 38% at 89 days, but biomass of oilseed rape sown at 11.2 kg ha^?1 with 2.2 kg atrazine ha^?1 was not decreased by P. miliaceum interference at 89 days.     

硅和白粉病对长豇豆叶片叶绿素荧光参数和抗病相关酶活性的影响

白粉病Sphacerotheca fuliginea（Schlecht．）Poll．是长豇豆Vigna unguiculata ssp．sesquipedlis（L.）Verd．重要的叶部病害，寻找防治白粉病安全有效的方法已成为生产中的重要课题之一。硅对植物抗真菌病害的作用已引起国内外学者的广泛兴趣，可溶性硅的应用为植物抗病性研究提供了一条新的思路和方法。作者研究了硅和接种白粉病菌处理对长豇豆叶片叶绿素荧光参数和抗病相关酶活性的影响，旨在阐明硅提高长豇豆对白粉病抗性的作用机理。     

Survival of Leptosphaeria maculans in soil on residues of Brassica napus in South Australia

The survival of Leptosphaeria maculans , which causes phoma stem canker (blackleg), on oilseed rape residues ( Brassica napus ) in South Australia was investigated. Using a quantitative polymerase chain reaction (PCR) assay for L. maculans DNA, the pathogen was mainly detected in the upper 5 cm of the soil profile, including residues on the soil surface. As the size of organic matter particles in the soil decreased, so did the quantity of L. maculans detected in them. To obtain representative data for a field, at least 30 subsamples needed to be collected over the 0·81 ha area studied. In a survey of 49 commercial fields in South Australia, most L. maculans was detected in fields 1 year after oilseed rape had been grown, with less detected after 2 years and negligible amounts 3 years or more after cropping. The diagnostic DNA-based assay for L. maculans reduced the time and cost of studying L. maculans survival in soil and increased the sensitivity and accuracy of results compared with estimates of propagule number of colony-forming units on a semiselective medium.     

High resistance to pyrethroid insecticides in the Polish pollen beetle (<Emphasis Type="Italic">Meligethes aeneus F.</Emphasis>): the role of oxidative metabolism

Pollen beetle (Meligethes aeneus F.) (PB) causes very serious problems in oilseed rape (Brassica napus var. oleifera L.) cultivations in Poland and other European countries. Pyrethroid insecticides are the most frequently used type for controlling PB in Poland. This chemical group has been used in Poland since the beginning of the 1980’s and its strong selection pressure on PB resulted in some level of resistance of this pest to many active substances. The aim of this investigation was to analyze, with the use of synergists, the main mechanisms responsible for resistance of PB to pyrethroids. The results indicate the main resistance factor in Polish PB populations to be monooxygenase enzymes.     

Erodium cicutarium density and duration of interference effects on yield of wheat,oilseed rape,pea and dry bean

Field studies were conducted to determine the effect of various densities and duration of interference of Erodium cicutarium (L.) L'Her. ex Ait. on the yield of wheat, oilseed rape, pea and dry bean. The magnitude of yield reductions caused by E. cicutarium differed among the crops. Results indicate that the ranking of crop tolerance to E. cicutarium, when established at their recommended planting densities, was wheat > oilseed rape > pea ? dry bean. Maximum yield reduction occurred at E. cicutarium densities of 100–200 plants m^?2 and were 36% for wheat, 37% for oilseed rape, 82% for dry bean and 92% for pea. Crop yield progressively decreased as the duration of E. cicutarium interference increased. Three weeks of E. cicutarium interference after emergence was sufficient to reduce the yield of all crops, indicating the importance of controlling this weed early in the growing season. The mean yield reduction for each week of E. cicutarium interference was 1·6%, 2·7%, 3·6% and 6·3% for wheat, oilseed rape, pea and dry bean respectively. E. cicutarium is therefore a weed that warrants consideration for control in annual cropping systems.     

Modelling crop:weed interactions in wheat with ALMANAC

ALMANAC is a dynamic model for plant growth, water balance and soil nitrogen dynamics that can simulate on a daily basis two or more competing species. The simulation of competition for light is based on Beer's law, allowing a different extinction coefficient ( k ) for each species. Light is partitioned between species based on k -values, leaf area index and plant heights. Total hiomass is simulated with radiation use efficiency and grain yield with a harvest index approach, sensitive to water stress. The model simulates competition for water and nutrients based on each species current rooting zone and demand by each species. The effect of crop management on the competition issue can he simulated. The model was evaluated in Dijon (France) using 4 years of experimental data on wheat:oat mixtures, differing in oat ( Avena sativa L.) densities, the period of oat emergence, the date of weed suppression by herbicides and the wheat ( Triticun aestivum L.) genotype. Additional data on oilseed rape ( Brassica nupus L.) and vetch ( Vilcia sauiva L.) competition in spring wheat were also used. The wheat grain yield was reasonably simulated with a root mean square error (RMSE) of 0.10-0.35 t ha^-1. Corresponding values for oats were 0.10-0.55 t ha^-1. The competitiveness of oats, oilseed rape and vetch was correctly simulated. The model appears as a reasonable tool for estimating damage thresholds in integrated weed control programmes.     

Splash dispersal of Leptosphaeria maculans pycnidiospores and the spread of blackleg on oilseed rape

The fungus Leptosphaeria maculans causes blackleg (phoma stem canker), one of the most serious diseases of oilseed rape. The role of pycnidiospores produced during asexual reproduction is poorly documented and limits the understanding of the pathogen's population dynamics. The objectives of this study were to assess rain-splash dispersal of pycnidiospores of L. maculans from phoma leaf spots, and transmission of the disease from oilseed rape stubble carrying pycnidia. The work was conducted in still air with either a drop generator or a rain simulator. The impact of simulated incident drops on phoma leaf spots resulted in the dispersal of L. maculans pycnidiospores within splash droplets. Ninety per cent of the spores were collected within 14 cm of the source and a few were regularly observed up to 40 cm. Pycnidiospores produced on oilseed rape stubble and dispersed by simulated rain infected oilseed rape trap plants in a spatial pattern that matched the spatial dispersal of the pycnidiospores. In the field, rain-splash dispersal of pycnidiospores could increase the pathogen population and may enhance sexual reproduction by facilitating the mating of initially spatially separated isolates of opposite mating type.     

Pyrethroid resistance monitoring in European populations of pollen beetle (Meligethes spp.): a coordinated approach through the Insecticide Resistance Action Committee (IRAC)

BACKGROUND: Pollen beetle (Meligethes spp.) is a major pest of European oilseed rape crops. Its resistance to pyrethroid insecticides has been recorded in samples of beetles collected in Europe since at least 1999, and problems with the control of the beetle in the field have been widely reported. In 2007, a Pollen Beetle Working Group was formed through the Insecticide Resistance Action Committee (IRAC) in order to coordinate efforts for surveying pyrethroid resistance development. RESULTS: The results of the first 3 years of the pollen beetle pyrethroid susceptibility survey using a laboratory test are presented in this paper. Resistant beetle samples were collected from 20 of the 21 countries surveyed, with a general trend of increasing frequency and spread of resistant samples in European oilseed‐rape‐growing regions. CONCLUSION: Pyrethroid‐resistant beetles dominate in Western and Central Europe and are becoming established in the North and East, the main oilseed‐rape‐growing areas of Europe. The development and spread of pyrethroid‐resistant pollen beetles highlights the need for effective management strategies for oilseed rape insect pests. Copyright © 2011 Society of Chemical Industry     

Kohlfliegenauftreten im Raps

A new pest in oilseed rape the cabbage root fly (Delia radicum L.) has succeded to establish – at least regional –during the recent years. It is not easy to monitor the cabbage root fly. Although the usual yellow water trap works quite well, it is still difficult for the farmers to determine Delia radicum exactly. The amount of infestation can be assessed best in the middle of November by analysing the damages of the roots. In this article a classification scheme is proposed. It is also difficult to control this pest. While applications of Pyrethroids against the imagines and the use of Dimethoat against the larva mostly showed only little effect in the tests, some new dressing-substances proved better against the standard “Chinook” (Imidacloprid+beta-Cyfluthrin). To forward this research and to clarify factors, which influence the infestation, a project titled “Possibilities of defence and control of cabbage root fly in winter oilseed rape” has been started in November 2003. Eight crop-protection services at German Federal State level and the BBA are involved in this project, which is supported by UFOP.     

Survival of Leptosphaeria maculans and associated mycobiota on oilseed rape stubble buried in soil

Leptosphaeria maculans , the causal agent of phoma stem canker on oilseed rape, is an important pathogen in oilseed rape growing regions of the world, including Australia. Survival of L. maculans and associated mycobiota on oilseed rape stubble buried for 13 months in field soil and in sandy soil was studied under South Australian environmental conditions. Stubble weight decreased significantly by the end of the burial period, more so in field (53·7%) than in sandy soil (22%). Pseudothecia did not develop on stubble buried in field soil and few formed when buried in sandy soil. Moist incubation of stubble following retrieval from both media generated pseudothecia; however, pseudothecial development ceased on stubble that had been buried for 10 and 12 months in field and sandy soil, respectively. In total, 20 and 36 genera of fungi were isolated from stubble before and after burial, respectively. Alternaria spp., L. maculans and Stemphylium botryosum were isolated from 81·7, 70 and 60% of stubble pieces before burial, respectively. Isolation frequency of these species decreased significantly throughout the burial period in both media. Conversely, isolation frequency of Stachybotrys chartarum , Fusarium spp. and Trichoderma spp., having pre-burial frequencies of 26·7, 16·7 and 2·5%, respectively, increased over the burial period regardless of soil type. These findings suggest that inoculum production of L. maculans decreases with the increasing burial duration in field soil over 10 months, before ceasing, and this may be due to associated mycobiota.